Hot Water Coil

[10moreyears]

Anybody using a hot water coil with a woodstove? If so, what are your experiences? I can see a possible problem with EPA-certified stoves by influencing heat distribution and altering secondary burn.

The reason I am interested in this is for a source of hot water in the winter for an off-grid house. Gasification boilers seem to use quite a bit of power for fans and pumps, whereas a thermosiphon hot water coil and tank in the second floor or attic would require no electricity (and be less expensive).

Hot water coils are options on most wood cookstoves, but don't seem to be an option on any heating stoves. There is a company (Therma-coil) that offers kits to install hot water coils. I assume that this would be limited to steel stoves; cast iron and soapstone being too thick.

Any thoughts & experiences would be welcome.

 

[log-on]

We are just installing a passive coil loop in a cook stove.There will also be solar loop. This is for an off the grid Yurt. We found the same as you, they say a coil will effect an EPA stoves burn temp messing it up so they only recomend installing coils in non-compliant ( exempt from EPA ) appliances. We did read about some people installing a coil on the top or side of wood heating stoves with minor success. Make sure you use lot's of saftey blow out valves , there is plenty of pictures on the web of systems that exploded when the owner forgot to open a valve before lighting a fire. Good Luck.

 

[webbie]

My preference has always been to find a stove with a heavily radiant rear plate and install an external finned coil (S shaped, with two or three back and forths) between the stove and a heat shield. It may not heat as well, but the danger of overheat is much less.

 

[10moreyears]

Make sure you use lot's of saftey blow out valves , there is plenty of pictures on the web of systems that exploded when the owner forgot to open a valve before lighting a fire. Good Luck.

Yes, I have seen those references as well. I don't think it is a good thing to put a shut-off valve in thermosiphon systems; forgetting to open it seems like a fairly substantial risk.

My preference has always been to find a stove with a heavily radiant rear plate and install an external finned coil (S shaped, with two or three back and forths) between the stove and a heat shield. It may not heat as well, but the danger of overheat is much less.

Yes, on further reflection, it seems that putting a hot water coil in the combustion chamber of a wood stove used as the main source of heat in a house is probably a bad idea. It might cause problems with secondary combustion and is likely to overheat unless hot water is monitored carefully and used regularly. A cookstove used only for short periods of time each day is probably a better idea.

What we need is for some company to incorporate heat pipes like are used with evacuated tube solar panels into a wood stove. That way the heat would be regulated at about 180 degrees and steam explosions wouldn't be an issue. Unfortunately, I expect that the number of people interested in such a setup would be too low to justify the engineering costs.

 

[log-on]

I used to have a coil like that on the side of my Fisher , it worked great until the storage tank packed it in. It was just a pre-heat tank so I gave up, This install is in my Daughters place.
Yes the blow outs occurred when people would shut down for the summer and then forget to open the valves in the fall. The shut off valves are a necessary evil. Apparently you should not leave the water in the loop over the summer as it will sweat and could rust out your stoves firebox. Another reason is the hot water will continue to circulate and you’ll be radiating heat from the coil which may be unwanted BTU’s when it’s 90 in the shade outside. We are installing unions at the coil and will shut the coil off from the tank , then drain it. This seems fool proof. Our tank does not have electric back up, it’s 100% solar and wood so it will be a seasonal switch over. Anybody out there think we should install a anti scalding valve on the hot water output?? They show this in a lot of the diagrams.

 

[10moreyears]

Yes the blow outs occurred when people would shut down for the summer and then forget to open the valves in the fall. The shut off valves are a necessary evil. Apparently you should not leave the water in the loop over the summer as it will sweat and could rust out your stoves firebox. Another reason is the hot water will continue to circulate and you’ll be radiating heat from the coil which may be unwanted BTU’s when it’s 90 in the shade outside. We are installing unions at the coil and will shut the coil off from the tank , then drain it. This seems fool proof. Our tank does not have electric back up, it’s 100% solar and wood so it will be a seasonal switch over. Anybody out there think we should install a anti scalding valve on the hot water output??

A check-valve would stop the circulation problem; of course, the check-valve could freeze shut, so... it would seem that your solution of shutting off the flow and then draining the lines is probably the way to go. I would recommend a good anti-scald tempering valve on any water heater that could exceed ~120-140 degrees.

 

[keyman923]

I'm thinking a stainless coil sitting on the top or side of my secondary stove in the near future like in this article.

http://www.motherearthnews.com/Green-Homes/1984-01-01/A-Woodstove-Water-Heating-Attachment.aspx

With 1 of these pumps that I could run just a few hours a day or every other day.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130206330607

I really don't want to drill my stove to run it inside the firebox. If I could get the water up to 90-100 degree's it would be a big help in the winter. I started on my solar batch heater last week and hope to have it up and running sometime this week if I can just figure out if I want a horizontal or vertical set up but I'm leaning toward a vertical set up.