[steppinthrax]

So here's the deal. Over the weekend I just did a new install for a Nutone 80CFM bathroom vent fan. The bathroom is a small full bath in the master. When I mean small it's pretty much sink next to toilet next to tub.

The bathroom never had a ventilation fan ever. We've been having "surface mold" issues along the top of the ceiling. This had been occurring because when taking a shower the mirror/windows would fog up and water would essentially condense on the walls.

So the fan I put in has a very short run (1 foot) of 4" pipe that pretty much shoots to the roof. I did a quick test where I took a long shower with hot water and noticed it does a very good job of removing the "fog/steam" in the bathroom and the mirror barely gets foggy.

However, you see a film of water on the door casing and on some areas of the walls.

I guess my thought is that it's doing as good as it could do?

 

[keithhe]

Not sure your square footage and cubic footage, but your description leads me to believe perhaps 35 square foot, or 280 cubic feet (assumes 8' ceiling). That means your fan is moving a room change of air every 3-1/2 minutes. A bit more CFM would be better, or leave fan on longer.

Most people turn off fan right after leaving a shower when there is still a lot of moist air in the room. Get in habit of leaving it on for 5 minutes or so after.

 

[steppinthrax]

Not sure your square footage and cubic footage, but your description leads me to believe perhaps 35 square foot, or 280 cubic feet (assumes 8' ceiling). That means your fan is moving a room change of air every 3-1/2 minutes. A bit more CFM would be better, or leave fan on longer.

Most people turn off fan right after leaving a shower when there is still a lot of moist air in the room. Get in habit of leaving it on for 5 minutes or so after.

I figured 80CFM should be sufficient. Yeah I leave it on for a few mins afterwards to clear out the room.

Other thing I was thinking is putting a vent in the door. I notice when I had my foot on the floor (next to the door bottom). I could feel cold air moving into the bathroom.

 

[keithhe]

A very tight door could add to the problem, but a vent is pretty fugly? Can you cut bottom to allow a little more free air flow?

 

[RegeSullivan]

My rule of thumb is 1.5 times the size of the vent pipe for make up air. So if you have a 4" vent pipe connected to your fan... 4 X 3.14 = 12.6. 12.6 X 1.5 = 18.9 sq in. It seems like a lot but on a 24" door 1" clearance at the bottom gives you more than enough. If you have an open heat register in the room that would also count toward area for makeup air.

A timer that would allow you to leave the fan on for up to 30 minutes might be helpful. You could start with 30 minutes and keep cutting back on the time until you figure out how long it need to be on the dry out the bathroom after a shower.

 

[steppinthrax]

My rule of thumb is 1.5 times the size of the vent pipe for make up air. So if you have a 4" vent pipe connected to your fan... 4 X 3.14 = 12.6. 12.6 X 1.5 = 18.9 sq in. It seems like a lot but on a 24" door 1" clearance at the bottom gives you more than enough. If you have an open heat register in the room that would also count toward area for makeup air.

A timer that would allow you to leave the fan on for up to 30 minutes might be helpful. You could start with 30 minutes and keep cutting back on the time until you figure out how long it need to be on the dry out the bathroom after a shower.

Thanks, I remember that there is a floor register in the room so essentially it's sucking air from there as well.

I guess my question is if I put a bigger CFM fan in there will I essentially ELIMINATE any water from condensing on the walls. Also would this even be advisable.

 

[Bud9051]

A longer running fan will do a better job than a bigger fan. The fan is always dealing with a room full of moist air and once off, the remaining moisture is there to condense on the walls. If the fan continues to run, it gradually takes the moisture level down with each air exchange. They make on/off switches with an adjustable delayed off just for this purpose.

When you say your fan shoots to the roof, I assume you mean through the roof .

Bud

 

[jimn]

80 Cfm is fine. You should run probably for 25 minutes after you shut the shower off. I have hot water baseboard heat (almost as a good as a good steam system) so not much air circulation between rooms. I have a push button (electronic timer) timer on mine set for 20 minutes. Assuming a 5 minute or so shower , it cleans the air well and drops the humidity down.

 

[TheEplumber]

Moved to HVAC

 

[Bob Sanders]

Do you have forced air heating/cooling in your home?

Make sure the CFM out is more than the CFM coming from your heating vent. Otherwise you will form a positive pressure in the bathroom while in heat/cool mode and any odors will end up in the hallway instead of up and out by the exhaust fan.

 

[beenthere]

Put it on a timer, and leave it run for 10 to 15 minutes after your done showering.