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Is Your Heating System an Energy Beast?
comments (0) March 16th, 2009 in Blogs
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Drawing by: Jackie Rogers
by Dave Yates
The economy is down, fuel costs are up, and chances are that your heating budget is already busted. You need to do something—but what? Only a few of us are ready to invest in geothermal or solar. The rest of us need to find the answer in the heating system we already have.
For 70% of U.S. households, that system consists of a furnace that forces hot air through ducts; for 17%, it’s a heat pump; and for 11%, it’s a boiler that heats with water or steam radiators. The remaining 2% of homes use wood, coal, geothermal, solar, or other heating methods. When it comes to fuel, 58% of us use gas (either natural or propane), about 35% use electricity, and almost 7% use fuel oil.
Your home might not have the most efficient heating system available, but there’s good news: You can tune up your current system so that it performs better, keeps you more comfortable, and doesn’t put as big of a dent in your wallet. How? The Q&A below can help.
Although the topics might seem simple, they’re useful in diagnosing deficiencies. In fact, I usually end up fielding a lot of these questions from homeowners based on their observations of how their heating system is or isn’t working. Once you know where your system is falling down, it’s possible to boost it (and its efficiency) back up.
I'll start with a basic explaination of the way each system works, then I'll answer your burning questions.
| Furnace Basics |
Furnaces use natural gas, propane, oil, or electricity, and are fired when a remote thermostat detects that the temperature in a room has fallen below a preset level. Once in operation, the burner fires in a combustion chamber and warms a heat exchanger (electric furnaces have coils much like a toaster). A blower pushes air over the heat exchanger, or coils, and hot air flows through a series of ducts and enters a home’s living spaces through registers in the floors, walls, or ceiling. Ducts also supply return air to the furnace, and combustion gases exhaust through a chimney or direct-vent system.
Q. I hear a whistling noise around the blower compartment of my furnace. What is causing the noise? Should I be concerned?
A. You’re hearing air leakage. All air handlers (any device with a blower, including furnaces, heat pumps, and central air) have two ducts: one for supply, the other for return. I often find considerable air leakage at both connection points. If the blower is located in an unconditioned location (attic, crawlspace, or basement), it is bleeding out heat, or Btu, on the supply side while pulling in unconditioned air that must be warmed (or cooled and dehumidified) on the return side. This energy loss can add 10% or more to your heating and cooling bills.
You can fix these leaks by sealing the connection with sealant and/or top-grade mastic tape rated to withstand the area’s exposure. While you’re at it, check the air handler’s access door, another frequent source of air leaks. Because the access door must be opened to service the equipment, you want to use only tape or magnetic strips to seal gaps. Other spots to seal include filter slots and openings for wiring. Last but not least, the accessible ductwork should be examined for leaks. Seal them with high-quality tape, mastic, or sealant that’s compatible with the duct material and with exposure to surrounding air temperatures.
| Heat-Pump Basics |
Air-to-air heat pumps use pressurized Freon gas to absorb heat from the air outside and transfer it to your home. When the thermostat calls for heating, Freon is pressurized, it condenses, and then it turns to hot liquid. A blower forces air across warm Freon-filled coils and through a system of ducts; warm air is distributed through registers in the floors, walls, and ceiling. At the same time, a fan in the condenser sends cold air outside. You can reverse the cycle for cooling in the summer. (Ground-source heat pumps use a water/glycol mixture to exchange heat energy with the earth.)
Q. The temperatures upstairs and downstairs are uneven; some rooms are colder or hotter than others. What's causing this problem? Can it be fixed?
A. You're likely describing an out-of-balance duct system. If a forced-air system isn't ducted properly, the flow of supply and return air is unbalanced, resulting, for example, in a ground floor that doesn't stay warm in heating season or a second floor that's not sufficiently cooled in AC season. Sometimes it's due to poor duct design; other times it occurs when air-conditioning is added to a heating system without re-evaluating and possibly resizing the ductwork.
If you have problems with individual rooms and you've made sure all the ducts are connected properly (believe me, I've seen my share of ducts to nowhere), you might be able to adjust the dampers and guide a little more (or less) air to those areas.
Dampers are normally located within the first few feet of each branch, or takeoff, and are adjusted by turning an external lever.
Generally, when the lever is in line with the duct, the damper is fully open. Airflow also can be regulated somewhat at the register if it's an adjustable model; however, that can create an objectionable noise as air rushes past the louvers.
While adjusting airflow this way could improve comfort, it doesn't help the system to perform better. To do that, you need to call in a pro. A good HVAC contractor uses a nationally approved design program to size an entire duct system properly. Ask the contractor to show you how he or she does the design work, and ask questions. The fix can range from a few simple adjustments to installing a mini-split inverter heat pump in the affected areas to ripping out everything and starting over, costing from a couple of hundred dollars to several thousand.
| Boiler Basics |
Boilers heat water with gas, propane, oil, or electricity, and the water heats the home through a hydronic delivery system that can include baseboard fin-and-tube radiators, steam radiators, or in-floor radiant heating. When the thermostat fires the boiler, fuel burns in a combustion chamber, and warm water is pumped through a closed circuit of tubing. (Electric boilers have direct-immersion heating elements.) The water can get as warm as 180°F, depending on the system’s design. Because hot water expands, a pressure gauge and a relief valve prevent the system from failing due to excess water pressure. Combustion gases exit the house through a chimney or a direct-vent system.
Q. What separates low-efficiency heating systems from high-efficiency models?
A. One difference is the way the unit is vented. A 78%-efficient furnace (or boiler) vents into a chimney and uses the home’s interior air for combustion. New 92%-efficient models are designed for sealed combustion. A direct venting setup draws outdoor combustion air.
Chimney-vented heating equipment continuously drafts heated air out of the house and strips away some of the Btu produced when the furnace is operating. There’s also a hidden energy cost: air infiltration. Whenever its burner fires, the chimney-vented unit draws in warm room air to support combustion—air that must be replaced by cold outside air drawn through cracks and gaps in the home’s shell. Eliminate that draw with a sealed-combustion model, and your fuel bills could fall by 30% or more.
Cost also separates the top performers from the rest. But the difference in price between 78%- and 95%-efficient gas-fired furnaces has narrowed considerably, to about $1500 for the equipment and installation costs. If your system burns oil, you have fewer choices, and the price gap is wider (about $4000). But with ever-shifting oil prices, it’s easier to justify the extra expenditure.
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—Dave Yates owns and operates F.W. Behler Inc., a mechanical contracting firm in York, PA.
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posted in: Blogs, energy efficiency, hvac, plumbing
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