Cold air coming through the ducts?

[woodjack]

I use my oil, forced air system as a back-up to my wood heat, but the ducts are cold air channels to my living space from the basement/furnance room. I cover the vents with towels, but then they're closed if the heat kicks on. Do any of you guys have this problem - and a solution?

 

[LLigetfa]

There is probably a make-up air duct feeding fresh outside air into it. If you don't have a OAK for you stove, I suggest you add one if available to reduce demand for make-up air. You could redirect the make-up air to where the stove is so it can get warmed. You could find where warm air is leaking out of your house to reduce the amount of make-up air needed.

I redirected the make-up air to our upstairs bedroom. Since cold air doesn't like going up, less air comes in. We like the bedroom to be cooler so that helps. We also like fresh air in the bedroom so we can get fresh air without opening the window.

 

[begreen]

If this is an older system and no make up air, it is likely just a cold basement. Insulating the ducts or better yet the basement, sill plate and rim joists will reduce this cold air significantly.

 

[brooktrout]

ALOT of woodburners with forced hot air systems for backup with non-heated basements have this dilemma. I do, and it's been discussed before. Covering the ducts is no good, for reasons you stated, and puts alot of stress on the furnace if it does kick on. I wish there were a product to slip under the vents that would open and shut when the furnace cycles. I know there are motorized ones you can install, but they're cost prohibitive. Some kind of light weight flexible flap that would flex open with the air pressure......

 

[LLigetfa]

Still, it comes down to simple physics. Cold air is heavy and doesn't want to leave the basement. It doesn't go up unless there is a pressure imbalance causing it. Turn a paper coffee cup over and stick it in water. The water doesn't fill the cup. Poke a hole in the bottom of it and the air leaks out, filling it with water.

Fix all the places warm air leaks out of the house and less cold air has to rush in to replace it. Even if there isn't a make-up air duct in the basement, the basement probably leaks in outside air. Sealing up the cold air infiltration is not the solution. Providing make-up air to the stove is.

 

[woodjack]

The ducts run from the furnace room which is freezing because the furnace is usually not on.

Sometimes I turn on the furnace for a boost to get my house a few degrees warmer, but then I have to uncover all the vents - and remember to cover them again when the furnace turns off.

I thought that maybe there was a vent product that I was unaware of that provided a simple solution to this problem.

 

[woodjack]

Still, it comes down to simple physics. Cold air is heavy and doesn't want to leave the basement. It doesn't go up unless there is a pressure imbalance causing it. Turn a paper coffee cup over and stick it in water. The water doesn't fill the cup. Poke a hole in the bottom of it and the air leaks out, filling it with water.

Fix all the places warm air leaks out of the house and less cold air has to rush in to replace it. Even if there isn't a make-up air duct in the basement, the basement probably leaks in outside air. Sealing up the cold air infiltration is not the solution. Providing make-up air to the stove is.

Yes, my house leaks air like a sieve, as much as I tried to seal leaks. Regardless, open vents are like having open windows.

 

[Crabbypatty]

woodjack, i would seal the ducts in the basement with a duct seal product, not foil tape. if all of the joints and seams in the duct are sealed, then the cool air in your basement is not going to infiltrate the duct and find it's way to your registers. is the duct insulated? this just makes it a tougher job to seal if it is. then you can use the hvac system to your advantage and put your t-stat on fan and let it circulate the warm air around the home. you can get a gallon of ductseal at a local HVAC supply house for less than $20.

 

[LLigetfa]

Range hoods, dryer vents, HRV vents, etc. use a flapper style check valve to prevent reverse flow of air. You could make your own with metal louvers from window blinds.

 

[woodjack]

woodjack, i would seal the ducts in the basement with a duct seal product, not foil tape. if all of the joints and seams in the duct are sealed, then the cool air in your basement is not going to infiltrate the duct and find it's way to your registers. is the duct insulated? this just makes it a tougher job to seal if it is. then you can use the hvac system to your advantage and put your t-stat on fan and let it circulate the warm air around the home. you can get a gallon of ductseal at a local HVAC supply house for less than $20.

Okay - that's my weekend project. Although I'm not sure it will help much I'll give it a try.

Range hoods, dryer vents, HRV vents, etc. use a flapper style check valve to prevent reverse flow of air. You could make your own with metal louvers from window blinds.

Great idea. Have you done it? I could imagine that product in every Home Depot and Lowes around the country.

 

[Crabbypatty]

LLigetfa, i think, is refering to a simple gravity operated back draft damper. to install something like that on each register would be expensive and labor intensive.

 

[Crabbypatty]

if you are going to seal, please use a mastic style sealant you brush on or caulk on and put it on thick so it does it's job. duct tape and foil tape are used incorrectly all of the time, and i see it falling off all of the time. if it doesn't solve the problem completely, at least you are increasing the effiency of the duct system when you are running the oil furnace. Also take a look at the furnace it's self and make sure there aren't any major leaks, especially where the duct attaches to it.

 

[LLigetfa]

LLigetfa, i think, is refering to a simple gravity operated back draft damper. to install something like that on each register would be expensive and labor intensive.

That of course depends on what the OP has for cold returns and where they are (wall versus floor).

I still think stopping the cold air at the return register is the wrong thing to do. A leaky house needs make-up air. Reduce the amount of warm air leaving and you reduce the volume of make-up air needed. Pipe some make-up air directly over to the stove and it will not suck it up from the basement. The basement will be warmer too if cold air isn't passing through it.

 

[LLigetfa]

Crabbypatty makes a good point. Go over your entire duct system and seal every joint, not with cloth duct tape but with mastic or foil tape. Unconditioned basements don't usually have cold returns in them so the cold air is probably leaking INTO the cold return ducts. Cold air, like water, takes the path of least resistance. Analyze the path with a smoke pencil if it isn't obvious.

The OP has to explain how the cold air is getting into the basement.

 

[Crabbypatty]

LLigetfa, i think, is refering to a simple gravity operated back draft damper. to install something like that on each register would be expensive and labor intensive.

That of course depends on what the OP has for cold returns and where they are (wall versus floor).

I still think stopping the cold air at the return register is the wrong thing to do.

A leaky house needs make-up air. Reduce the amount of warm air leaving and you reduce the volume of make-up air needed. Pipe some make-up air directly over to the stove and it will not suck it up from the basement. The basement will be warmer too if cold air isn't passing through it.

i agree, it's similar to a resturaunt that doesn't turn the make up air unit on, or doesn't have one, but wants to know why the dining room is so drafty. i think he will benifit from some duct sealing, unless he has a outside air intake on the duct system with no damper on it. a OAK or duct will help as well, providing fresh air to the stove directly. i would start with the ductsealing, and if done properly, he should be pleased with the results.

 

[woodjack]

if you are going to seal, please use a mastic style sealant you brush on or caulk on and put it on thick so it does it's job. duct tape and foil tape are used incorrectly all of the time, and i see it falling off all of the time. if it doesn't solve the problem completely, at least you are increasing the effiency of the duct system when you are running the oil furnace. Also take a look at the furnace it's self and make sure there aren't any major leaks, especially where the duct attaches to it.

I could have used that advice a year ago. I spent many hours fastidiously putting foil tape on all the joints. Half of it is off already.
I was thinking of using expandable foam. Instead of letting it sit on the duct and bubble up, I'm going to brush it on so it collapses into a glue. That stuff is crazy strong so I think it will work. I got a couple of tubes of duct sealant if all else fails.

And I'll continue the never ending quest to seal my house from air infiltration.
Thanks guys.

 

[LLigetfa]

And I'll continue the never ending quest to seal my house from air infiltration.
Thanks guys.

That is a nooby mistake. A house and it's occupants need air. Warm air leaving the house is the real culprit. It's just not as noticable because you don't feel the draft. Cold air comes in to replace the warm air that leaves. Less warm air leaving means less cold air coming in.

Warm, moist air leaking out through your building envelope will cause that moisture to condense inside that envelope. It is said that one single leaky electrical outlet can condense upto SIX GALLONS of water in your wall.

 

[Crabbypatty]

i would rather you use ductseal for the ducts.........rather than greatstuff foam. ductseal does the job very well, and save the greatstuff for your foundation and other air leaks

 

[KateC]

I've been battling the same problem and it's pretty confounding. We wrapped all the ducts completely with Reflectix insulation---basically bubble-wrap covered with foil on both sides. Used it also to cover the basement door to outside and wrap the hot water tank---it's helped alot but I was still getting a very cold draft from the duct in the stove room as the blower was sucking that cold air right across the floor. That one I closed and covered with a towel since we don't need any supp. heat in that room but the others stay open. I have a small fan on the floor in the bedroom doorway blowing toward the stove and that seems to help the stove not try to suck air from elsewhere. It's made a big difference. We've also been working on finding and sealing leaks--caulking windows and draft-stopping doors, etc. Little by little we're getting there.

 

[begreen]

if you are going to seal, please use a mastic style sealant you brush on or caulk on and put it on thick so it does it's job. duct tape and foil tape are used incorrectly all of the time, and i see it falling off all of the time. if it doesn't solve the problem completely, at least you are increasing the effiency of the duct system when you are running the oil furnace. Also take a look at the furnace it's self and make sure there aren't any major leaks, especially where the duct attaches to it.

I could have used that advice a year ago. I spent many hours fastidiously putting foil tape on all the joints. Half of it is off already.
I was thinking of using expandable foam. Instead of letting it sit on the duct and bubble up, I'm going to brush it on so it collapses into a glue. That stuff is crazy strong so I think it will work. I got a couple of tubes of duct sealant if all else fails.

And I'll continue the never ending quest to seal my house from air infiltration.
Thanks guys.

Usually a good metal tape will stick and hold on to just about anything, but the surface must be clean first. A lot of ductwork has a layer of dust on it that filters down from the floor above. Clean the ducts well before applying mastic or tape.

 

[woodjack]

As instructed, I scrubbed the ducts with alcohol before I applied the metal duct tape. I don't know if it's the expansion/contraction of the ducts or the surface itself, but that tape would not stay on strong and tight in certain spots.

 

[Crabbypatty]

woodjack, adhesive foil tape is not designed to adhere to metal. it has an acrylic adhesive and it is primarily made to seal the vapor barrier on duct insulation. the only tape product that i use to seal sheet metal duct joints is made by hardcast and is labeled 1402. it is a foil tape but it has a modifed buytl sealant on the back. My cost per 3" x 100' roll is $28.00. it is expensive but it works well. Thats why i reccomended a paint brush applied mastic duct sealant. it gets in the joints and dries hard and seals the duct very well for about $20 a gallon. as far as insulation on the ducts, it's performance is directly related to wether the ducts are sealed properly. Reflectix is a great product, but to maximize the r value you have to install spacers so you have an air gap all around the duct. even FSK fiberglass blanket needs to be installed correctly to achieve maximum r value. too tight it is compressed at the corners and you lose the r value too loose and it hangs off the duct and sags.

 

[begreen]

Nashua 322/324 is designed for foil and fiberboard insulation, but Nashua 327 is specified for metal (butyl backed). I did a friend's system about 20 years ago. Although I don't remember which Nashua type I used, the tape on it is holding well and looks like new.

FWIW, I was lazy with our system and used 324a on metal and the insulation jacket. So far, after 3 years, it is still holding well in all places. .

(broken link removed to http://www.covalenceadhesives.com/Data/Transient/Docs/Products/Info/Choosing_the_Correct_Foil_Tape.pdf)
(broken link removed to http://www.covalenceadhesives.com/SearchProductsDetails.aspx?ID=81)

 

[Crabbypatty]

i am not familiar with nashua's products, but if it has a buytl backing, and it's designed to seal air ducts, i assume it is fine. i just didn't want to see woodjack waste his time with some foil tape he picked up at harbor freight for .50 a roll. it also has to do with the installation as well. most tapes are pressure sensitive and will adhere much better if rubbed with a squedgee.

 

[woodjack]

Crabbypatty, I took your advice and used a duct sealant instead of the expanding foam. I had some caulk style duct sealant so I used what I already had.

What about the air intake ducts and registers? Inside my home, I keep them covered because they spew a constant stream of cold air. I keep them closed all the time, even when I turn on the furnace.

And how important is it to seal leaks in the air intake ducts in the furnace room? I figure they are getting plenty of air through the spaces at duct connections.