On Thu, 05 Nov 2009 20:06:03 -0600, dpb wrote:

mm wrote:
I'm reading another thread about furnaces, the long thread where the
house won't heat up "furnace blowing all the heat up the chimney" and
someone wrote that flues are double-walled. Is that always the case?

No, but...

Beginning w/ 80% efficiency units they will be; older convective exhaust
not.

Well that's the difference. I have older convective exhaust.

Maybe his furnace is gas and mine is oil? Because my flue is single-
walled. Is that bad? As long as it doesn't cool off so much that the
chimney doesn't draw well, any heat lost from the non-insulated flue
would heat the basement.

That ducting, not flue.

When I get a new oil furnace (no gas supply) should the new one have a
double-walled flue?

It will if it's high-efficiency as noted above.

Have to be or else they'll condense inside since exit gases are so much
cooler in higher efficiency units.

Okay, I get it. It also makes me feel better about last weeks
experience in Home Depot. I was in a hurry so I asked a clerk where
flue pipe was, and he said something about double wall and said they
didn't have any. Later I asked another clerk and he walked me right
to what I needed. The first clerk wasn't young but he was living in
the present. The second guy was the same age and found it for me, but
the first had a reason for his mistake.

Thahks a lot.