Thread: DIY wet back for wood stove

We used to have an Everhot 204 slow combustion stove with water jacket. There is a hot water coil listed on the Everhot site. I'm sorry but I don't remember the size of the copper tubes to the tank. They were 3/4" or 1".
Everhot

Does this help with things?

[ame]http://www.fastonline.org/CD3WD_40/JF/JF_OTHER/SMALL/How%20to%20build%20a%20safe,%20effective%20wood-fired%20hot%20water%20heater....pdf[/ame]


this seems to make it very clear and offer assistance...
http://www.pivotstove.com.au/kb/how-...-and-radiators

We have two galv water pipes (capped) hanging out of the wall directly behind the Wood Combustion Heater so that this can be done here also, as we already use solar heating for the main water heating. (boosted by electricity).

This is of interest to me, as if I can easily convert the already fitted WCH then it would definitely suit. I believe there are also systems to help transfer heat about the house (helpful as we have 10' ceilings here in an old solid farm house).

Watching with interest!

Not directly useful, but I have a factory wetback in my kitchen stove. This heats both hot water and, via a circulating pump, the whole house through pipes in the slab. This wetback comprised a steel (might be cast iron, not sure) box surrounding the fire on all four sides except for the opening for the fire door, with a 1.5" pipe across the top of the fire.

The wetback has connections top and bottom at the back. These are connected to 1" copper pipe risers via shutoff valves, but note that these valves must never be shut while the fire is lit, to avoid explosion. The piping, as pointed out, must rise without any high points, and if just going to a hot water system (in my case directly above the stove) going in top and bottom, with the hot (upper) pipe from the fire going to the bottom of the hot water system.

In my case the water circulating is not directly the hot water system - a special system, it had a coil of 1" pipe to transfer the heat. The rising pipes have tees for the house heating, and a small circulating pump, controlled by a thermal switch that does not allow it to operate until the water returning from the HWS has reached the set hot water temperature. There is also a switch that bypasses the on/off switch if the temperature of water coming from the stove approaches boiling.

John

I have been thinking of doing this as well.
We have a Solar heater and tank on the roof that has pressure relief valves already.
I was thinking of winding a coil of half inch copper tube around the inner flue.
We have about 10 ft between the fire and where it goes through the roof lining. Then T into the Solar pipes with the cold running down the outside of the outer flue into the bottom of the coil. The top of the coil running to the top solar pipe.
Our firebox does not have room for a tank so thought this might work.

Keith

Originally Posted by 123rover50

I have been thinking of doing this as well.
We have a Solar heater and tank on the roof that has pressure relief valves already.
I was thinking of winding a coil of half inch copper tube around the inner flue.
We have about 10 ft between the fire and where it goes through the roof lining. Then T into the Solar pipes with the cold running down the outside of the outer flue into the bottom of the coil. The top of the coil running to the top solar pipe.
Our firebox does not have room for a tank so thought this might work.

Keith

I think it will probably work, but to ensure that thermosyphon action happens you need to ensure there are no high points. All piping should be well insulated. (Not that would round the flue, of course!)

John

How hot do heaters and flus get? Would copper ever get too soft? While water is running through I'm sure it would be fine, but would you allow for any case where the copper is empty? Just curious...

The actual firebox may rarely get hot enough to melt copper, and certainly hot enough to weaken it (but note that copper being a good thermal conductor, provided wall thickness is adequate, heat will rapidly be carried away from the heat source) - obviously not with water in it, but the outside of the inner flue will not get hot enough to worry.

One aspect to allow for is thermal expansion of copper - substantially greater than that of iron or steel.

John

Thanks everyone for your input. That is an excellent article Digger, thanks. I'm under control with the piping from heater to tank. Just the design of the actual heat exchanger in the firebox that I'm still iffy about.

I was going to go with 3/4" heavy wall, hard drawn copper brazed into a ladder type heat exchanger across the back wall of the firebox. This should keep it away from the flue and I can put a plate of steel between it and the front portion of the firebox to prevent damage when loading wood in.
The heat exchanger pipe will leave the rear of the firebox via brass connectors.

I mightn't get around to it for a little while but I will post up build details when I do