Losing Heat Through Bathroom Exhaust Fan

  • Thread starter KodyWallice
  • Start date


May 7, 2021
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  • #1
If there is one thing that I have noticed during this winter, it’s that the bathroom is really cold in the morning. I keep the door closed because I want to concentrate the heat, so that might be the reason. Either way, the whole thing got me thinking.

Can bathroom exhaust vents cause your house to lose heat? I am thinking yes. I did a Google search on this and came across a good article on “Ask The Builder” entitled, “Bathroom Exhaust Fan Leaks Cold Air.” It pretty much covered what I was thinking.

Basically, a bathroom exhaust fan is simply a fan attached to a hose that leads outside. The fan pushes the moist air you create from taking a shower outside, so you don’t rot everything in your bathroom. Some of the fancy fans have lights in them and I am told that the fans vary in quality. I guess they are supposed to have flaps in them too. The flaps stop the cold outside air from leaking directly into your bathroom and house.

I just walked into the bathroom to see if any cold air was leaking through the fan. I put my hand up to the vent and didn’t feel any cold air. Since that felt okay, I pulled down the attic door and went upstairs to see what that looked like. I saw both bathroom vent hoses leading outside. Nothing seemed too out of place.

Now that I am downstairs, I am thinking that I didn’t really do much to see if there was a problem. I mean, I still have to take the vent cover off to see if the vent flap is closing nice and snug. If not, I have to fix that. Then, I would like to cover the exposed vent hoses with insulation. An exposed vent hose in a cold attic can cause the air in the hose to get cold. That air can enter the house if the vent flap isn’t working correctly. Do you see where I am heading with this? I guess it doesn’t help that the boiler is kicking on and off all night, creating a vacuum in the house. Cold air is probably being pulled in through those vents.

I might need to do some more exploration to see if there is some sort of a “makeup air intake port” anywhere around. If not, I probably need to put one in.

Now, I admit, I am no expert at this. Any advice would be appreciated.

COMMENT: I think you might be getting it wrong. it wouldn't be so much that cold air leaks in, than the heat leaking out. all the warmth would be going out of those exhaust vents i think. i have just been thinking a similar thing about the ceiling exhaust fan i have in the kitchen. our house is pretty open plan, so there's nothing really separating the lounge from the kitchen and the hall. which leads to all the bed rooms. so heat from anywhere would most likely be going straight up out of the kitchen exhaust fan.

COMMENT: After a snowstorm the other day, I noticed that there were melted patches directly above my bathroom. I climbed onto a stepladder in the bathroom and could feel some air movement. I put some winter double stick tape on the outside edges of the exhaust vent and stuck a sheet of small bubble wrap over the vent. Hopefully that will help a lot. By the way, I did the same to the “can” light in the living room ceiling, where I suspect there’s also heat loss.

COMMENT: Hi, i also think its your heat escaping rather then cold coming in. As the hot air rises from inside the house, the vent if open will funnel out your accumulated warm air bringing in cold air from floor level usually. You should feel warm air at vent not cold.

COMMENT: Actually, depending on the prevailing winds at your site, cold air may blow in, or warm air may leak out. Many bath vents can be pulled down an inch or so since they have little clips holding them in place. If you are concerned about air flowing through the vent, just put a page of a magazine behind the fan grille and lock it in place. Then remove the page when your are showering and using the fan. It worked for me!

COMMENT: Maybe you need a new replacement part? i didn’t know a exhaust fan could make room lose heat, i thought they brought in heat to ventilate out the steam?

COMMENT: If you leave your exhaust fan run more than it is needed to vent out the steam from a shower or to remove odors from a toilet you will indeed lose heat from your home. The exhaust fan must pull air from somewhere! Leaving the fan running will pull air from your home and if the air is heated your furnace will have to run somewhat longer to replace the heated air you lose!