doublte walled flues

[mm]

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?

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.

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

[dpb]

No, but...

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

That ducting, not 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.

[JRStern]

Huh, makes sense.

Does that mean new high-efficiency has to force air out the exhaust?

J.

[mm]

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

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.

[Lp1331 1p1331]

There is virtually no oil fired equipment in my area, so I all my experience has been on gas units. The main thing about double walled "B" vent is allowable clearance to combustibles. It is generally 1 inch with double and 6 with single. With single wall, a 4 inch pipe would need to have a 16 inch diameter hole in a roof. Larry

[mm]

Yes, after about 8 feet of single wall, winding up and around the furnace to the the metal pipe chimney, and far from combustibles, the chimney is much bigger in diameter and I think it is double wall, but I forget why I think that. Probalby from looking at it from the roof end.

Thanks to everyone.

There is gas 400 feet from my house, but my n'hood of 100 townhouses has no gas. At least I know my neighbors won't burn my house down with a gas explosion, but that's the only benefit.

The electric stove broiler isn't hot enough either afaic.

[Stormin Mormon]

The 80 and 90 percent efficiency furnaces do use a fan to force the flue gasses out. Often called an inducer fan.