Does Bathroom Fan Vent Duct Need Insulation When In A Heated Space? - Remodeling - DIY Chatroom Home Improvement Forum
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Old 03-05-2014, 10:03 AM   #1
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Does bathroom fan vent duct need insulation when in a heated space?


I'm putting in a new exhaust fan in the lower level and found out the previous fan did not have exhaust vents going to the outside, which I want to correct.

My only choice is to run the vent through the joist bay about 22 feet through our laundry room and out the exterior wall. I want to use rigid 4" ducts for this, but since they will be in a heated area ductwork, do I need to insulate the ducts? I'm in frigid Minnesota. I know this would help a bit with my home heating bill, but wouldn't that cause more condensation in the vent because the duct work would remain colder on the inside?

Is it better to not insulate the duct when going through a heated space to the outside?
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Old 03-05-2014, 10:45 AM   #2
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Quote:
Originally Posted by Studly View Post
I'm putting in a new exhaust fan in the lower level and found out the previous fan did not have exhaust vents going to the outside, which I want to correct.

My only choice is to run the vent through the joist bay about 22 feet through our laundry room and out the exterior wall. I want to use rigid 4" ducts for this, but since they will be in a heated area ductwork, do I need to insulate the ducts? I'm in frigid Minnesota. I know this would help a bit with my home heating bill, but wouldn't that cause more condensation in the vent because the duct work would remain colder on the inside?

Is it better to not insulate the duct when going through a heated space to the outside?
Generally they are only insulated when ran through unheated spaces, such as attics here in Wisconsin.
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Old 03-05-2014, 12:34 PM   #3
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Many cities in Minnesota now require us to insulate the last 3' of exhaust duct prior to exiting the structure. Rather than worry about if the city I am in requires it or not we purchase 10' long duct insulation, cut it in half and insulate the last 5' on every install. I recommend you insulate at least the 3'.
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Old 03-05-2014, 02:50 PM   #4
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I would insulate as far in as possible to keep the cold air from coming in through the duct and escaping into your heated area.

Buy the insulated ducting at the big box stores and pull the flexi line out and insert the rigid ducting.

B
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Old 03-05-2014, 05:34 PM   #5
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Check the exhaust air for dew point temperature and that will answer your question. Worst case possibly - showering. Second worse case - hot steaming tub of water. A steamed mirror is a good indicator of those conditions.

If the pipe is 70F and dew point of the exhaust air is 69 there will be condensation. If the dew point is greater and the pipe temp. less than those numbers, condensation naturally gets worse.
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Old 03-05-2014, 08:55 PM   #6
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Another vote for insulate it all. Cold air from exterior travels to the fan where it is stopped (sort of) by the fan damper. Someone please invent a damper- fan or exterior hood- that is weather-stripped to seal properly (with low resistance). I would buy one over a standard one, every time! Listen-up, you aluminum benders from other lands...

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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 03-05-2014, 09:36 PM   #7
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we insulate the whole run.... ben sr
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Old 04-04-2014, 05:32 PM   #8
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I would think insulating the whole run would be easy enough to do. I ran mine through an uninsulated space and didn't insulate. And do wish I would have. I might have to redo that


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Old 04-04-2014, 11:30 PM   #9
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Installing a ventilation fan in my upstairs bathroom is quickly making it up my to-do list.
Could anyone post links to what they would recommend.
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