Furnace Vent

[pnarron]

I putting a new furnace (Thermal Zone 80% 75,000 btu) in the attic and I noticed a rubber seal around the draft inducer coller; is that just to help protect it during shipping or for a better seal? I would think that it would melt, but the vent pipe will go over it, without it it is a little lose. The only dumb question is one that is not asked, howerver this does come close.

[Brian A. MacNeish]

Originally Posted by pnarron

I putting a new furnace (Thermal Zone 80% 75,000 btu) in the attic and I noticed a rubber seal around the draft inducer coller; is that just to help protect it during shipping or for a better seal? I would think that it would melt, but the vent pipe will go over it, without it it is a little lose. The only dumb question is one that is not asked, howerver this does come close.

That "rubber" material is the colour of hi-temp silicone. It may be there to provide a better seal against potential flue gas leakage. If it's a mid-efficiency furnace in the 80-85% range flue gases will be lower (300-350*F) due to more heat being extracted from them.

[rsmith24]

If all else fails read the Manuel. Whats up with all the Spackle?

[pnarron]

The manual does not say anything about other than to pre-drill holes. the other stuff is mastic to seal off the joints.

[Tim Spargo]

I agree with Brian, it looks like hi temp material. Pre-Drill holes for vent take off/ connection.. good idea. They probably say that (pre drill) as the little metal shavings fall down into the inducer fan from the self-tappers, or the self tappers distort the high temp gasket.

[pnarron]

Thanks for the help!

[Doug Edwards]

Originally Posted by rsmith24

If all else fails read the Manuel. Whats up with all the Spackle?

That is "hard cast" or mastic, to seal all the joints, cracks, seams etc. It is now mandatory in my neck of the country. One report I just recently read, they (whoever, "they" are) determined many home lose somewhere close to 20% of their heating / cooling in the attic where seams, joints and connections are old, loose or just disconnected. Most flex duct is held on with plastic zip ties at the collars. Results in air leaks, and especially condensation.

[Brian A. MacNeish]

Originally Posted by dedwards

That is "hard cast" or mastic*, to seal all the joints, cracks, seams etc. It is now mandatory in my neck of the country.
Someone in your government is reading and thinking, especially if it's required for residential installations.

One report I just recently read, they (whoever, "they" are) determined many home lose somewhere close to 20% of their heating / cooling in the attic where seams, joints and connections are old, loose or just disconnected. Most flex duct is held on with plastic zip ties at the collars. Results in air leaks, and especially condensation.

"They" may be DOE/Oak Ridge National Labs, NAHB or Lawrence-Berkley Labs. Reports of residential duct air leakage rates were reported in Home Energy magazine as far back as the 1980's/early 90's. They claimed that the research found that 20-40% of the air flowing through the HVAC air handler (fan) did not come from or get to the rooms it was designed for!!

* The mastic is more formally called high velocity duct sealer. A great but cheap product near the vicosity of acrylic caulking that can be applied to clean duct joints with a 2-3" wide paint brush. A better technique would have the duct joints wrapped in a fiberglass tape prior to sealer aplication.

[pnarron]

I used metal tape and then applied the mastic over that. Thanks again for everones help!

[Brian A. MacNeish]

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Originally Posted by pnarron

I used metal tape and then applied the mastic over that. Thanks again for everones help!

In the long run, will the sealer adhere to the foil tape with the expansion/contraction of the ducts?

[Doug Edwards]

That is exactly what is required here. The code tape has to be applied, then the mastic. I often find where someone has applied just plain metal foil tape but it did not adhere. For those who don't know the difference; code tape will have printing on the surface while the regular foil tape will not. If anyone uses the non code tape, it will fail a county inspection. So far I have never witnessed any problems with expansion of fiberglass duct board or issues with the tape and mastic combination failing.