Back Draft / Condensation

[CNY Joe]

I've been running the Tarm 40 w/o storage since Oct. The Tarm is in the basement and is connected to a triple wall 6" - 20'+ chimney that is fully outside. The flue is comprised of 2 elbows and a 3' straight pipe. Draft is good though I do get a very small amount of leakage (when flue is cold) once in a while around the flue connections.

The Tarm has not been running for over a week and the oil boiler (backup) has been heating the house since I've been on travel. After finally making it home at 1:00 AM, I went to fire up the Tarm only to discover a small pool of water (clear and odorless) underneath it...

After closer inspection, I noticed water droplets around the bottom rear area. Insulation underneath was damp. I run glycol in my system and I checked for leaks - didn't find anything.

I then opened the firebox loading door and noticed a steady cold breeze coming through. The water temp was around 50-60 degrees with 15lbs pressure.

I cleaned the flue, hx and chimney today - no creosote and only a small amount of ash buildup in the flue and chimney.

The only thing I can think of is the cold backdraft kept the firebox/water cooler than room temp thus causing condensation to form on the outside of the boiler and running down through the insulation.... Thoughts? Any ideas on how to resolve or prevent the next time I have to shutdown the Tarm for an extended period of time?

 

[Nofossil]

Sounds like you've got a good theory as well as an interesting problem. The only thing I can think of would be a damper that shuts off 100%. I have a chimney top cast iron damper for my fireplace that does that, but it would be hard to install in your situation.

 

[jebatty]

Can you easily remove the stovepipe that connects to the flue collar on the Tarm and stuff both with some fiberglass insulation? You want to keep air out of the Tarm firebox as well as block off the chimney.