Let Your Forced Air Furnace Do It's Work

by Warren Cook


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Dear Energy Adviser:

We have a new two-story home with a gas forced air heating system and a gas fireplace. This winter, I've noticed the upstairs hallway is a lot warmer than the living area below. We set the heat back at night, and the two bedroom doors upstairs are usually closed. We run a ceiling fan in the two-story entrance stairwell. What can we do to even out the temperature?
E. L.

E. L.
New houses are more resistant to drafts because the building shell is sealed better than older homes. Extensive caulking around wiring holes, openings for windows & doors and wall framing, plus better quality window and door weather-stripping and tighter siding, has made new houses so snug that a lot of the "natural" air movement we used to take for granted doesn't happen. Less drafts means that the natural (uncontrolled) flow of air through the building has been reduced. We have to rely on the heating system to move the air in the home, because the leaks have been plugged up. In order to maximize comfort, we need to let the heating system do its job. Practices we have grown accustomed to -- to save energy -- can often reduce comfort. We need to find a balance of thrifty operation and personal comfort.

One habit that's hard to break is night setback of the thermostat. However, if it's comfort you seek, the furnace needs to run. Maybe a temperature somewhere in between the day setting and the night setting will work for you. I know this sounds contrary to the "put on a sweater" conservation ethic, but comfort should be a factor in all energy decisions. You don't want to be wasteful, but you should be comfortable.

In your house, the forced-air furnace blows heated air to rooms through the ductwork. The heated air from the furnace register -- the grille where the heated air comes into the room -- mixes with the cooler air in each room until the overall temperature is the same as the thermostat setting. Registers are often on outside walls so they can mix heated air with the cooler air near windows and exterior surfaces in an effort to balance the room temperature. The room air circulates back to the furnace to be re-heated by drifting to a return grille -- usually a large opening in a hallway ceiling. The furnace is happiest with return air that doesn't need a lot of heating, and a leak in a return duct that allows outdoor air into the system can reduce the system efficiency.

Closing of rooms prevents adequate return air from getting back to the furnace. Energy experts have long told us to close off unused rooms to save energy. However, closed off rooms won't save energy unless the furnace registers in those rooms are also closed. An open register in a closed rooms is triple trouble: the heated air supply tries to pressurize the room and forces heated air out cracks and leaks, the reduced circulation from the closed door prevents the room from reaching correct temperature and the closed door "starves" the return duct of a percentage of the air it needs to keep the rest of the house comfortable (see Energy Adviser 2/7/99.) Closing off too many registers throws any forced-air system out of balance -- if the supply air flow and the return airflow are equal, the system is balanced.

The ceiling fan in your hallway mostly stirs the air in the fan's immediate area and can't do an effective job guiding air back to the furnace. Another drawback to ceiling fans is the coolness felt beneath them from the moving air. To maximize comfort and keep the furnace airflow balanced, many folks run the furnace fan all the time. Most furnace fans are fairly quiet and a constantly running fan becomes part of the home's background noise. There's an energy cost to running the fan all the time. A 400-watt furnace fan costs about $13.50 per month to run in Clark County, so comfort has a price. If this cost is more than you like, you could run the fan part of the day, maybe turning off the fan when you set back the heat at night.

Turning the heat way down at night can wreak havoc with overall comfort. If you are looking for even temperatures, let the furnace work less to balance out the various rooms. Find a temperature setting you like and stick with it, open up those bedroom doors and registers and let the furnace keep you comfy.


Warren Cook is an energy consultant for Clark Public Utilities. You can send questions to energyadviser@clarkpud.com or to Energy Adviser, in care of Clark Public Utilities, P.O. Box 8900, Vancouver, WA 98668. A panel of local energy efficiency and energy product experts will answer your questions.

This article originally appeared on the Clark Public Utility District website clarkpud.com

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