Domestic Hot Water From a Wood Furnace?

[boatboy63]

Before the heating season had started up, I had considered installing a coil in my Buckstove where the heated air blows thru and comes out. I was going to install a tank above it and set up a gravity siphon system, but never had time to do it.

Just wondering if any of you have set up your inside wood furnaces so you can have "free" hot water. I figure if I install something like a 1/2" x 50' roll of copper tubing in the ducting shortly after it comes off the furnace, it should do a very good job of heating water. I would stretch this tubing out some and it would be something like a slinky so it would not reduce the air volume coming from the furnace. I would then do the gravity siphon with it feeding to a storage tank above the furnace. My cold water line would feed to this tank and the hot side of this tank would feed to my electric water heater. If it didn't bring the temps up enough, at least it would act as a pre-heater and supply warmer water to electric tank. I am on a deep well that is about 320' deep and the water during the winter is around 36-38 °F when it comes into the house. This means I am having to heat it nearly 100°F before we can use it. If it would just raise it by 50°F, this should nearly cut my hot water cost in half. I know this is an advantage with an outside wood boiler, but I don't want to have to go out and feed that monster 2-3 times a day during the winter.

 

[Rory]

This being the boiler room and all, I think most of us have boilers, with the majority being indoor gasifier units, and many having a large volume of water to serve as a thermal mass for storing the heat while cranking the boiler and using the stored heat for the house after the fire is out. There is typically a domestic hot water heat exchanger somewhere in the system. In my case, my storage is "unpressurized", simply being a 4 x 4 x 8' insulated rubber lined box with a primary heat exchanger for the heating loop, with a simple solution for DHW. The DHW feed comes in and goes directly to the bottom of the tank, then comes back up through 180' of coiled 3/4" copper. It's hot enough when it exits to require a mixing valve to bring it down to the desired temp. Other folks have more complicated heat exchanger solutions, but I'll let them describe what they have.

 

[Gooserider]

Judging from the description, I'm assuming that boatboy63 is running a hot air furnace, thus no hot water storage to tap into... That said, while it probably CAN be done, it is the kind of project that should be approached with a great deal of caution, as this is the kind of thing that can try to put your house in orbit - and we know how NASA hates home-built competition :coolsmirk:

I'm glad to hear that you are thinking in terms of gravity circulation, and putting the heating coil in the air ducts not the firebox... It would be best if you put it where your heat shouldn't go over 200°F, and definitely make sure that there is NO WAY that you can shut off the flow through the coil, and put a pressure relief valve on the coil so that you don't end up with a bomb...

Gooserider