I have a portable AC unit connected to a window. Will running my furnace fan help circulate the cold air? Or is it pulling in hot air outside?

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    I use to do that all the time. You may have to close the outside air make up for the AC months. Not knowing your system closing the make up is just a guess.
    – Gil
    Jun 26 '21 at 1:56
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    Most portable A/C are terribly undersized for doing the whole house, so that part may disappoint. If there is makeup air being pulled in, then it will be. If there is not, it won't be.
    – Ecnerwal
    Jun 26 '21 at 2:14
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    A 1-hose portable A/C is definitely going to pull in outside air! Hot humid outside air. It will draw in the same amount of air that it ejects out the one hose. If it has 2 hoses it won't have that problem. Jun 26 '21 at 5:33
  • Did not know about the single hose issue! The machine i bought was $699 and has a single hose. Every other one I've ever bought was under $300 and had two. Insane heat wave happening here in Alberta, so I'll have to deal! Also sold out everywhere in Alberta.
    – Shinobii
    Jun 27 '21 at 5:17
  • I think a regular fan will be more effective for moving air. Jun 30 '21 at 16:18

I have used the furnace to circulate even swamp cooler air not really cold but cooler and it made the home a bit more comfortable.

If you have a make up air intake damper close it almost all the way down you only need a tiny amount of make up air when the fan is on full time.

Yes your single hose is pushing really hot air out but some air will be drawn in to the home one short term suggestion I make to homeowners is to slightly open the access to your crawl space. Opening the crawl space pulls cooler air in from under the home as long as the air going out is hotter than the air coming in the home will be cooled.

Even air movement alone helps us to be cooler so the air handler running distributes the air evenly through the home and moving air also helps.

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    There may be some psychology to consider also. Rather than use your furnace to circulate a very limited amount of cold air, perhaps if you sealed the air conditioned room as best you can, and cooled only that room, and combined that with creating air flow as suggested in this Answer in all the other rooms, you would end up with a situation where all the other rooms FEEL a little cooler, and one room feels nice and chilly, and the net effect will be better comfort everywhere.
    – jay613
    Jun 30 '21 at 16:13

Some furnaces only circulate air and do not draw in fresh air. If you have one of those (only circulating) it may feel like it is pulling in hot air simply because the A/C is not capable of cooling your whole house in addition to the HVAC ducts themselves and through them the attic/basement/walls or wherever else they go. In fact, if the ductwork runs through the attic who knows, it may pull more heat in that way than is removed by the A/C! To improve your chances slightly you can make sure doors are open, or closed, to the rooms you want cooled or not cooled respectively, and don't forget to keep cleaning or replacing your furnace filters while you are running the fan even if you are not heating. You may find that just leaving interior doors open circulates the air well enough, and conserves more of the coolness for your living spaces.

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    It depends if the home has makeup air. if just running the fan will draw in outside air if the home has a make up air intake. With increased sealing over the last 30 years it is quite common to have an outside air intake or makeup air. I put dampers on the systems I install as the air is drawn from the attic space more often because that air is not musky compared to crawl space air.
    – Ed Beal
    Jun 30 '21 at 15:52
  • Thanks for the comment and new answer. I've clarified my answer pertains only to systems without makeup air.
    – jay613
    Jun 30 '21 at 16:08

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