Do I need a make up air vent


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Old 02-24-19, 12:37 PM
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Do I need a make up air vent

We live in a 20 year old home. Average construction but seems pretty air tight. The forced air propane furnace is in the vented attic. No gas burning appliances inside the home. We have an electric clothes dryer and bathroom ventilation fans all with ducts to the outside. Should we have some sort of make up air vent for the house?
 
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Old 02-24-19, 01:30 PM
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Nope. Why do you ask??????????????????
 
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Old 02-24-19, 01:56 PM
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We are new to this house and bought a new electric clothes dryer that does not seem to dry well. Wondered if it could be because the house was too air tight. Thus impacting the dryer efficiency. Also baths seem to stay humid even with vents running.
Must just be because of the ambient humidity. It is around 55% in the winter. We are used to a much drier climate.
 
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Old 02-24-19, 11:26 PM
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If you can narrow down your location, maybe your nearest big city we will have a better idea as to your outside weather. 55% RH means different things at different temperatures.

Doubtful you have a "too tight" house builders just don't go to that extreme unless someone is paying the extra. The threshold when tested is around 1/3 air exchange per hour of natural leakage.

When the bath fans are running they need a source of air from the house, usually under the door. They also need a "delayed off" power switch to keep them running for 20 or 30 minutes after the shower.

Bud
 
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Old 02-25-19, 04:39 AM
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We live in Ocean Isle Beach NC. It is about 30 miles north of Myrtle Beach SC. We are 1 mile from the ocean. I have a few Acurite devices around the home monitoring the humidity inside the home, outside, and in my crawl space. The house stays around 55% most of the time during the winter. Outdoors varies obviously a lot day to day and depending on outdoor temp. Summer is much higher outdoors. Right now it is 44 degrees outside and 39% humidity inside and outside, low for us.

Dryer vent to outdoors is long, about 20 feet, but has good flow.

I do not have a real reason to believe the house is too tight other than the dryer taking longer to dry than I expected. Admittedly I am comparing to our old house in Colorado in the hills at about 8300 feet. Different dryer, different house, and much lower humidity.

Thought maybe this house might be tighter than I expected and possibly the dryer was limited by lack of make up air.
 
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Old 02-25-19, 05:09 AM
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When a home is experiencing the 1/3 air change per hour that means that same volume of outside air is entering and needs to be heated. Heating air at 44 and 39% RH results in 70 air at 21% RH. The rest of the moisture to get up to 39% is coming from the people inside and their activities and yours sounds normal.

During very cold weather condensation on the inside of windows (without the curtains pulled) is a real world indication of less air exchange. Better windows will be less affected, single pane (not yours) will show up at warmer temps. Usually the condensation rating of good windows is well below freezing.

Back to your dryer, I don't know. Make sure there is no lint accumulation and check for a good airflow. That long of a run could be limiting airflow somewhat.

Easy to test by cracking a window ". It should show up on your humidity readings. Here is an RH calculator that helps track inside and outside humidity.
Temperature, Dewpoint, and Relative Humidity Calculator

Bud
 
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Old 02-25-19, 05:21 AM
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Could be something as simple as a kink in the flexible duct behind the dryer. But yeah... completely different dryer, completely different climate.
 
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Old 02-25-19, 06:30 AM
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Ok, thanks for all the info. I will quit worrying about it. I'll try cracking a window next time we run the dryer and see if it makes a difference.
 
 

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