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Heating & Air Conditioning

Understanding your forced-air furnace

During normal operation, the burner on the furnace starts up, warming the heat exchanger and the air in and around the heat exchanger. When the air is warm, a fan control starts the fan to distribute the warm air into your home. This delay is built in so the fan does not start immediately and blow cold air on your feet.

When the room air near the thermostat is warmed to the set point, the thermostat turns the burner off. The fan continues to run until it has removed the heat from the heat exchanger. When the heat exchanger is cool, the fan limit control turns the fan off.

Occasionally, the fan may start up again within a few minutes and cycle for another 40 seconds or so. If this is the case, your fan control limit switch is set to such a low temperature that it senses residual heat in the metal of the heat exchanger, so it re-starts the fan.

This low setting helps utilize all the heat in the heat exchanger. It does cause some extra wear and tear on the fan, but that should not be a major concern. A heating contractor can adjust this control so the fan does not start a second time, but then you will lose some heat.

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High-efficiency gas furnaces feel cooler

High-efficiency gas furnaces discharge cooler air into living spaces compared to older furnaces. You’ll get used to the cooler temperature, and the energy savings of up to 40 percent should help “temper” your feelings toward the new fu rnace. Because your new furnace is more efficient, you may wish to raise the temperature setting a few degrees, allowing more comfort at little additional cost.

The discharge temperature is lower because the furnace uses almost all of the available energy in the gas it burns. This lowers the temperature that’s required to transfer heat from the products of combustion into the air circulated in your home.

You may feel a draft as this cooler air discharges at a greater speed from the supply duct grills. If this draft is a major problem, consider installing a plastic air deflector to redirect the air discharge. If air is not directed toward your skin, you will not feel a draft.

Another possibility: ask your heating contractor to check that the furnace and the fan speed were set up properly. If you notice a draft at one particular register, the contractor can lower the flow to that register.

Some top-of-the-line furnaces also have variable-speed fans and variable heating rates to adjust for this “draft” problem. Have the contractor make sure that all the settings are correct.

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When a high-efficiency furnace stops producing heat

Furnaces vented with plastic pipes can have simple but serious “no heat” problems in the winter. If snow or ice blocks the plastic pipes, the furnace will not run. Keep the vent pipes clear, and check them if your furnace will not run. If the pipes are packed with snow or frost, use a hair dryer to thaw out the buildup.

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Heating and cooling adjustments-forced air furnace

Warm air rises; cooler air sinks. Keep this principle in mind, and you’ll realize why opening the correct air returns in winter and summer will provide better air distribution-which, in turn, allows more even temperatures in your home.

When you use a forced air furnace for summer cooling, you should open the high returns. This allows the furnace to take warmer air from the top of the room back to the air conditioning cooling coil in the furnace. In the winter, open the low returns to collect cold air at the floor.

For a two-story home, you may also need to adjust the supply air for winter and summer. In the winter, warm air rises to the second floor, so less heating is required there.

In the summer, warm air still rises, and a hot attic adds even more heat, so you need greater cooling (air flow) to the second floor than to the first floor.

The best way to control air flow is to adjust the small dampers in the heating/cooling duct system in the basement. Often, these dampers are found where round supply duct runs connect t o the main (rectangular) ducts. Look for small (¼-inch) threaded rods and wing nuts. You can adjust the damper by turning the screwdriver slot on the small rod. When the slot is parallel to the duct, the damper is fully open. You don’t need to adjust the wing nut, which simply locks the rod into place.

Heating ducts vary. Some systems have levers indicating the direction of the damper. Some rectangular ducts have dampers and levers.

To adjust air flow for summer cooling, start by fully opening all second floor dampers. Next, partially close dampers to first floor rooms that are getting lots of cold air. You will find that closing the damper to 50% or turning the shaft to 45 degrees will only partially slow the air flow. Often, even if you fully close the damper, there will still be air flow because the dampers fit very loosely in the ducts.

Closing first floor dampers will direct air to the second floor. rk your damper settings for summer and winter once you have found the correct balance.

Remember to clean the furnace filter, too, because a plugged f ilter can also restrict air flow.

Older homes were not built for cooling-the supply and return ducts to the second floor may not be adequate-so adjustments may not solve the problem. A quick fix may be to run the fan furnace continuously.

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Furnace air filters and maintenance

How often should you change the filter on the furnace? Whenever it’s dirty. And although it sounds a little silly, better filters get dirty more quickly and need to be changed more often.

A standard cheap (about $1) fiberglass air filter should be checked once a month and changed when it shows visible dirt. You also need to check the filter when running the central air conditioner, because air circulates through the furnace and the filter.

I suggest you replace the cheap fiberglass filter with a pleated paper filter. You will find them in any hardware or building supply store next to the standard filters. Read the labels-some are more efficient than others. Price will vary from about $3 to $15. These filters will trap much more dirt and smaller particles of dirt. They need to be changed more often because they do a better job of trapping dirt.

The next level up from standard throw-away filters are washable filters and electrostatic washable filters. Washable foam filters work quite well if coated with a special sticky spray like Filter Coat. Electrostatic filters are relatively expensive (about $100), but they do trap dirt well.

A better filter is the 6-inch-thick pleated paper filter. Air is forced through a long accordion of filter paper. Fine holes in the paper trap small particles of dirt. The large surface area limits pressure loss in the heating system. A special frame needs to be installed in the duct work, and the filter costs about $25, but it will last one or two years.

The top of the line is an electronic filter that charges metal plates in the air stream and attracts dust. This is the only type of filter that actually removes smoke particles from the air. This filter costs about $700 installed. Filter plates must be washed monthly in the dishwasher or by hand with soapy water.

I consider the pleated paper filters a good investment. The more expensive electronic filters are great for people with allergies or sensitivity to dust.

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Service requirements for older furnaces

If your warm air furnace is old (say, 20 years or older), I suggest you have a professional heating contractor servi ce it every year. This is your best protection against carbon monoxide dangers and heating problems. Routine service will also ensure peak efficiency to save you operating costs.

A good service and inspection costs about $80 and should include a complete cleaning, safety check, and tuning.

The service contractor should:

  • clean the burner and heat exchanger, and inspect for cracks.
  • remove the burners, clean them, and tune for proper combustion.
  • perform a carbon monoxide test in the heat exchanger.
  • check the vent pipe and draft diverter.
  • inspect the chimney for obstructions and draft.
  • check vent pipes for proper clearance and materials.
  • test fan controls and safety controls.
  • check the thermostat.
  • run the furnace through a complete cycle.
  • check flame roll-out.
  • check gas pressure (if appropriate for your furnace).
  • clean and adjust the pilot light assembly.
  • inspect gas fittings and repair any leaks.
  • lubricate the fan and motor.
  • check belt condition and tension.
  • service the filter.
  • clean the fan and housing if excessive dirt has accumulated.

Replacing parts or cleaning extensively will cost extra.

You should have a basic understanding of how the system works, so ask the service contractor to explain the basics. You should routinely service the filter and lubricate the fan and motor a second time during the heating season. You should also inspect the flue connection to the chimney.

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Noises from the heating/cooling system

You may have noticed unexplained noises from your central heating/cooling system. What causes them, and what can you do about them?

A typical problem: when the air conditioning starts, there is often a loud “pop” from the ductwork. This may not occur when the furnace switches on.

When the central air conditioning runs, the furnace fan must move more air through the system than when the unit is used for heating. Often the fan will automatically run at a higher speed for greater volume and pressure.

Because of this increased pressure, the duct work is more likely to pop outward slightly. You can locate the problem area by listening for the sound and watching the ductwork when the air conditioner starts up. You’ll probably notice movement and sound in the large, flat pieces of sheet metal near the furnace.

When you find the duct that is moving or popping, reinforce it with a small brace-screw a l ightweight angle iron into the sheet metal over the part that is moving.

Now, how about noises you hear from your forced-air furnace? When the heating system starts and runs for a few minutes, there is often clicking and slight pounding of the ductwork in the basement.

This problem occurs as the metal ductwork heats up. The expanding metal needs room to move. The ductwork is trapped between the framing members of the house. Watch and listen for the problem area(s) as the furnace runs. You may need to loosen mounting brackets or adjust ductwork that is forced against wood framing.

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Use your windows to help your air conditioner

Storm windows work as well in the summer as they do in the winter. Closing your storms will reduce the gain of heat through the windows and will also help stop infiltration of hot air. If possible, close shades and blinds to block direct sun.

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Central air conditioner, part 1: to cover or not to cover?

Your central air conditioning unit consists of a compressor and condensing unit placed outdoors in a metal housing. These units, built to resist the weather, generally do not need a cover. In fact, covers can cause problems because they trap moisture and create an inviting winter home for small animals.

Professionals who service the units tell me that most of the damage they see in spring was caused by rodents living in the units and chewing on wiring.

If your air conditioner is subject to falling ice or other debris, you could cover its top with a piece of plywood, plastic or metal held in place by a weight.

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Central air conditioner, part 2: seasonal shutdown and restarting

Central air conditioning systems are relatively maintenance free, but you do need to take several precautions to prevent problems.


In autumn, when the cooling season ends, turn off the power to your air conditioning unit either at the circuit breaker or at the electrical disconnect near the unit. This saves energy by turning off a small crankcase heater inside the unit. Thus, your air conditioner will be less likely to attract small animals during cold weather.

Turning off the power also prevents accidental s tarting during the winter, which could ruin the compressor.


In the spring, follow these steps:

  1. If you placed a plywood cover on the unit the previous autumn, remove it now.
  2. Check that the coils and fan are clean. If necessary, clean them with a hose and a soft brush. Make sure that the main power to the unit is still turned off when you do this.
  3. Inspect the unit. It should be level. Plants must not obstruct air flow; they should be 12 inches from the side of the unit and 36 inches from the air discharge.
  4. The outdoor temperature should be 65 degrees or higher for 24 hours before you operate the unit.
  5. Turn on the power to the unit at least 24 hours before operating the system. This gives the crankcase heater time to warm up the unit if needed. The heater warms the compressor crankcase, ensuring that oil is separated from refrigerant. When you turn the power on, make sure the thermostat control is set to keep the air conditioner off, because running the unit in cold weather can ruin the compressor.
  6. Central air conditioning will drain water from a pan in ductwork above the furnace, so check that the hose is clear and directed to the floor drain.

The central air system is a big investment. If you have any doubts, have a professional service the unit and walk through the start-up with you.

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What does a “ton” of air conditioning mean?

When dealers and contractors talk about “tons” of cooling in central air conditioning systems, what do they mean?

The term came into use when engineers developed standards for measuring mechanical cooling capacity. At that time, ice was commonly used for cooling. Engineer Joe Cool decided that cooling capacity measurements should relate to ice melting.

The standard was set equating one “ton” of cooling to the amount of energy needed to melt one ton (2000 lbs.) of ice over a 24-hour period.

For the technically competent, the exact figure for one ton of cooling is 12,000 Btu per hour. (Btu stands for British thermal unit, a measurement of heat or energy.) When ice changes from solid to liquid, the change of phase requires 144 Btu per pound or 288,000 Btu per 2,000 lbs. When melted in 24 hours, the 288,000 is divided by 24 hours and equals 12,000 Btu per hour.

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Rerouting a hose that drains your heating/cooling system

Let’s say you have central air conditioning and a high-efficiency furnace. Both of these produce water that drains through a flexible tube extending way across the basement to a floor drain. You’re worried that someone might trip on the hose. How can you fix this hazard?

You can’t totally eliminate the hose, because the water must be drained. But you can re-route the hose overhead, then drop it down to a laundry tub or floor drain.

To do this, you’ll need a small pump and container unit specifically designed for condensate. Its water tank-about the size of a large lunch bucket-is placed next to the furnace. As water collects, a 110-volt pump inside the tank automatically pumps the water out to any proper water receptacle.

You can purchase this equipment from a heating/air conditioning dealer. You will need to route the hose into the small tank, install the drain line, and provide a 110 volt (standard) outlet near the pump.

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Reducing severe dampness throughout the house

During winter, some homes have problems with excessive moisture. It’s most noticeable as condensation (“steam”) on windows. If moisture is excessive and stays on your windows for several days, if water runs off windows and damages wood surfaces, if ice forms on windows and frames, or if storm windows remained fogged up and icy all winter, you need to reduce the humidity level inside your home. Condensation requires a cool surface and moisture in the air. Inside your home, when the temperature of the glass drops below the dew point of the inside air, invisible water vapor in the air condenses on the cool glass. More condensation occurs when there is more water vapor in the air and/or when glass surfaces become colder. Evaluate changes you have made to your home-any effort to tighten up a home and reduce air infiltration will increase humidity levels. A high-efficiency furnace vented with two plastic pipes draws combustion air from outside and reduces ventilation. Weatherstripping, better windows, caulking, and any other measures you have taken to reduce air leaks will increase the amount of moisture retained inside your home. Try to increase ventilation by running kitchen and bath exhaust fans whenever steam is produced by cooking or bathing/showering. In the bathroom, keep the fan running until the bathroom is dry. Add timer switches to the fans if necessary. Limit the number of plants in your home. Look for plumbing leaks or damp areas in the basement. If basement crawl spaces have bare soil, cover the soil with a vapor barrier. There are many other sources of moisture and ways to eliminate excess moisture. Often your local natural gas utility company c an provide information on moisture problems. University extensions often have good booklets on solving moisture problems.

For a detailed analysis of moisture problems, please see Featured Articles and Books for “Fogged up? Clearing the Air About Window Condensation.”

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Reducing basement dampness in the summer

There are several ways of reducing dampness in your basement during the summer.

If you have central air conditioning and the supply/return ducts are connected to the basement, you can air condition the space. This will remove humidity and will mix basement air with overall home air. There will be a marginal cost for this, but the basement is cool already, and most of the energy will go toward removing the humidity.

If you don’t have air conditioning but there is central hot air heat and ductwork connected to the basement, you can run the furnace fan to ventilate the basement. Mixing the upstairs air, which is drier, with the basement air will help dry out the basement. This is an inexpensive option.

If there is no ductwork in the basement, consider opening basement windows on dry days to ventilate the basement. Open at least two windows and run a fan in one of them to speed up the process. When it is very humid outside, close the windows.

Your final option is to run a dehumidifier in the basement. In this case, do not ventilate the basement; allow the dehumidifier to remove the moisture. A dehumidifier works by moving moist air across a coil (similar to an air conditioner) where the moisture condenses into liquid.

Remember that mechanical refrigeration with a dehumidifier is relatively expensive compared to natural ventilation. It takes almost 1000 Btu to condense one pound of water from water vapor. This can be more expensive than running a refrigerator.

I prefer to open the windows and use natural ventilation. This allows the basement to air out so that it smells like the great outdoors.

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Heating a basement recreation room

The best heating system for a basement recreation room is a connection to the central forced-air heating system. This provides both heat and ventilation.

However, a common problem is that the basement remains about 10 degrees cooler than the rest of the house. A l ittle supplemental heat is in order.

During sunny, cool weather, as the first floor experiences heat gain from windows, the furnace will not run. This makes the basement area cooler because it needs a small amount of heat but has no gain from windows. For a quick solution, try running the fan on the central system. This will bring warmer air to the basement.

The best solution is to add supplemental electric resistance heat in the basement room. This could be a portable heater or permanently mounted baseboards. Either will work.

The advantage of the electric heat is you can run it only when you need it. You will also find that it takes little additional heat to warm the room because the basement has little heat loss. Once it is warm, it will stay warm.

Before you add electric heat, check any existing heating ducts (for instance, for a finished basement room, you may have added ducts that extend from the existing ducts). One duct should be a supply and one should be a return. Add a return if you don’t have one-it is hard for your furnace to blow air into a sealed box. You could also adjust the dampers in the ducts to direct more air into the basement.

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Excessive winter dryness indoors

Humidification of air inside the home has been the subject of many articles and investigations. Manufactures of humidifiers have claimed that humidified air would protect us from health hazards, but there are no firm facts that humidified air is better for us. In fact, humidifiers can cause problems with excessive moisture and even mold or bacteria.

To decide on the need for a humidifier, evaluate the comfort of your home during the dead of winter. Many of today’s tighter, energy-efficient homes don’t need additional moisture. Condensation on windows indicates excessive humidity; in that case, you don’t need a humidifier. However, if your nose and skin are dry, and static electricity is a problem, you may need a humidifier.

The best type is a central humidifier that mounts on a forced-air furnace. Look for one that flushes water over a panel and drains away excess water as it operates. It should be mounted on the return duct to prevent water leaks into the furnace, and it should have a humidistat control that automatically turns on the unit as needed.

Aprilaire is a quality brand of furnace-mounted humidifier. Its newer models have a removable plastic cover that makes the unit easy to maintain. This type flushes water over a panel and doesn’t require a water reservoir.

Portable humidifiers can operate with a reservoir and evaporative panel. To create mist, some use ultrasound, others use a spinning wheel (for a cool mist), and others use heat (making steam). I co nsider all of these types hard to maintain and difficult to control. Any unit with a water reservoir is a potential source of mold or bacteria and must be meticulously cleaned and disinfected on a routine basis.

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