Chapter 8 Heating and Domestic Hot Water

Key Points to Learn

• New systems on the market now integrate domestic water heater with space heating. • How to avoid oversizing the heating appliance for your home while maintaining a sufficient safety margin. • Comparison and advantages of different fuel sources and heating systems. • Keeping heating systems simple and well-maintained are key factors in reliability and perfor- mance. • How to protect the health of your family with informed decision-making on heating. Heating Systems in temperature is below design temperature will have a minimal effect on the Alaska indoor temperature because the cool- Selecting a heating system for your down effect on a very efficient building home is a big responsibility, and can will be quite slow. This is another ben- take some time. The size of the system efit to building an energy efficient build- must be determined by doing a heat loss ing assembly. Proper sizing of the heat- calculation. Historically, heating systems ing system will improve comfort, save have been grossly oversized by using energy, and require less maintenance. rules of thumb and comparisons with oth- There are a number of Design Heat er buildings. This process has resulted in Loss Tools: a substantial waste of energy and unfor- • Manual J—This is the mechanical tunately it continues today. Small gains contractors handbook. have recently been made in this area of • ASHRAE Handbook of Funda- proper sizing from research that found mentals—The engineers approach for all heating systems in South-central Alaska building types and sizes. to be 121% oversized. (Alaska South- • AkWarm—This is Alaska’s own central Furnace Sizing Study, Cold-Cli- software, available for free. (www.absn. mate Housing Research Center, cchrc. com) org) In 1996 AHFC (Alaska Housing Fi- • Municipality Worksheets: Many nance Corporation) released AkWarm, building departments provide these for a software application for builders, free. designers, and home owners. AkWarm • Industry’s “Rule of Thumb” Usually can analyze energy use and calculate the results in grossly over-sizing efficient design heat load that is actually required homes. for the structure. • What’s in the truck. Or the “one size fits all,” contractor assured to be Heating System Design: over-sized. For the builder, the simplest method First Step: Determine the “Design is to have an energy rater perform an Heat Load” of the home. How much “energy rating from plans” on the pro- heat will you need on that really cold posed design. One of the reports Ak- day? What temperature is that really Warm generates is a design heat loss cal- cold day? It is not the coldest day ever culation. The AkWarm calculation has recorded, but a slightly warmer temper- been tested and monitored in numerous ature called the Outdoor Design Tem- homes and has been found to be very perature. These design temperatures accurate, generally, just slightly over- are published for most communities in sizing by 5%–10%, adding a reasonable Alaska. (Alaska Building Efficiency Stan- safety margin. dard (1998) Appendix D, 9 pages. also You may be hard pressed to convince included in the AkWarm computer pro- a mechanical contractor who has been gram.) Why not design for that worst living with the “Rule of Thumb” for 30 possible day? First of all, there is a lot years to downsize the system by 50% of safety built into the design heat loss no matter how efficient you built the calculation. Internal gains from lighting home. Two options: 1. Have the me- and appliances are ignored, yet make chanical contractor do a design heat loss up 10%–20% of the heat requirements calculation using their industry standard for an energy efficient home. Secondly, tool, Manual J, or; 2. Keep shopping for short-term periods where the outdoor

192 Chapter 8 a more knowledgeable mechanical con- fired appliances. Most locations in Alas- tractor. ka using above-ground tanks must use Second Step: Now that we know how number 1 (“arctic rated” ) fuel oil. This much energy we need to supply to heat ensures that the fuel will flow readily in the home. Next we need to decide on even the lowest temperatures. fuel types. Biodiesel is now available in Fair- Fuel Options: This choice is usu- banks, Anchorage and Juneau. Biodiesel ally an economic one based on the contains slightly less energy per gallon cost of fuel. Refer to the Building In than fuel oil, but works in some heaters Alaska Publication: Comparative Unit in place of number 2 fuel oil. Biodiesel Fuel Costs for Equivalent Dollar Net is typically around 30% cheaper than Heat Output. (Cooperative Extension diesel fuel. Check the manufacturer’s Publication, appended to this chapter: instructions for biodiesel/diesel mixes EEM-01152 ) or preheating before trying biodiesel in Electricity is generally most ex- your appliance. pensive per Btu, except for a few hydro- Natural Gas is still the most cost electric communities in Southeast effective fuel source where it is avail- Alaska. This may change as the cost of able in Alaska. Recent price increases in fuel oil has risen sharply at the time of natural gas have not been as extreme as this printing. New heat pump technol- with heating oil price increases. ogy for cold climates may soon prove to A few manufacturers offer heating be a cost effective alternative to oil or appliances that are easily converted be- propane. tween oil and natural gas, or propane. It Propane is more expensive per Btu may prove to be advantageous to install than heating oil, and in many cases, par- a system that can be easily modified to ticularly in rural Alaska, more expensive utilize one fuel or the other as necessary than electricity. but offers several advan- due to fuel availability and economics. tages. One example is a high efficiency Coal is rarely used in residential 90% + clean burning appliances that is heating systems today, but this may soon direct vent (sealed combustion). Today change. Many different strategies are there is much discussion what fuel oil available for burning coal. Some appli- prices will do in the future. If you are ances also accept wood as an alternative one who believes fuel oil will become fuel choice. Alaska has huge reserves cost prohibitive as a heating fuel, and of coal and wood/biomass and there is that natural gas or liquefied natural gas interest in preparing these fuels for lo- will become the fuel of choice, buying cal markets as other fossil fuels become into propane as a fuel for your heating higher priced. appliance is a choice to consider. Re- Wood is usually cheaper than oil, member, the more efficient you make and clean-burning wood appliances have your home, the less important small recently become easier to find on the differences in fuel costs will make. (Con- market, making the emissions more sider investing in the thermal efficiency in line with oil and gas based systems. of your home vs future oil purchases.) Wood is attractive because of its low Fuel-oil is the norm when natural cost, abundance, and environmental gas is unavailable. Other than small benefits. Wood technologies that are space heaters, direct vent boilers and compatible with hydronic distribution furnaces are not readily available. Tight- systems are available, but most so-called ly constructed boiler or furnace rooms outdoor wood-fired boilers should be are often necessary for most fuel oil avoided due to their low efficiency, high

Heating and Domestic Hot Water 193 emissions, and high cost. For example, work for you is simply good planning. masonry heaters provide a safe, even Many resources on capturing solar en- heat, and emit around 1-5 grams/hour of ergy are available. See again, “A Solar particulates (smoke). For a map of avail- Design Manual for Alaska” CES publica- able fuel types, energy density, and other tion EEM-01255. wood heating information, please go to In earlier years, when buildings were www.alaskawoodheating.com. constructed using little or no Building Plans are underway for wood pellet Science information, houses required plants in most Alaskan cities. Wood pel- very large inputs of energy to satisfy the let boilers can typically use various sizes winter heating requirement. Today, by of fuel hoppers, and are available in designing and assembling houses with many sizes. Pellet boilers usually incor- high levels of insulation, advanced win- porate some kind of auto-feed system so dows, exceptionally air-tight envelopes manual stoking is not required. Wood and controlled ventilation with heat pellets are made from low quality wood recovery, we are now able to minimize (typically), and are environmentally fuel inputs of all types. Such super en- friendly, clean, easy, and they are gener- ergy efficient types of houses are fuel ally cheaper than oil. flexible, exceptionally comfortable and Passive solar inputs should be de- inexpensive to operate. And remember, signed into new buildings to contribute improved health and minimal mainte- to heating the energy efficient home. nance are two rewards for following the Even though our northern latitude loca- Building Science approach to home con- tion causes much of our solar potential struction. to occur during summer months, pas- Third Step: Determine the Heating sive solar design attributes can soften System the financial blow from using only fossil The system should always be: fuels. Where any building site offers • Safe unobstructed southern exposure the • Efficient annual heating loads will be reduced by • Comfortable available passive solar inputs. Alaska will • Clean never be as solar friendly as Arizona or • Have reasonable service life Montana but ignoring the availability of • Easy to maintain. passive solar is not recommended (see One of the biggest decisions to be “A Solar Design Manual for Alaska,” for made when selecting your heating sys- further solar discussion. It is viewable tem is deciding between air-heating and by chapter at the Web site: www.alaska- hydronic, or water-based heating. We sun.org). will discuss the following types of space Solar thermal hot water also pro- heaters and combinations in more detail vides good benefit to reducing spring, below. summer and fall heating inputs. Decid- Space Heater ing early to incorporate passive solar • Forced-Air heating and solar thermal hot water are • Combinations intelligent design considerations we • Hydronic encourage you to make before pouring The following table is a quick guide concrete and driving nails! While this to the two main ways of distributing manual is an introduction to building heat in your home. The decision you science and energy efficient construc- make here will influence your entire tion, making all available alternatives building design. .

194 Chapter 8 Table H-1. So what type heating system is best for you? Hot Air Hot Water Pro Con Pro Con Lower Cost Expensive to zone Easy to zone Higher cost Low stand-by heat loss Noisy Quiet High mass boilers have high stand-by heat loss Can incorporate elec- Circulates dust & dirt Uses radiant heat water may need conditioning tronic air cleaner (mixing, valves, expensive) Can incorporate air con- Large space for ducts low cost hot water ditioning Expensive to distribute cheap to distribute Requires separate water Small size heater May be in out building

Space heaters: Small console heat- room doors should be left open as much ers such as the Toyo, Monitor, Rinnai, as possible. Many attempts of install- etc. offer direct venting with reason- ing a small thru-the-wall fan have ulti- able efficiencies. The elimination of a mately failed, with noise being a prime distribution system makes them much complaint. Also, the lack of any real less expensive to install and they use less improvement in raising temperatures electricity to move the heat around. In usually results in closing them off per- a small, very well insulated, open floor manently. The amount of heat actually plan home, a space heater can be an op- being delivered from a small flow of air tion with one big caveat; back rooms that is only a few degrees warmer than will generally be cooler. The more effi- the space it is trying to heat just doesn’t cient your building assembly, the warm- do much. Adding a little recirculation air er those back rooms will be, but with to those rooms could be a benefit. As an doors closed, they will be cooler. This is alternative, a space heater can provide simply unavoidable, and should be an- supplemental and backup heat to a cen- ticipated. Many folks like bedrooms to tral heating system, offering a little more be cooler, so a 5–10 degree cooler room piece of mind during our cold winters. may not be a big deal. For others, it Forced-Air Furnaces: These are would be. Caution is advised. very popular in South-Central Alaska, Our building science knowledge but fairly rare throughout the rest of reminds us that as we cool down the the state. A bias has developed against room air, the relative humidity goes up. forced-air systems. This is not because Higher relative humidity may result in they are a bad system, but because they condensation and mold growth. Mold are seldom designed and installed cor- growth is often found on exterior walls, rectly. Furnaces have advantages; com- especially in closets, at room partition bining ventilation air and supplying it to intersections, and where bedding or fur- the heating ducts reduces whole house niture makes contact with outside walls. ventilation costs. These systems also Whole house ventilation to the back provide opportunities to filter the air rooms can help maintain lower relative and condition it for proper humidity. humidity but will likely further lower Furnaces also have simpler controls, less room temperatures with the introduc- pumps, valves, and risk of water damage tion of cooler air into the room. Back from leaks.

Heating and Domestic Hot Water 195 Common problems with forced-air • Inadequate supply and/or furnaces: returns: Only a few years ago it was • Grossly over-sized. Over-sizing common practice to only supply air to requires larger ductwork and must dis- rooms and rely on a common return grill tribute much more air than necessary centrally located. These ducts are usu- causing drafts (discomfort) and more ally matched to a grossly over-sized fur- potential for noise. nace which moves a lot of air whenever • Leaky duct work: Tradition- it operates. What happens to a room if ally little attention was made to sealing we only push air into it, but don’t pull ductwork. Why bother if the ducts are air out of it? Mechanical contractors inside the house? Using a little of the should always balance the air flows in a building science learned in Chapter 2 forced-air system. lets look at the potential problems of leaky ducts. Note-The problem of inadequate • If there is a supply duct running supply and return ducting has been in a closed floor cavity with a few leaky partially resolved with contractors joints, what’s happening? The high pres- now putting return grills in most sure in the duct forces air out the leaks rooms. Unfortunately many contrac- into the cavity, pressurizing that cavity tors often do not attempt to balance slightly. At the far ends of that cavity the system. Simple pressure diag- there is likely to be a leaky rim joist. We nostics show rooms closest to the now have a pressure across the rim joist furnace pull more return air and are and a hole to outside. Pressure + hole thus depressurized. Rooms farthest = flow. We are now potentially increas- away still go slightly positive. If a bed- ing the flow of warm moist air thru the room is put directly above the garage building assembly increasing condensa- where the furnace is installed (that tion potential and rot of the rim joist. may be changing soon) that bedroom • If that cavity is used as a return is mechanically depressurized, sucking plenum to the furnace, we are now suck- more garage air and pollutants into ing on the rim joist and wall assembly the bedroom every time the furnace increasing air leakage and energy costs. comes on. Issues in the crawlspace: Many leaky return ducts will depressurize the • Installing ductwork in uncon- crawlspace. Not only does this increase ditioned spaces: Installing duct work air leakage into the crawlspace, but in attics s a cost cutting option that is also increases the potential of pulling seen on occasion. Leaky ducts whether soil gases like radon out of the ground supply or returns, are bad. The ducts and then delivers them directly into also replace what should have been insu- the house creating indoor air quality lation in the attic increasing heat loss to problems. Leaky return ductwork in the attic. This is clearly bad practice. a garage, or worse yet the entire leaky • Poor temperature control: furnace, will cause indoor air quality Many complaints come from small two problems. Oversights like those we’ve story condos where the downstairs is discussed may be responsible for cold and the upstairs too warm. Typi- childhood asthma, radon, which is the cally the thermostat is located upstairs. second leading avoidable cause of lung Thermostat calls for heat, the furnace cancer, and; carbon monoxide. Alaska fires and delivers a blast of warm air to has an especially high carbon monoxide all registers. What does building science mortality rate. say about warm air rising? The furnace

196 Chapter 8 doesn’t run long enough to actually priate flow requirements will determine warm up the lower level before the ther- proper supply and return duct sizing. mostat upstairs is satisfied. The open Energy efficient Brushless Per- stairway allows warm air from the lower manent Magnet (BPM) blower mo- floor registers to rise to the second tors are becoming more popular. (Same floor, adding more heat to the upstairs. as ECM motor which is a trademark The downstairs heat load is compound- of GE.) They are much more efficient ed by the air leakage entering the house than a conventional blower motor primarily on lower level, further adding and can save considerable electricity. to the comfort problem. Better furnace Studies report 40% electrical savings. sizing and duct layout would go a long (PIGG 2003, LBNL59865-2006). These way in resolving this comfort issue. smart blowers have the ability to vary A better forced-air system: the power to the motor to maintain a • Furnace sized appropriately to the constant air flow. For example, as fil- design heat load of the building. Bigger ters get dirty, air flows would normally isn’t better. be reduced, but with the BPM motor • Good duct sizing and layout. the controls would simply increase the Slightly oversized ducts are much bet- power supplied to the BPM motor and ter than undersized. Less noise and less maintain the same flow thru the fur- power (electricity) needed to move the nace, though electrical consumption will air, and provides a little safety margin to go up. The use of the new constant flow assure adequate flows to those farthest of BPM motors has one downside: poor rooms. maintenance. These expensive BPM • Balanced, little or no pressure dif- motors were not designed to operate ferences between rooms or floors. continuously under full load conditions • Very well-sealed ducts. If in doubt and premature failures have been com- have an energy rater do a duct leakage mon, and very expensive to replace. test during installation. This may be With increasing energy prices, the fu- your last chance to fix a problem. ture for BPM motors is promising, but • No ducts in garages or uncondi- current knowledge of their limitations tioned space by inexperienced heating system install- • Test the system to confirm proper ers should be considered in the selec- flows to rooms and temperature rise tion of furnaces. across furnace heat exchanger, check Mid efficiency and high efficien- that the safety high limit working prop- cy two-stage furnaces have become erly, and other checks recommended by popular options for furnace selection. manufacturer. They are available with standard PSC • Install a new medium to high effi- (Permanent Split Capacitor) motors and ciency furnace filter installed at start-up the efficient BPM. The furnaces operate which is in a location designed for ease on a low fire during much of the heat- of access. ing season, but when additional heat is • Homeowner guide for mainte- required, they go to a high firing rate. nance The furnace fan also operates at the low There are a number of guides for and high speed accordingly. Low speed proper duct sizing. Manual D is an in- operation is generally much quieter and dustry standard. Just as one should do less drafty. Longer run cycles offer bet- a design heat loss calculation for sizing ter temperature control for improved the heating system, a quick design heat comfort. Little or no fuel efficiency gain loss for each room to determine appro- has been reported with the two-stage

Heating and Domestic Hot Water 197 firing versus the conventional single heat, it signals the zone valves to open stage furnace. The standard PSC fur- and the circulating pump to start oper- nace blower motor is much less efficient ating. When a typical boiler’s internal on low speed than the BPM blower, so controller senses cold water it causes total energy savings is less with the stan- the burner to fire. Some cast iron boiler dard PSC motors over the BPM blower. systems have built-in safety features to As mentioned above, the BPM motor keep water that is too cold from mak- failure rate has been problem due to ing its way into the boiler, which could poor maintenance, duct design and/or crack it. Pressure relief valves set at no installation. The costly replacement of more than 30 PSI are absolutely neces- the BPM motors (reported to be as high sary to prevent pressure from building as $500) should be considered in the se- up in the boiler, and air venting valves lection of a furnace. should be installed at the highest point An important fact to be aware of in the system to relieve extra gases that is this: with an energy efficient home may build up. you simply do not need as much heat. It is now possible to purchase con- Smaller furnaces with less duct work densing oil and gas boilers with even save money. Spend some of it on better higher efficiencies than was traditionally design and installation, and use the sav- possible. Condensing boilers are able to ings for other energy improvements. extract more heat out of the combustion gases by allowing the combustion Hydronic Baseboard and gases to become liquid inside of the Radiant Floor Heat: boiler. In fuel oil boilers, this usually requires stainless steel tanks which Although the forced-air furnace can resist the corrosion of the sulfuric dominates the south-central Alaska acid in oil-based combustion liquids. market, hydronic heating is the stan- Experimental uses of condensing oil dard for most other regions in Alaska. boilers by the Cold-Climate Housing Hydronic heating, whether utilizing Research Center in Fairbanks have baseboards or a radiant floor system, shown that the acidic effluent can be offers multiple zoning, reduces noise, safely processed on-site through the use and is a comfortable heat option. Hot of limestone rocks in an ABS cylinder. A water is usually supplied by a boiler, but typical efficiency for a condensing boiler a domestic hot water heater has also is above 90%. been successfully used to heat the en- Boilers use a water or glycol mixture tire house. With a conventional boiler as their fluid for heat transport. Many setup, an indirect water heater is used homeowners opt for pure water due to to provide the domestic hot water. The its higher heat transfer capability, lower indirect water heater has heating coils viscosity (thus lower pumping costs) and within the tank, or an external double- lower cost, but glycol is recommended. wall heat exchanger to transfer boiler For domestic water connected systems, heat to the domestic hot water without food-grade propylene glycol must be danger of boiler water mixing with the used, and is quite expensive. Ethylene potable water. glycol is usually not recommended as it Boilers all operate on the same is a serious poison, but is the best freeze principles: water is moved through a protection for the money and contains large frame of steel or cast iron and an rust inhibitors. If a glycol with rust oil-fed fire burns around the heat ex- inhibitors is not used, a chemical such changer. When a thermostat calls for as “Stewart Hall 8-Way” or equivalent,

198 Chapter 8 containing chromate and sodium nitrate windows. However, with today’s well- should be used to protect the ferrous insulated homes and good windows, metal in the system. putting baseboard on interior walls can Efficiency and Controls: Boilers reduce heat loss through the bottom have minimum government-mandated of the wall and save energy. Since there efficiencies called the annual fuel uti- are different styles of fin tubes avail- lization efficiency or AFUE. This is a able, you should check the heat output, specific measure of efficiency developed which is usually rated in BTUs per foot by the government in 1987 but may not length of baseboard. This is especially fully represent the energy use required important if you are planning to use a to operate a boiler because it neglects lower-temperature heat source such as standby losses. Using a seasonal ef- a water heater or solar heated water. ficiency measure has proven to be a The distribution system should always better measure of efficiency for boilers. be slightly oversized above the house Seasonal efficiency provides a more -ac heating design load, though it is impor- curate apple-to-apple comparison of tant to size the distribution system on different boilers. Recent research by Dr. a room-by-room basis, and to not just Thomas Butcher at the Brookhaven Na- divide the total heating load by BTUs tional Laboratory has determined that per foot of baseboard. Use the resources AFUE actually can skew comparative at the beginning of this chapter for help efficiencies between different boiler de- in determining the design heat loads of signs. Dr. Butcher’s report may be found various rooms. at http://www.bnl.gov/est/files/pdf/ Radiant Floors have become the ButcherAachenPresentation.pdf Due to system of choice for most modern efficiency improvements, replacing an home-builders due to their comfort, inefficient boiler, even a fairly new one even heating, and low water tempera- with an AFUE around 70, can result in tures. Radiant heating in general relies energy savings of up to 25%. on heating the objects in a room rather One of the big benefits of hydronic than the air itself, which is more com- boilers is the ability to easily maintain fortable but also more efficient. Most different temperatures in different parts radiant hydronic systems employ plastic of a building through the use of zones. pipe in a poured slab or over subfloor- Zone valves allow one area to be heated ing in lightweight concrete or gypcrete. at a time, which reduces overheating Check the manufacturer’s specifications and enables heat to be moved efficiently for spacing needed for a given heat load over long distances. Extra large zones or and concrete thickness. zones very far away from the boiler may Plywood subflooring with radiant need their own circulating pump. tubing has been gaining popularity of Various controls and operating strat- late, and must be used with aluminum egies exist to reduce hot boiler operat- diffuser plates to spread and direct the ing standby losses. heat. In both installations it is necessary Baseboard fin-tubes are quick to to insulate under the heated floor. For install, fairly low-cost, (though rising wet (concrete) applications, heat may metals prices may change this), and easily be lost to the ground or ground- they are efficient. Traditional wisdom water, wasting money. In plywood-based said that baseboards should be installed systems, achieving the desired level of at exterior walls and under windows heat transfer of the building may neces- to maximize air circulation and re- sitate a high level of insulation below duce moisture buildup on and around the plywood, and heating of the crawl-

Heating and Domestic Hot Water 199 space will occur if the floor is not insu- Stand-by heat loss lated adequately. A radiant layer beneath Stand-by heat loss is the heat trans- the heating pipes should be installed, or mitted to the surrounding area of the a grooved-plywood product with built-in boiler room and convected up the radiant shielding should be used. chimney during the off cycle. Domestic Radiant floors use lower-temperature cast iron boilers have �⁄₂ inch of fiber- water, typically between 100-120º F. glass insulation on the sides and top This reduces standby losses at the boiler and none on the bottom. This minimal and keeps the floor from overheating. amount of insulation is not sufficient for Floor temperatures above 85 degrees a boiler that is operating regularly from result in discomfort and steps should 140° F to 200° F. There is not room be taken to keep the floor temperature between the metal cabinet and the cast below 85ºF. Radiant floors are typically iron sections to increase the amount some of the more expensive heating sys- of insulation. It is not unusual to enter tems, but should give life-long service if a mechanical room and find 80°+ F air installed correctly. temperatures. Most typical oil fired Radiant forced-air systems have been heating systems prefer a negative .02” of used in floors in the past, but these suf- water column draft over the fire, which fer from some of the same problems is maintained by the use of a barometric of control and inefficient blower fans damper. The warm air in the mechanical as poorly ducted forced-air systems room bleeds through the damper and up discussed earlier in this chapter. If de- the chimney continuously under these signed correctly, however, a forced-air operating conditions. In many small radiant floor could be comfortable and homes in rural Alaska, the stand-by heat make use of displacement ventilation to loss from the boiler will often over heat efficiently ventilate and heat a room. the living space, causing the unit to be For more information see http:// controlled by the service switch. eere.energy.gov/buildings/info/homes/ coolinghome.html Advantages of a Low Mass For a free program to assist you with modeling radiant systems, see: http:// Boiler windows.lbl.gov/software/therm/therm. Typical cast iron boilers have from html 6 gallons (50 lbs) to 15 gallons (125 lbs) Proper sizing of oil boilers can be a of water in them. That is in addition real challenge because there aren’t many to 400 lbs to 600 lbs of cast iron. This choices-the smallest are typically in large mass may be sitting in the mechan- the 75,000 BTU range. For this reason, ical room at a high operating tempera- as well as physical size and cost con- ture, waiting for a call for heat or a need siderations, some people have started for DHW. All the while it is radiating using domestic water heaters for space and conducting heat to surrounding heating and domestic dual-uses. Proper area while convection carries heat up sizing is important because cycling and the chimney. If the boiler uses a control standby (jacket) loss of boilers, especial- that does not maintain temperature for ly high-mass cast iron boilers, increases a DHW tank-less coil, the boiler may be with oversized capacity. cooled down to ambient (room) temperature. In that case on a call for DHW, 4 to 7 hundred pounds of water would need to be heated to bring the storage as well as reduce stand-by heat loss. A tank up to temperature. savings of 6% to 10% can be expected A low mass boiler works more like a by adding an outside temperature reset hot air furnace. The boiler weighs 250 control. A manual reset, over tempera- lbs and holds 2�⁄₂ gal (21 lbs) of water. ture trip is another very good option on Before a call for heat it is at ambient all heating units. Adding such a control temperature just like a hot air furnace. is like buying insurance and bolting it On a call for heat the burner and the to the heating unit. Should the regular circ pump start. Water is circulated temperature control fail, the over tem- from the supply to the return header of perature trip will shut down the unit the boiler. In approximately 90 seconds, before an unsafe temperature is reached. the return header is 170° F and the ener- The building occupant can restore heat gy manager opens the appropriate zone by pressing the red button (reset) on valve/s to satisfy the demand. Near the the over temperature trip. Repair or end of the cycle the burner is stopped replacement of the boiler temperature and the circulating pump continues to control is necessary to return the system run (just like the fan of a hot air fur- to automatic. In the case of a hot air nace) to purge the last of the heat out furnace, overheating will probably be of the boiler until it is back to ambient caused by a broken blower drive belt, temperature. There is very little loss to bad blower motor, or an obstruction in the surrounding area. Consequently low the return air to the furnace. This prob- mass boilers are not as disadvantaged lem would have to be corrected before when over-sized as are typical high mass heat could be restored. boilers. Barometric dampers are not used so very little warm air goes up the Domestic Hot Water (DHW) chimney. This process can make a 20%+ difference in fuel consumption com- Supplying DHW is a significant heat pared to typical high mass boilers. load in the modern building. In a super- insulated 5-star home, depending on oc- Boiler Controls cupancy, the DHW may energy use may equal or exceed the heating load. Build- Typical boilers have a control that ings with hot air heating systems fre- manages a boiler temperature suitable quently are equipped with electric water for the coldest mean temperature ex- heaters. This is not the best choice! The pected in winter. If the boiler has a tank- initial cost of an electric water heater is less coil, it may also maintain a mini- lower, but as a rule, electricity is a more mum temperature to insure adequate expensive option than fuel oil or gas. At DHW when there is not a call for heat. the time of writing, heating with elec- The control also doubles as a switching tricity will cost a family 69% more than relay to control the circulating pump heating the same amount of water with on a call for heat. These controls are re- a relatively new boiler. An office build- sponsible for much of the stand-by heat ing with no bathing, cooking, or clothes loss. After-market controls are available washing facilities could be a candidate that maintain the boiler temperature for electric water heating. As a rule, any as necessary depending on outside air use of high resistance electric appliances temperature. The outdoor reset control is discouraged, particularly in rural will lower the mechanical room ambient Alaska. There are many different types temperature which can make the home of domestic water heaters available; only more comfortable in warm weather, a few are described here, and not all

Heating and Domestic Hot Water 201 Table H-2 LIFE-CYCLE COSTS FOR DIFFERENT TYPES OF WATER HEATERS Water heater type Efficiency Cost¹ Annual en- Life (years) Cost over ergy cost² 13 years³ Conventional gas storage 57% $380 $337 13 $4,767 High-eff. gas storage 65% $525 $296 13 $4,373 Conventional oil storage 55% $950 $636 8 $10,165 High-eff. oil storage 66% $1,400 $520 8 $9,562 Conventional electric storage 90% $350 $792 13 $10,650 High-eff. electric storage 95% $440 $734 13 $9,986 Demand gas 70% $650 $302 20 $4,571 High-eff., pilotless demand gas 84% $1,200 $170 20 $3,406 Demand electric (2 units) 100% $600 $800 20 $11,000 Electric heat pump 220% $1,200 $271 13 $4,717 Indirect water heater with ef- 79% $600 $289 30 $4,357 ficient gas or oil boiler Solar with electric back-up n/a $2,500 $242 20 $5,640 • Approximate cost. Includes installation. • Energy costs based on hot water needs for typical family of four and energy costs of 16¢/kWh for electricity, $1.297/therm for gas, $3.15/gallon for oil. • Future operation costs are neither discounted nor adjusted for inflation. Source: American Council for an Energy-Efficient Economy. Energy costs interpolated to Fair- banks, Alaska in February, 2008

may be available locally. Here is a cost- nating the water heater. Thirty years breakdown of many different types of ago, this was standard practice and is water heaters, along with their expected responsible for many boiler sales. This longevity. process incorporates a �⁄₂” copper coil High mass cast iron boilers have with heat transfer fins that is submerged been marketed in Alaska for years, in the heating fluid of the boiler, and partly by promoting the “tank-less coil” domestic water circulates through the as an endless supply of DHW and elimi- coil on its way to the hot water faucet.

Figures H-1-3. Flat plate heat exchanger.

202 Chapter 8 lating pump to respond to the call for hot water. During the off cycle the boiler temperatures can cool down to ambient, which helps to reduce stand-by heat loss. Stor- age tanks with heating coils are relatively expensive, $700 to $1000 depending on size and manufacture. Not all Figure H-4. tanks have removable coils for cleaning. In the event the storage tank is depleted Figure H-5. It is advertised as an endless supply of of hot water (cooled to 80° F) the recov- DHW from 2 to 4 GPM (depending on ery time is approximately 35 minutes to boiler size) of water at the shower or get 120° F water to the faucet. sink. Boiler controls establish two dif- Another method of heating and stor- ferent temperatures as needed to supply ing DHW is to use an electric water DHW or heat the building as called heater for a storage tank. These tanks for. These temperatures would typically are well insulated, and must be ap- be around 160° F for heating DHW proved by the ASME (American Society and 180° F to 200° F for space heating. of Mechanical Engineers) as pressure Reading the fine print of the O & M vessels, and are relatively inexpensive, manual that comes with the boiler will ($250 to $300). The heat source can be stipulate that in order to produce the a tank-less coil side arm, or a flat plate DHW flow rate as advertised, the boiler heat exchanger. Flat plate heat exchang- must be at 200° F and the inlet water ers are usually the most efficient heat must be 40° F. This is seldom the case in exchanger available, and are recom- much of Alaska. This system as designed mended. Hot and cold connections are causes a tremendous stand-by heat loss made to the normal connections on top as the boiler is standing-by at a high of the tank. The same pressure and flow temperature continuously in order to rate can be expected in the hot and cold provide the hot water on demand! service lines. A plastic tube inside the Several alternatives to utilizing the tank will carry the incoming cold water tank-less coil are available. One method to the bottom of the tank. Cold water is to simply use a DHW storage tank. will be pumped from the bottom of the One storage tank method that is gain- storage tank though a heat exchanger, ing popularity is the “coil within a tank”, and returned to the top. The water will some times called a “Boiler Mate”. stratify as the heated water rises to the These tanks are insulated well and have top. This method of heating and storing minimal heat loss to the surrounding DHW allows nearly the whole tank of area. This is an old method of heating water to be used before the next heat- and storing DHW that was originally ing cycle begins. When the tank is down used in hotels, apartment buildings, to about five gallons of hot water, the and other commercial buildings. This circulating pump starts and makes up method of supplying hot water allows water at about three GPM. A minimum the DHW tank to be just another heat- number of heating cycles are required ing zone by using a zone valve or a circu-

Heating and Domestic Hot Water 203 but hot water is always available at the ing place in the storage tank, the tem- faucet. perature sensor is disabled by cutting it off at the bottom of the valve. Installing a Domestic Hot 6. Tanks that have the T/P relief on Water Storage Tank the side of the tank will have a tee installed near the port to receive the efflu- 1. Select a super-insulated, electric ent from the domestic water heater as hot water heater to be used as a stor- well as the relief valve. age tank. A tall skinny tank instead of a 7. Tanks with the T/P relief port on short fat one, is preferred, because this the top, should have a short plastic tube will enhance stratification between the approximately 12 inches long installed in hot and cold water. A 30 to 50 gallon ca- the tapping to carry the hot water from pacity is usually adequate. the heater a short distance from the 2. The tank should be set on a stand hot water supply to the home. This will 3 to 4 inches off the floor to allow for prevent short cycling of hot water and air circulation, preventing condensation possible scalding. and corrosion. 8. Install a circulating pump with 3. Domestic supply and return lines around three GPM capacity. A March are connected to the normal connec- model 809 or Taco 003 is adequate. The tions on top of the tank. pump should be isolatable (valved on Figure H-6. Here is an 4. Remove and dispose of the water both sides). example of a low-cost heater drain valve connection from the 9. The pump should be controlled by electric water heater tank. Using brass or copper fitting only, a switching relay that has auxiliary con- that has been converted provide a hose bib for a tank drain and tacts such as a Taco SR 501, RIB 2401D to a boiler-mate using a supply line for a small (3 to 5 gpm) or Honeywell R889A or equivalent. the side-mounted heat bronze or stainless steel circulating The thermostats originally intended exchanger. pump, like a Taco 003 or equivalent. for the heating elements of the electric The circulating pump will pump cold water heater can be used to operate the water from the bottom of the storage 2401D, SR 501 or R889A switching relay. tank to the tank-less coil, shell and tube, (The Taco SR501 and the Rib 2401D or flat plate heat exchanger. will require a separate 24V power sup- 5. Remove the pressure/temperature ply.) The top thermostat will trip the (T/P) relief valve from the top of the relay to start the circulating pump and tank. Since there will be no heating tak- heat the top part of the storage tank. When the top thermostat is satisfied C H and opens, the bottom thermostat will hold the relay closed through the aux- T/P Relief iliary contacts until the entire storage Storage Tank/ Valve Tankless coil or tank is hot. (Note: The bottom thermo- Elecctric Heat exchanger stat and the auxiliary contacts cannot Water Heater trip the relay.) Only the 24V control power will be connected to the storage R889A tank. or equal RIBT2401D Solar DHW Tank/ March 900 Boiler Stand Taco 007 Bronz Despite our cold climate, we here in Grundfos Ss Alaska do get quite a bit of sunshine. or equal According to data from NREL (the Figure H-7.

204 Chapter 8 National Renewable Energy Lab) many places in Alaska are comparable to locations in the lower 48 for annual solar energy. Alaskans have used solar DHW successfully for many years. Proper installation requires the use of an anti- freeze solution to circulate in the solar collector loop, so that it is always pro- tected from freezing. This is only a brief mention of solar DHW; for more information, get the Cooperative Extension’s A Solar Design Manual for Alaska. The other options have exclusively, except perhaps for wood, required an outlay of money for fuel. Solar hot water systems are more expensive to install than other options we’ve described, but Figure H-8. their fuel is free. Thousands of gallons of equivalent diesel in the form of solar energy fall on the roof of the average Alaska residence every year in the form of sunlight. The proper installation could save thousands of dollars worth of fuel costs over its lifetime. The only drawback is that most of this solar energy comes in the summer, with very little sunlight arriving during the winter, and therefore DHW needs must be fulfilled by another source during the coldest three months of winter.

References

1Rutkowski, Hank. Manual J: Resi- dential Load Calculation. Air-Condi- tioning Contractors of America, 2001. 2Rutkowski, Hank. Residential Duct Systems, Manual D. Air-Conditioning Contractors of America, 1995. 3Lekov, Alex et. Al. “Residential Two-Stage Gas Furnaces-Do They Save Energy?” Lawrence Berkely Labs. 2006. Available online at http://www- library.lbl.gov/docs/LBNL/598/65/PDF/ LBNL-59865.pdf.

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