Making a external DHW Coil

Hello first off this is one of the most interesting message board.. Very Informative.
My question is this, I have a Keystoker Stoker 90K. It has been in service for seven heating seasons. We love it. After having it I have installed two others in relatives homes.
After reading through this message board I am now thinking of heating my domestic water with it.. So seeing that I need a storage tank, I put a ad on craigslist for a used water heater. Within 6 hours I have a 80 gallon AO Smith electric water heater. Now for a coil. Is it possible to make a coil out of 3/4" fin tube (that is used for baseboard heat)? What I thought about doing is making several vertical rows of fin tube connected via a header on top and bottom. I would make the "coil" the size of the side of the coal stove. Then connect it in a traditional way to the storage tank like discussed throughout the site.

Last night I checked the temperatures of the side of the stove (via infrared), mind you I was not really calling for a lot of heat (fire) and I had temperatures around 340 f

Thoughts?

Thanks in advance..

most people that try adding a coil for hot water end up being disapointed with the results.
you would be better off looking for a deal on a used coal boiler,
with #2 heating oil at $2.23/gal there is a good chance you will find one.

here is a link to boilers for sale
Furnaces, HVAC, Plumbing Supplies-4Sale

I beg to differ, I put a single loop coil in my stove at the begining of last season and couldn't be happier with it. In the spring and fall it will preheat the water so the NG heater doesn't run as much and in the dead of winter it will keep the NG tank from firing at all. last year I had my coil tank tied straight into my HW lines and it supplied all of our hot water needs. This year I piped it into the supply of our NG tank, so in essence I have 80 gal.of HW vs. 40. There also some other members on here that have installed a coil and are happy also. Bug512, I don't know if anyone else has tried it this way, but if you do, let us know how it works out. You may get the water up to temp. but I think the recovery will be extremely long. With my single loop coil over the firebed it still take anywhere from 5-8 hrs to recover. Keep in mind I'm using the thermosiphon method with no pumps. Good Luck.

Jeff

well it is good to hear that it can be done and it works well.

here is a link to some that didn't work so well
Less hotwater than expected from Koil

It seems to me that the fin tube should be horizontal so the fins are aligned for best air circulation.

With the fins holding the copper tubes away from the hot surface, then conduction will be poor. Why not a flat copper tank the full size of the stove surface pressed up against it? Far better conduction. Circulation will also be much better. Enclose with insulation the outer surface.

Richard

Thanks for all the responses.

syncmaster wrote:most people that try adding a coil for hot water end up being disapointed with the results.
you would be better off looking for a deal on a used coal boiler,
with #2 heating oil at $2.23/gal there is a good chance you will find one.

here is a link to boilers for sale
Furnaces, HVAC, Plumbing Supplies-4Sale

Well that is a good idea but I have a direct vent keystoker ... so no chimney ..

ceccil wrote:Bug512, I don't know if anyone else has tried it this way, but if you do, let us know how it works out. You may get the water up to temp. but I think the recovery will be extremely long. With my single loop coil over the firebed it still take anywhere from 5-8 hrs to recover. Keep in mind I'm using the thermosiphon method with no pumps. Good Luck.

Jeff

As far as recovery time. It is just my wife and I in the house. We get up for work around 4 AM in the morning and return around 5 PM. We both take showers in the morning also. So... It has some time to make up especially with 80 gallons of storage.

franco b wrote:It seems to me that the fin tube should be horizontal so the fins are aligned for best air circulation.

With the fins holding the copper tubes away from the hot surface, then conduction will be poor. Why not a flat copper tank the full size of the stove surface pressed up against it? Far better conduction. Circulation will also be much better. Enclose with insulation the outer surface.

Richard

Yes that is a good point. I had thought about having two pieces of 3' fin tube against the hottest side of the stove and possibly making a cover around them to retain the heat around the tubes.

Well I thank you all again for your comments.

Gene

If you are buying the fined tubing, I'd try something else, but if you have the finned tubing already, I'd go ahead and experiment.

There is a similar external water heater for sale on ebay from time to time. I do believe the recovery time will be very slow, but like you explained you have lots of time for the recovery of water temp.

If you do use finned tubing, make sure you don't end up having the fins transfer heat into the room. You do need air flow around the fins to recover the heat from the stove's side, but you want to capture this heat, not 'share' it with the room the stove is in.

A few years back, a forum member made a heat recovery system that used an airconditioning condenser resting on the top of his stove, and he was successful with cutting his hot water electric bill, so it can be done.

Best of luck, Greg L

syncmaster wrote:well it is good to hear that it can be done and it works well.

here is a link to some that didn't work so well
Less hotwater than expected from Koil

If i may add. It does work, its just after all my reading about the coils people have installed and heating there water i assumed with the size of the coil i installed i would be getting more hotwater than i am. As Ceccil has added to the thread listed above the stove has really not ran hard yet this year as temps arnt that cold. I do have a rather small house to heat so the coal-trol is satisfied rather quickly.

I did get my first electric bill and was shocked to see about a $100 decrease from the month before. i would have to give that credit to the hotwater heater not running as much. We do use allot of hot water as i am starting to realize. Running the washing machine with warm water does some damage.

At the rate im going now i will pay for the coil install this year.

Well it looks like I am going forward with the project. Again I acquired a 80 gallon AO Smith electric water heater for free. I tested it with water and 50# pressure this morning and it does not leak.

The next step is to finalize drawings. I have a expansion tank already along with other copper hardware.
I think I am gong to go with two or three, 3 foot sections of fin tube. They will connect via a 3/4" header. I still think I will orient them in a vertical fashion since I will first try to circulate the water via a thermosiphon.

LsFarm wrote:There is a similar external water heater for sale on ebay from time to time.

I as actually looking at one of those before deciding on an internal coil. I was worried about how much hot water it would actually make and recovery times vs. the cost. Seemed a bit much not knowing how well it was going to work.

Jeff

There are units out there that do that, OR heres an article. Do your research.

http://www.motherearthnews.com/Do-It-Yo ... Stove.aspx

But just be careful and have the safety devices installed properly.
http://www.woodheat.org/dhw/dhw.htm


I saw some air/water coils on Ebay, nice tidy little box you mount on the side or top of your stove.

Well I started the external hot water coil today. Here are some pictures of the coil I made. More posts and pictures to follow in the next couple of weeks.

Coil on side of stove:

Bottom Side of Coil with drain:

Top Side of Coil with T&P valve:

Four magnets with pipe hangers to keep coil in place:

Nice job, looks like it might work, you may have to put a cover of them to keep the heat in.
Thermosyphon may not work as well as you expect, you may want to have the plumbing in for a small circ. pump.

I will be useing a small bronze pump.

Looks Great!! Four magnets with pipe hangers to keep coil in place, Love that Idea!!!