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Using forced air fan for cooling

We live near Seattle, where the summers are enviably temperate. However, we usually have a handful of days each summer where the temperatures spike into the upper 80s and even into the 90s. Because we only suffer for small periods of time, A/C is just not a viable option (though ask me on a day like today, and I'll tell you money should be no object when it's this hot!). We just set up our furnace to let the fan run to help move air throughout the house. I'm hoping this will make the house more comfortable on our rare hot days in one of two ways: a) the air intake is located in the basement, which is considerably cooler and which would make the air blowing out the registers likewise cooler, and b) because just creating air flow can make a hot room more comfortable, rather than letting the air sit stagnant.

Does anybody have any suggestions on what I should do to maximize the performance of the fan? Specifically, I want to know whether I should leave windows open or closed? When and how long should I run the fan? I haven't figured out whether our electronic programmable thermostat will actually control the fan, since I don't expect the temperature to really fluctuate in order to trigger the thermostat.

Re: Using forced air fan for cooling

Here are a couple of thoughts. For my credibility, we're spending our first summer in this old, three-storey house, had it insulated last fall, have new or relatively new windows with UV films, a new furnace, a programmable thermostat, no A/C.

First, to answer your thermostat question, I doubt it will activate/deactivate the fan without a temperature change.

However, we didn't turn on our furnace fan at all during a recent 10-day period in the 80's and 90's. Instead, we opened up the house every night, especially making sure that basement and attic windows were open as well as doors between floors. This would help the house to act like a chimney and vent all the warmest air out the attic windows.

In the morning, as soon we woke, we closed up every window/window shade/curtain on the south and east side, leaving shaded windows open until the temperature outside rose above the interior temp and/or the sun swung around and began to shine in.

We ate a cold breakfast and lunch, and grilled outside for dinner, and took quicker-than-usual showers, closing the bathroom door and opening the window to let the steam out. The refrigerator was the only interior source of heat.

Late afternoon, we sometimes needed a room fan to simply circulate interior air in the room we were using to keep it comfortable.

Near the end of the 10 days, the inside air got as high as 74-degrees because the plaster/wood/furnishings were starting to warm during the day and hold heat at night. For the most part, the house started at about 66- or 68-degrees each morning, and only rose two degrees throughout the day.

Next year, window awnings are in the budget and I intend to install a high-speed exhaust fan in the attic window.

Good luck!

Re: Using forced air fan for cooling

I agree that keeping the windows closed along with the window coverings during the day helps from keeping the heat out and
opening them at night to let the cooler air in.

As for the furnace fan run it as you feel you need to and for as long as you like.


First, to answer your thermostat question, I doubt it will activate/deactivate the fan without a temperature change.

If the fan is switched to the "on" position on the thermostat is simply manual switched. It won't turn on or off with any temperature change or work with any programming.
It will run when it's turned "on" and continue till it's switched to "off" or "auto".

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