Hercules

My dad called me asking about flu pipes. He bought a Hitzer fireplace insert for his existing fireplace because of the internal blower to spread heat better. He's been looking into stainless steel flu pipes for the installation, when he had a thought. Why does he need one when he's been burning in the existing fireplace that this insert is going into for 33 years? I think he may have a point. The fireplace this insert is going into already has a teracotta flu liner. I'm calling it teracotta because that's what it looks like, but, it may be some other material that just looks like teracotta. He told me it has an 11" diameter. It was installed when the house was built back in the 60's. He's never had a problem burning in that fireplace and it has vented perfectly. So, does anyone know anything about this and can give some advice? Thanks for the info!

Hillcountry

When I was a kid we ran the flu pipe for our wood stove all the way up and capped it at the top even though we had the same terracotta stuff you mention. It helped with the draft and with cleaning. Code may have rules about this also, but I am not sure.

hamilton71801

When I put my insert in, my chimney was straight up with no lining whatsoever. I put a 10" flexible pipe on the stove to make sure it drafted properly and then wrapped the back of the stove with insulation and it works great. It's been this way for 10 years and never had any problems.

DuaneWKKC

If the flu is LARGER than required by the new stove, you will probably get more condensation in the flu, increasing creosote (sp?) buildup. Newer stoves are much more efficient at getting the heat out of the stove and into the house, which should mean cooler flu gasses and LESS flu gasses. In old systems, excess air was always being pulled through the stove, resulting in heat loss. Newer stoves are better at controlling the air flow to maximize heat extraction efficiency (some better than others). The more efficient the stove the more correct flu sizing matters. A higher efficiency stove will have LOWER exhaust gas temps AND VOLUME, meaning if the flu is too large you have a MUCH better chance at getting into a cold stacking situation.

So in a word, yes it does matter and if it were me, I would run an insulated liner up the flu if larger than required for the stove.

DuaneW.

EDIT: just reread your post, realized that he had been burning in an open fireplace. The same principle still applies, open fireplace = large volumes of hot gasses going up chimney = not much creosote buildup. Again, a good efficient stove does not operate the same way, but has restricted air flow.

ALSO, I would use OUTSIDE air. It is amazing the difference it can make in the moisture inside your house and in how well the stove operates under varying conditions.

Hercules

Thanks for the info! I got to talk with him again today. I asked him if he found a flu requirement in the installation manual. After some digging, he finally noticed a section that he missed that said the flu had to be 8" diameter. Thanks again!