Condensation from HVAC vents

[lildex93]

First let me thank everyone for the great reading content on this page it has helped me tremendously. Going into my second year with a new Heat N Glow Northstar XC wood stove. We recently had a few days / nights that have been relatively cold and burning has taken place quite a bit with great success. I have been moving cool air throughout my ranch style home with 2 box fans, one on each end with fireplace near the center of the home. Last night while an overnight burn was going I got dripped on by condensation out of the HVAC vent above my bed. After researching more this morning there is a cold draft coming out of the duct work.

My thoughts- The box fan in my room blowing cool air towards the fireplace is creating a draft through the ductwork causing the cold attic air in the ductwork to become warm and condensate. When looking this morning the ductwork is sealed around the drywall and the cold air/condensation is strictly coming from inside the ductwork, not from around. I did just recently change the vent in my air returns to high flow vents because during the summer months my bedroom was staying warmer than the rest of the home. Is is too much to ask to sleep comfortably?

Has this happened to anyone else and is there a solution?

 

[TradEddie]

I'd imagine that a cold draft out of supply ductwork is normal (I get those drafts in my home too, but I've never seen condensation). If your ceiling boots or attic ducts are not well insulated, then you could get condensation if the source of the air was humid. You don't see this when the central air is running because it'll dry out each time the thermostat kicks in.
I'd look at the ceiling boot and try add insulation, I used that sticky rubber foil-backed stuff, initially on the inside of the boot, but eventually I went up into my disgusting attic crawl space and added it to the "outside" too. I also taped the end of the duct wrap better than the installers had done. I did this to reduce heat loss, and try reduce the drafts due to convection of cooled air.
TE

 

[EbS-P]

We have pull down attic stairs. This summer I insulated the ladder with a zippered hatch. The door is sealed with weather stripping. Last week while going up I noticed condensation on the inside of the hatch. This week nothing. My explanation, the first cold week the house was still fairly humid. Now it has dried out to the point that it’s not condensing.
I’m skeptical any amount of insulation would prevent condensation in the ducts when not using the hvac system .

if the issue persists it must be addressed. Condensation in ducts is a recipe for Bad things. Could be as simple as a dehumidifier or using a a programmableT star to run the system some. Or both it it could be a convective loop established itself and hit air goes in one vent and cold air out the other. Taping some plastic wrap might help stop the draft and allow to monitor for condensation.
Couple thoughts.
Evan

 

[TradEddie]

If you are truly not using your HVAC at all, try closing all your supply register dampers. A convective loop is exactly what I figured causes my draft, with some help from stack effect, and I will say that improving the duct and boot insulation reduced but did not eliminate the draft.

TE

 

[lildex93]

We have pull down attic stairs. This summer I insulated the ladder with a zippered hatch. The door is sealed with weather stripping. Last week while going up I noticed condensation on the inside of the hatch. This week nothing. My explanation, the first cold week the house was still fairly humid. Now it has dried out to the point that it’s not condensing.
I’m skeptical any amount of insulation would prevent condensation in the ducts when not using the hvac system .

if the issue persists it must be addressed. Condensation in ducts is a recipe for Bad things. Could be as simple as a dehumidifier or using a a programmableT star to run the system some. Or both it it could be a convective loop established itself and hit air goes in one vent and cold air out the other. Taping some plastic wrap might help stop the draft and allow to monitor for condensation.
Couple thoughts.
Evan

That is a good thought. House drying out now that we are hitting the cooler drier months. May try running the vent fans tonight for a few hours once the fire gets going. Maybe this will blow any of the more warm moist air out of the duct work.

 

[Tron]

I would agree. I have sensors on two of my ceiling-mounted HVAC registers, and they cool down significantly at night (when the HVAC is off). After all, it's a more or less direct path to the attic.
I run the fans a few minutes every hour to filtrate the air, and that's enough to bring the ducts back to "house temperature".
So if the attic ductwork cools down, which it inevitably will when not being used for heating or air circulation, and the air in the house is warm and moist, some of that will find its way into the duct and could condense. Nothing you can do about that, really. Even with better insulation, the ducts are still likely to get colder than the dew point in the house.

 

[Sailrmike]

First let me thank everyone for the great reading content on this page it has helped me tremendously. Going into my second year with a new Heat N Glow Northstar XC wood stove. We recently had a few days / nights that have been relatively cold and burning has taken place quite a bit with great success. I have been moving cool air throughout my ranch style home with 2 box fans, one on each end with fireplace near the center of the home. Last night while an overnight burn was going I got dripped on by condensation out of the HVAC vent above my bed. After researching more this morning there is a cold draft coming out of the duct work.

My thoughts- The box fan in my room blowing cool air towards the fireplace is creating a draft through the ductwork causing the cold attic air in the ductwork to become warm and condensate. When looking this morning the ductwork is sealed around the drywall and the cold air/condensation is strictly coming from inside the ductwork, not from around. I did just recently change the vent in my air returns to high flow vents because during the summer months my bedroom was staying warmer than the rest of the home. Is is too much to ask to sleep comfortably?

Has this happened to anyone else and is there a solution?

I installed these this year:



They kinda remind me of those microwave plate covers lol but much better looking than the foam boards I used last year. A few winters ago when it got bitterly cold here, i got a stain in the sheetrock next to a vent.