Chimney Reheat Coil???

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Status
Not open for further replies.

mattd860

Member
Feb 21, 2011
40
Eastern, CT
Does anyone make a water coil that can be inserted into a 6" diameter chimney flu? I would like to pre-heat the boiler return water by running the water through a chimney coil of some type. Google searches have yielded no results.

If nothing exists, can I wrap some flexible copper pipe around the chimney flu piping and then insulate it?? I have 1.25" Black Iron piping returning to the boiler. I should be able to 'tee' off to a 'Y' and then reduce down to two strands of 5/8" flexible copper pipe. Then I can wrap the two strands of copper pipe around the chimney a bunch of times and then reconnect to the boiler return line.

Any thoughts???
 
Put a pressure relief valve at the entrance to the coil and one at the exit. Make sure there are no valves or ways to isolate the prvs from the coil. There are unexpected failure modes for these, but it seldom happens. Only takes once.

Coil inside/around the pipe = lots of cleaning time to remove the creosote that collects and insulates the heat transfer surfaces.
 
I suspect you'll have more problems than succeses with the preheat setup. Have you calculated what your flow rate would be through your proposed 5/8" lines? Do that once and see how fast the water would be moving through your coils. And do a quick check on how much volume you'd actually have in the coils. Assuming it worked (big assumption) I suspect you'd be adding a very small amount of heat to your return water overall. Just my guess, however.
 
stee6043 said:
Assuming it worked (big assumption) I suspect you'd be adding a very small amount of heat to your return water overall.

The other side of the coin is, would you be pulling too much heat out of your stack gas to prevent creosote condensation?
 
I would say its not a good idea unless you can install the necessary controls to prevent creosote/condensation as mentioned above. Any of the potential gains I think are outweighed by the potential problems of flue gas condensation. Now, if you have a NG boiler and flue that can handle condensing, thats a separate issue and you could post over on the "Its a Gas" forum and see what you get.
 
Status
Not open for further replies.