A few air duct questions

[mike van]

Not really boiler, but so many knowledgeable people on this forum, I thought i'd ask here - Our twins are going to move into our old farmhouse soon, old hot air system put in in 1962 [furnace replaced in the early 90's] Bare metal 2x12 hot air ducts. Could I get any better results from insulating them, or going to round insulated ones? That furnace seems to run & run with barley warm air coming out the vents, full dirt floor cellar. Much of the heat from that furnace seems to go up the chimney, after firing it up, less than a minute you can't touch the pipe. When I was a kid we had a huge old wood furnace there, one 4x4 ft cast grate in the downstairs hall, you couldn't stand on it when it was going. Dry wet mittens in minutes though - Any thoughts?

 

[STIHLY DAN]

Your ductwork is absolutely your problem. I will send a pic of the installation requirements of a 60,000 btu unit in just a moment.

 

[STIHLY DAN]

Here it is.

 

[woodsmaster]

Would probably help to seal the ducts. There is a sealant you put on with a brush, but I can't think what it is called. Next best way to seal is with foil tape. After sealing it then insulate it. If you really want to improve efficiency install a high efficiency furnace, but sealing and insulating is a good start that wont break the bank.

 

[DoubleB]

Your ductwork is absolutely your problem.

@mike van , I am pretty sure this means your ducts are too small. You can insulate small ducts and still have your current problems. You can install bigger/more ducts, and solve the problem potentially without insulating them.

At least that's my bet based on your post.

 

[woodsmaster]

What size is the main trunk ? I assume the 2 x 12 is the register opening in the floor ?

 

[mike van]

I'll get some measurements today -

 

[mike van]

A little more info - The furnace is marked Thermopride, 126000 btu The hot side plenum is 22 x 22 and 24" tall. The return side is 22 x 16 & 24" tall. Hope these pics help, not an easy place to get good ones. return is on the right side in the first pic.

There are three of the large ducts that are 8x12 for heat, several 6" round come off of them. House is huge, one part 26x26 full 2 story w/ full attic, an addition 16 x 25 2 story, and another about 12 x 20.

 

[woodsmaster]

I'm no hvac expert, but id guess that sealing and insulating would help a lot.

 

[STIHLY DAN]

The ducts are large enough. Air sealing every joint will help alot, insulating them will help more.

 

[Yankee]

Looks like mine, except I have redone the foundation and basement. How long since the heat exchanger has been cleaned? These are a good solid furnace, but do get plugged up in a couple of years.

 

[mike van]

The furnace was last cleaned by a pro 4 years ago- But, since then only 275 gal of oil through ti. Most days / nights the big All Nighter stove did the job. I can look into it & see how she looks though.

 

[DaveH]

"There is a sealant you put on with a brush, but I can't think what it is called. "


Mastic duct sealant. Cheap, not too messy, and effective. I used it with mesh drywall tape. Much more effective and permanent than foil tape, and probably cheaper.

 

[peakbagger]

You mentioned "twins" which I assume are children?. If possible get pro in a clean the ducts. Its amazing how much dust and junk can build up in the ducts over the years especially with an older home. Oil furnaces have to run higher exhaust temps then gas furnaces but even with oil there are low efficiency contractor specials and higher efficiency units.

 

[mike van]

Soon to be 26 - I bet there is some duct in those ducts too -