# Central heat/air fan only on **URL:** \ **Category:** In My Humble Opinion\ **Created:** [October 29, 2015, 1:50am UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036 "2015-10-29T01:50:10Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [October 29, 2015, 5:16pm UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/21 "2015-10-29T17:16:36Z")
> [@Amateur\_Barbarian](#): > > Not if there’s nothing driving the exchange. Opening windows on a hot, still day will do very little to “freshen” the inside of the house. Have you ever opened a window? Open at least 2, on opposite sides of the house. And, the only reason to even do this is if the outside air temperature is more favorable - such as during this season, where it’s not uncommon for the outside air to be cooler than it is inside but not too cold to be habitable. The goal isn’t to “freshen” anything, it’s to make the interior air temperature more comfortable without paying to run the compressor, which consumes something like 8000 watts of power for a 5 ton. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [October 29, 2015, 5:34pm UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/22 "2015-10-29T17:34:23Z")
> [@Habeed](#): > > All the previous posters are wrong… Re-visit post number 13 please. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [October 29, 2015, 5:38pm UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/23 "2015-10-29T17:38:13Z")
> [@kanicbird](#): > > Re-visit post number 13 please. It’s wrong. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [October 29, 2015, 6:05pm UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/24 "2015-10-29T18:05:25Z")
> [@kanicbird](#): > > It will bring in fresh air due to the pressure difference and the open window. In the place where the air is sucked into vents that will be a negative pressure so will suck in air from outside. The far rooms will have positive pressure and will have air escape out the windows. If you close those doors, build up more positive pressure in the far rooms (and also more negative pressure close to the sucking vent), you will get more outside air mixed. It can be pretty effective in doing what you desire. > > When I open the door to the outside to my utility room with the furnace fan running there can be quite a inrush of fresh (cold) air for this reason. You have an air flow problem in your house that should be looked into. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [October 29, 2015, 6:07pm UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/25 "2015-10-29T18:07:34Z")
> [@ThelmaLou](#): > > I guess this is kind of what I was thinking. Thanks. Only if the house is improperly ducted. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [October 29, 2015, 6:22pm UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/26 "2015-10-29T18:22:04Z")
> [@Habeed](#): > > All the previous posters are wrong. > > The fan circulates air in your house, sucking air in through the intake and exhausting it through the vents. When you open windows, you cause the house air to exchange large air volumes with the outside. > > So with open windows, parts of the house have now exchanged large volumes with the outside of the house. And with the fan running, those cold/hot air regions of the house get mixed together by the forced air. The only this works if you close the bedroom doors and seal them. The fan sucks air from the return air vent or vents in the living space. We are not talking about large volumes of air, velocities or pressure differences. Wit all return air vents open and doors open air will migrate through the doors back to the return air vent. The pressure difference at the return air vent and the living spaces will be in the micron range not enough to cause large volumes of air to be drawn into the house. A better move would be to seal a fan into a window either blowing into the space or outside. ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [October 30, 2015, 4:07am UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/27 "2015-10-30T04:07:23Z")
When I want to exchange inside/outside air quickly (as in changing bedroom temp quickly): Open sliding door (or largest window) Deploy large box (or circular) fan in open door, pointing inward Use ceiling fan on ‘High’ to push air stream from portable fan around the room. The furnace fan does not enter the equation, unless I am using the heat or AC to speed up the temp change ---
**Author:** ![Mudshark](https://avatars.discourse-cdn.com/v4/letter/m/f04885/32.png) [@Mudshark](https://boards.straightdope.com/u/Mudshark)\ **Post date:** [October 30, 2015, 6:29am UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/28 "2015-10-30T06:29:55Z")
> [@Snnipe\_70E](#): > > It does circulate air but it does not bring in air from outside. I thought this was true, unless it was an attic fan. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [October 30, 2015, 12:15pm UTC](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036/29 "2015-10-30T12:15:50Z")
> [@Habeed](#): > > It’s wrong. Then your post is also wrong as we were saying the exact same thing :smack: [Previous page](https://boards.straightdope.com/t/central-heat-air-fan-only-on/736036.md?page=1)