# Do I need to insulate my duct?



## brendanstl (Jan 29, 2010)

Thought id ask before I wasted the money. None of my duct is insulated in my basement - crawlspace, I have a vent punched out down there but there is condensation dripping off of the duct like crazy. Our house was built in the early thirties on top of limestone footing with clay block foundation, I've done my best at sealing all penetration but still get a lot of hot and cold air down there. My problem upstairs is during the last week with temperatures in the upper 90s and humidity levels to match, the air conditioner has not shut off once trying to keep the house at 70 and all it will cool to is 72-74 degrees, I would guess we are at about 70 percent humidity in the house. The walls are insulated and wrapped with tyvek at the exterior along with having good replacement windows that are insulated and installed properly. I've had the air conditioner checked for leaks and everything is good along with it being properly sized for our home. Do you guys think that insulating the duct would take care of these issues?


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## SLSTech (Sep 13, 2008)

Yes & No as you listed oh so many issues

Condensation - yes & that might also help some with the high humidity as you do have a ton of moisture being dumped on the basement / crawl floor (raising the thermostat setting might help with that also)

Your AC running almost non stop - that is what should be happening, thus it is right sized. Have you checked the condesate pan to make sure it is draining properly (and out to daylight away from your foundation)

The vent in the basement / crawlspace - is that a sealed crawl & insulated basement? Plastic on the crawl floor? Are they seperated from each other?

Besides insulating, you need to pop a dehumidifer or two in the house / basement to help get those levels down & get a duct test done to get any leaks sealed up & while you are at it, a blower door test would probably be a good idea to find out where the air leaking in is coming from


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## beenthere (Mar 5, 2009)

If you only have a supply in the basement/crawlspace. Then your putting your house into a negative pressure. And pulling in fresh air through any and all cracks that it can come through.

If the basement/crawlspace is sealed, add a return. if its not sealed. Then close off that supply, and insulate the ducts.


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## brendanstl (Jan 29, 2010)

beenthere said:


> If you only have a supply in the basement/crawlspace. Then your putting your house into a negative pressure. And pulling in fresh air through any and all cracks that it can come through.
> 
> If the basement/crawlspace is sealed, add a return. if its not sealed. Then close off that supply, and insulate the ducts.


There is only a supply in the basement, can you tell me how that works that the supply causes air to be sucked in, I would figure that it would force air out if it wasn't sealed off good.


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## beenthere (Mar 5, 2009)

brendanstl said:


> There is only a supply in the basement, can you tell me how that works that the supply causes air to be sucked in, I would figure that it would force air out if it wasn't sealed off good.



It causes air to be sucked into the main area of the home because the air that is blown into t\he basement has to replaced somehow.

Its your main living area that goers into a negative pressure. The air from there is the air that is being blown into the basement.


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## Dr Heat (Dec 25, 2008)

If you have 70% RH at 72 degrees your system is not properly sized. 

Now I did not say the condenser was the wrong size. 

I would check the fan curve on your blower it is my suspicion you need to slow it down. 

Have a pro check the size of the evaporator coil If the evap is not properly matched you will not dehumidify properly where I live we always oversize the evap to add additional de-humidification.

As for sealing and insulating basement ducts if the basement is a sealed usable space and the ducts are of standard construction and properly installed. insulating them may cause problems.


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