Using Woodstove as a Water Pre-heater

[behoof]

Hi,

I did this in the Fall of 2005 and thought I'd share it. I know it's been done before but can't hurt to bring it up again.  I put up a little webpage with my info and pics for you and posted here. Hope it helps someone.

http://www.michigan-horse.org/preheater/

Skipb aka behoof

I live in a small brick ranch on a crawl with LP hot water that costs just too darn much to run.

There are commercial systems out there that would have you cut a hole in your woodburner and install their system. Personally I don't want to put anything inside the firebox or stack for the obvious concern of creosote and the loss of usable burn capacity.

Once I had put some thought into this project I decided to make a system that would not be invasive on my burner and would be simple, fun and efficient.

To begin this project I first cut a piece of .16ga sheet steel the same shape as the side of my woodburner only 1" less all around. Then I took a measurement of 1" less than that on each side, added up the measure of the sides and cut a stick of 1" angle iron that long. I then laid the angle on the .16ga sheet with the open side of the angle facing out (as in pic preheat_4.jpg). I cut and bent the angle so that it forms a sort of dish on top of my .16ga sheet. I used my DC Welder to tack the angle iron in place but you could just as easily drill it and use 1/4" x 1/2" USS bolts and nuts, whichever is the most efficient method for you.

Next I drilled two7/16" OD holes at the bottom/back of the bottom angle iron. This is for the ends of the copper tubing to pass through. I drilled this size so that I could put a piece of neoprene HD tubing through the holes then pass my copper tubing through the neo-tubing, this is to avoid chaffing (as in pic preheat_3 or 4.jpg) of the copper tubing.

Now comes the fun part. you need to pass enough 1/4" copper tubing through one of the neo-tube to give yourself enough to work with when you plumb your pre-heater all together. The next step is one you'll probably want to ask a tolerant friend to help you with, I did it alone and wouldn't ever again LOL. What you do now is carefully start making coils of your 1/4" copper tubing inside the "bowl" of your angle iron. Just keep going round and round and filling as much of the 1" angle iron "bowl" as you can without having it pop up over the top edge of your angle. It can get a bit tedious but it can be done.

After I made 75 feet of copper tubing coils I ran the other end out of the second neo-tube and cut off the excess. Next I went to my local ACE Hardware and get 20# of Plaster of Paris. I mixed of the plaster and poured it into my angle iron "bowl" then took an extra piece of angle iron and leveled off the top. For saftey against my coils popping up out of my Plaster of Paris I put a piece of 3/4" plywood on top of it and weighed it down and let it sit for a couple of days.

For mounting your pre-heater coil to your stove I guess you could just drill holes and use washers and stove cement but I chose to weld 1 1/2" USS bolts directly to the stove and that way when I was working with my pre-heater it was just hanging on the side of the stove, I didn't have to support it.

Now that I have my pre-heater mounted on my stove I go to the water heater and remove the drain valve and fitting on the bottom of the water heater (mine is a Rheem 50gal with 3/4" pipe) I installed a pipe nipple and Tee and reinstalled the drain valve on the Tee. On the side of the Tee I installed my TACO Pump (you can get one off of Ebay for $80 or less) with the direction of flow toward the Stove Mounted Pre-Heater. On the outlet side of the TACO Pump I install a copper reducer to get me down to 1/4" copper tubing. (Note: you could just as easily use 1/2" hard copper tubing to plumb from your 1/4" soft copper Pre-Heater to your water heater if you have to run any distance, just be sure to insulate it)

I now go up on top of the water heater to the outlet copper pipe which is also 3/4" and install a 3/4" Tee in the 3/4" pipe between the Relief Valve and the hot water tank. Then I sweat on a 90' ell and the necessary brass to get me down to 1/4" copper pipe. ( Note: Again remember that you could just as easily use 1/2" copper hard tubing)

I now run 1/4"soft copper tubing wrapped with insulation from my copper tubing inlet and outlet on my woodburner pre-heater to the TACO Pump and to the line hot water inlet fitting at the top.

Next I mount my thermostat ( I used an AC Type ) approximatly 1 1/2' from the back of my woodburner, that way as the stove heats up it will signal the TACO Pump to kick in as soon as the thermostat reaches your upper setting.

Now you need to refill and bleed your lines and that's just about it.

I've added the pictures below to show basically how this is all done and a picture of the basic parts needed to accomplish building your own woodburning water pre-heater.

NO MORE HOT WATER BILL IN THE WOODBURNING SEASON !!!

(see notes at bottom of page)

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Pre-heater mounted on woodstove copper not plumbed yet

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Preheat mounted not plumbed

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Preheat prior to mounting

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Preheat showing Plater of Paris bed for copper tubing

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Preheat 2nd view before install

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Preheat Some of parts

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Preheat installing on woodstove

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Preheat pump I got on Ebay

My Parts List:

1. 50' Soft Copper Tubing
   
20. lbs. Plaster of Paris
    
    

.16ga Sheet Steel

1. "x 1" Angle Iron ( length according to your stove size)
   
6. 5/16" x 1 1/2" USS bolts
   
12. 5/16" USS nuts
    
1. TACO or other brand circulating pump
   
1. Air Conditioning Type home thermostat
   
1. 3/4" Pipe Tee
   
2. 3/4" Pipe Nipple
   
1. 3/4" Threaded to copper tube adapter
   
1. 3/4" Tee
   
1. 1/2" copper street Ell
   
   

Necessary brass fittings to reduce down to 1/4" soft copper

Misc. fittings to adapt to needed unions.

Of course your fittings and other misc. items will vary with stove and your added ideas to this project.

Note: I haven't had any issues with overheating and I ran my woodburner at full tilt for four hours with the pump unplugged. It showed no signs of having any issues.

One thing that might be a good idea and I may very well do this myself just as a saftey precaution is install a temp sensor on my water heater and wire in a high temp shut down. Like I said though, I'm sure I won't need it but just to be on the safe side and besides I love doing this energy saving stuff!

Another thing you could do depending on your needs is add a second unit as the pre-heater for your main water heater. I think this would mate very well using solar, bio or other forms of energy to preheat your water.

Skipb  aka behoof

[willib]

neat idea !

nice work!

[behoof]

Thank you willib, it was a fun project and boy can it make the HOT water <smile>

Skip  aka behoof

[willib]

yeah i'll bet it can.

you could move it outside in summer?

[strider3700]

Beautiful

I wonder if you've thought about a way to mount it that doesn't involve welding or drilling to the stove.   i've got a brand new woodstove now  and i'm sure the wife won't like the concept of me welding on it

Maybe I should look into a gravity held system  sitting on the top...

[behoof]

strider3700,

I considered making clamps to hold it on as temporary to see if it was worth the trouble (fun) of doing this project. I though of using long treaded rods across the top and bottom to hold it in place while I tested my idea but I decided that since my welded on bolts would not even be visible and should I decide to remove this pre-heater I could simply grind them off and repaint, there would be no reason, in my case not to just attach the pre-heater as describe. I'm glad I did, it works super! And the only energy I'm using right now is a trickle to power the pump from my inverter.

A gravity system could work nicely but opted for my design because you really can't even tell that it's there unless I tell you to take a look at it! I considered a gravity system, an invasion of the burner box with coils and other apperatus but decided I didn't want to do anything to change my burners combustion chamber... it works great so why mess with it? I find that the pre-heater has no effect on the side it's attached to, no build of creosote or heat/coolspot issues at all. I just get nice evenly heated copper tubing (thank you plaster of paris).

I'm planning to run solar water heat in the summer and am working on that system now for installation this Spring.

Thanks for the note,

Skip  aka behoof

[behoof]

willibur,

No, I don't think I'd go to that much trouble. I'm setting up a solar system for installation in the Spring to handle the warm weather hot water needs..

Thanks,

Skip aka behoof

[georgeodjungle]

every thing looks good

but for the long term, cooper and galvanized shouldn't touch.

[behoof]

georgeodjungle,

Thanks and I agree... dissimilar metals and all that... I had a Marina for years and learned all sorts of interesting facts regarding anodes and such.

Thanks for the reminder,

Skip  aka behoof

[elvin1949]

Hi Skip

 I like it [simple and all that stuff].

Not much to break.

later

Elvin

[behoof]

Elvin,

Thanks, I agree and it was a lot of fun to do... if you like this kind of stuff that is LOL

Be Well,

Skipb  aka behoof

[Shadow]

Very neat looking set-up! I'll be trying this for sure.Is there any safety measures if the circulating pump dosent kick in?I might be inclined to cover the two copper pipes coming out of the wood stove with a second pipe or something in case one of them ever burst.Or does the heated water automatically flow into the water heater?

[behoof]

Shadow,

I put a shutoff valve on both copper tubes just at the in and outlet near the pre-heater, IN CASE. I suppose you could cover them with something but I haven't had a lick of trouble with this setup at all, no problems. And the way mine is plumbed my main shut off valve still has control over the entire system.

As I mentioned in my article on the webpage link I put in the article and in the article itself, I ran my burner for quite a long time at full tilt (over 4 hours actually) with the pump disconnected and I had absolutely no problems develope.

As for automatic flow, I suppose that gravity/heat transfer would move the water somewhat but not to any appreciable amount. I've heard about some very inexpensive pulse pumps out there but I opted for the TACO pump because they get used with hydronic heat a lot and they are modulized for easy replacement of parts without having to remove the pump assy from the system.

Good luck and have fun,

Skipb aka behoof

[RP]

"I put a shutoff valve on both copper tubes just at the in and outlet near the pre-heater, IN CASE."

DANGER WILL ROBINSON!

Never ever ever turn off both valves at the same time when the stove is lit or there is ANY possibility someone might light it.  Steam is a very nasty animal and with both valves shut, the pressures will rise to hundreds and even thousands of pounds before something lets go in very dramatic and unfortunate manner.

Sorry for the rant but I had to say something.

[behoof]

russp,

I do understand your point fully and I'm sure there is a possibility should both valves be closed at the same time. If the temp were to rise to the point of boiling or very near to it. I put the valves one on each side of the tube (in and out of the pre-heater) in case of a leak in front or in back of the pre-heater. The valves in my set up were also for disconnecting the stove to take it out for repair or as I say for a leak on the in or outbound side.

You bring up a very good point and certainly one that merits attention. So, as I concur with russp that were both shutoff valves closed at once and you got your burner hot enough to boil the water in the tubing I'm sure it would be possible to burst the tubing inside the plaster of paris bed that it's in or possibly split the copper and get a heck of a leak when you opened your valves back up. Although as I've mentioned previously I ran my burner at max - full-tilt for over four hours with no issues. In the time I was running the burner at full the valves were open. I may just run a test to see if anything will happen because I'd hate to see anyone hurt or property damaged.

Not to belabor the point though, even though it gives me great hot water (130 to 150 degrees at the hotest so far) I've had no indication of the water going beyond this area. I guess if someone has a Super Stove of some sort or perhaps were to bring their copper tubing in contact with the stove wall and not have it embedded in the plater of paris fully it could probably get unevenly hot or chaff from the hot/cold movent of the metals?

If I get the chance to run a valve closed test I'll post my results or if anyone else has any thoughts on this would love to hear.

Thanks russp,

Skipb  aka behoof

[elvin1949]

Skip

 If it was me, I would try to install a pressure relif valve between the heater coils and one of the valve's. Just in case [better safe than sorry].

later

Elvin

[behoof]

elvin1949,

Yes, actually after answering that last post I came to the same conclusion. I was sitting there looking at my drawings and noticed how I had moved the hot water heater relief valve up a bit to accomodate the tube to the burner and it struck me.

Simple, safe and common sense.

I guess GREAT MINDS really do think alike LOL

Thanks for the input.

Regards,

Skipb  aka behoof

[ghurd]

Nice!

I don't know much about it, but I believe gravity feed would work if the copper were 1/2"~3/4" and the hot water not forced to flow down (no coils). Maybe just a bunch of verticle legs?

Might be worth scrounging some 3/4" copper for an experiment? It would take a lot of 'T's.

I like the plaster of paris.

This thing has no pump. The outside is a water jacket so there are no coils or lines. It is the only heat for the water. The storage tank is a standard 40 gal gas water heater.  It supplied all the hot water for 10 people earlier, 6~7 people now. Remarkedly stable water temperature in the storage tank.  But the safty relief valve DOES open every year of so.

It is purpose built, factory made, coal fed.  Uses "about a coffee can of coal a day, sometimes 2."  LOL

Not the most pleasant room in the summer.

But no pump!

G-

[elvin1949]

ghurd

 wish i had one of those BUT they are hard to find in the deep south [louisiana].

 I could fire it with homemade charcoal [hardwood].

Lot's of oak and beech here.

later

elvin

[ghurd]

They are not cheap, but they do ship them all over. Probably made in eastern PA, central OH, or IN.  There is probably a distributor in KY (Mumfordville?), most southern I can think of.  Some go west too.  I could check around if someone really wants one.

G-

[behoof]

ghurd and elvin1949,

I don't know if you are familiar with Lehman's Catalog?

Anyway, it's a really fun catalog, kinda Omish in nature...

They also have a website at   www.Lehmans.com

and a toll free at 1-877-438-5346  

don't know where you're all at but I bet some of you could really HELP their phone bill a bit LOL

Anyway, it's a fun catalog full of NON-electricity stuff...

I remember seeing a water heater like ghurds quite a while back and I think it was in Lehman's... not really sure though...

Be Well,

Skipb   aka behoof

[ghurd]

That's not mine.  That one is in an Amish house.  Who else would have a family of 10? (12 actually, but 2 moved out before that water heater was installed). Dinner is something to see, especially Friday with the married kids&spouces, grandchildren, and friends.

The trouble with Lehman's is their prices, but the quality of the products they handle is good. Some people use their catalog like a referance book, then find another place that sells the item.  

They do have obsolete item made, like grates and castings from about every known wood / coal stove. 2 thumbs up for that.

The guy who owns that water heater is a grandfather, his Mom still uses his grandmothers woodburner cook stove, which his grandmother purchased used when she was young... So that puppy was made in the 1800's.  The grate or shaker or something inside burned out a couple years ago.  Lehman's had it IN STOCK !!!

[behoof]

ghurd,

Yeah, that is cool... in stock for an 1800's OEM type part, go figure will you? Amazing ....

Yeah, Lehman's is pricey but it is just such a fun catalog that I just thought to share it because I know I leave a copy of it sitting in my living room and when ever anyone comes by they ALWAYS grab it and start browsing.  

Talk to you,

Skipb aka behoof

[behoof]

elvin1949,  

After thinking about it, I DO have a reliev valve in-line... I moved the existing relief valve up a few inches to accodate the input line from the burner so it is still actively protecting the entire system.

On the other hand, were I to shut both valves at once and light the burner, the loop of copper in the plaster of paris would be unprotected.

Just thought to mention this...

Later,

behoof

[elvin1949]

That was the part i was thinking of.

 later

Elvin

[haselbury]

Hi SkipB,

Thanks a lot for adding this - I'm trying to build two of these in the next couple of weeks.

Question: Are you still running this as described? Have you had any issue with pump reliability pumping through the 75 feet of 1/4" (8mm) copper tube?

I just ask because I read that microbore pipe runs should not be longer than roughly 14m (46 feet) because of resistance of the small bore pipe against the pumped water flow, so wondered if I should use 10mm tube instead. If you've been running this regularly for some time then I guess it hasn't caused you any pump failure problems? Also, how long is the run from your tank to the start of the 1/4" coil? I think you ran that in 1/4" as well, from the pump?

Also, what method did you use for bending the pipe in such a long coil? did you just hand bend it around a reel, or use some form of pipe bender tool?

Many thanks

Jonathan