Hot Cast Iron + Cold Water...

[Peter B.]

A number of years ago, I wrapped multiple coils of 3/8" copper tube around the cast iron firebox of an old parlor stove. I then tried some goofy (but fun) experiments with a thermosiphon system. I finally realized I'd never gain a thing unless I pumped the hot water away from the (already) heated area.

But fortunately, I stopped to consider what might happen when cold water was pumped back to the copper coils surrounding the cast firebox... and I never put the idea to the test.

The stove is still used daily and has some antique value, so I wouldn't want to crack the firebox in an 'idle' experiment.

Any opinions from anyone with boiler experience what I'd be likely to expect?

(I'd consider trying the thermosiphon again with a 35 or 55 gallon barrel 'storage' tank, but I'm afraid the floor near the stove won't take that much more weight.)

Thanks for any replies...

Peter B.

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[Eric Johnson]

I'm not real clear on what you're asking, though I have heated with a Round Oak in central Wisconsin through some pretty wicked cold snaps.

Bear in mind that any hydronic heating system needs, at minimum:

Pressure relief valve
Expansion tank
Pressure/Temp gauge
Some sort of reservoir
A radiator or some other radiant device to dissipate the heat

As a practical matter, a Round Oak is so inefficient that if you're at all serious about producing hot water by burning wood, you should find a used boiler and play around with that.

 

[Peter B.]

I'm not real clear on what you're asking, though I have heated with a Round Oak in central Wisconsin through some pretty wicked cold snaps.

<snip>

As a practical matter, a Round Oak is so inefficient that if you're at all serious about producing hot water by burning wood, you should find a used boiler and play around with that.

Thanks, Eric...

To restate the question: Is there a) a very good chance the cast firebox would crack if cold return water was circulated through the copper coils, b) a moderate chance, c) a minimal chance, d) no chance at all.

Only in the event of 'c)' or 'd)' would I want to even try the experiment.

--

I'm aware of the Round Oak's overall limitations, but it's all I've got to fool around with at the moment.

Peter B.

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[Eric Johnson]

A couple of weeks ago when my boiler overheated, I opened up the valves to my gravity-feed overheat protection system, which consists of two cast iron radiators in the attic above my barn. I have to keep the radiators empty because I don't have antifreeze in my system, and the rads would freeze up otherwise. Anyway, that was 220+ water going into 30-degree cast iron. No problems. I realize that you're going the other way (hot cast iron/cold water), but I don't see why the results would be any different.

How cold is the water and why is it cold? If you fire up the stove with water in the piping, it should all heat up uniformly at the same time. If you circulate the water (or it thermsiphons), the "cold" water entering the piping will still be pretty warm. I'm guessing room temp or higher.

Bottom line, I'd say the chances are about zero that the temp differential would crack the cast iron.

Good luck & safety first.

 

[Peter B.]

How cold is the water and why is it cold? If you fire up the stove with water in the piping, it should all heat up uniformly at the same time. If you circulate the water (or it thermsiphons), the "cold" water entering the piping will still be pretty warm. I'm guessing room temp or higher.

Eric:

If I were to give a pumped system a try, I would want to run the heated water to another room (which might initially be unheated). I assume the return line might be cold... say as low as 40* F. The attached pic shows the copper coil wrap. The lowest coil (empty of water) is only warm to the touch. The top coil is extremely hot.

Bottom line, I’d say the chances are about zero that the temp differential would crack the cast iron.

Obviously, I can't ask for a guarantee, but based on the above, would you still make the same conclusion?

Thanks Again.

Peter B.

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[Eric Johnson]

Based solely upon my experience with the cast iron radiators and the fact that I doubt your return water will be anywhere near as cold as 40 degrees, I come to the same conclusion.

Why don't you try heating up a cast iron kettle on the stove and drop into the snow or a cold pot of water and see what happens? And bear in mind that the return water--no matter how cold it is, isn't going to be contacting the cast iron directly. The copper tubing it's flowing into is going to be pretty damn hot to begin with, so the cast iron will never see much temp differential.

 

[Peter B.]

Okay... I'm resting a little easier with the idea.

Can anyone recommend a good (reasonably inexpensive) low (or adjustable) capacity hot water pump? I'd probably only be running one or (at most) two baseboard heaters... that is, if one worked successfully to begin with.

Peter B.

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[Eric Johnson]

You can pick up a Taco 007 at Home Depot for about $70 or on Ebay for half that. You need a flange kit ($10) and some copper fittings to hook it up to the piping. Somewhere you've got to come up with some 3/8-to-1/2-inch adapters.

As I said earlier, you'll need a pressure-relief valve ($15) and an expansion tank ($30) as well as a temp/pressure gauge ($15) and probably an air scoop and maybe an aquastat to control the pump. Ignore this stuff at your peril, but the pressure relief valve (a 30 psi boiler valve, NOT a 150 psi hot water heater valve; they look the same) is an absolute necessity.

 

[Peter B.]

You can pick up a Taco 007 at Home Depot for about $70 or on Ebay for half that. You need a flange kit ($10) and some copper fittings to hook it up to the piping. Somewhere you've got to come up with some 3/8-to-1/2-inch adapters.

As I said earlier, you'll need a pressure-relief valve ($15) and an expansion tank ($30) as well as a temp/pressure gauge ($15) and probably an air scoop and maybe an aquastat to control the pump. Ignore this stuff at your peril, but the pressure relief valve (a 30 psi boiler valve, NOT a 150 psi hot water heater valve; they look the same) is an absolute necessity.

Thanks once more, Eric...

The 'project' will not be undertaken lightly and I don't plan to attempt it until next season... if then. I will definitely do some more homework before I try this.

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For what it's worth, the old Round Oak has been internally modified for (somewhat) improved combustion efficiency, safety and emissions reduction. It's not in the same league (by any stretch) as an EPA stove or a gasifier, but I've enjoyed the 'ell out of making it work a little better for my needs.

You mention cold winters, Round Oaks and Wisconsin in your past... care to elaborate?

Peter B.

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[Eric Johnson]

My grandfather had one in his seed store in Waupaca until he retired. Then my folks took it out to their tree farm in Coloma, and we heated with it for several years when I was in high school. When I graduated from UW-Madison, my wife and I moved to the tree farm while I looked for a job and cut pulpwood on the side. I think that's the year it got down to -40 on New Years Eve and all the pipes froze up. Some stayed that way until Spring. Anyway, I cut a lot of wood for that stove over the years.

I've never seen a Round Oak out here in the East, but you don't see that many in Wisconsin these days, either. Maybe it was a regional brand. When I was growing up, it seemed like every farmhouse had one. Incidentally, I think what kills/cracks them is overfiring, not heat differential. Cast iron is pretty durable stuff.

 

[LeonMSPT]

"Round Oak"... almost fell over two weeks ago. Walked into an old farmer's living room in Athens, Maine and he's got the one that was in the house when the bought the place many years ago.

He told me they used to heat the entire house with it. He got sick of getting up a couple times and decided to fill it with wood and, "close 'er up fer the night".

Well... apparently this isn't the thing to do with a non-airtight stove...

They woke up to a hellacious racket, and the smell of "HOT"... their bedroom was right off the living room, and he said it looked like the morning sun was glaring in through the drapes, but it was only 1:30 am... the "Round Oak" looked like the sun when they walked out of the bedroom. Scared the hell of out them, but no damage to the stove or anything else. "Lemme tell yah. That were the last time I pulled that little stunt, mistah."

They've even still got the little statue that sits on top of it...

I've been curious about the history of them. It looks like a heck of a unit for its time. They had it burning the last time I was there. Definitely throws off some BTU's.

 

[waynek]

Peter B., you mentioned modifying the inside of a Round Oak for efficiency. I would be most interested in the details as I fire two Round Oak D - 18s.

Thank you

 

[Ugly]

Interesting thought for a DIY let us know.. please... how it goes, I'm interested in how it ends up... maybe you could market a little heat exhange setup plan to the air tight wood stove people to heat their hot water....boiler in a box

I pulled a similiar stunt using copper around an exhaust manifold with good success until the engine vibrations wore a hole through the copper. The first times I experimented with a hot water circulating system based on waste heat pickup, the smallest pump I had around was an armstrong 2HP three phase at 150 GPM... so I went to the dump and pulled a pump out of an old dishwasher and just cut the voltage to it to slow it down. They take a lot more heat than you'd think, I used the same set up later and sucessfully drew waste heat off the catalytic converter after removing it's heat shield (no vibrations there) with great success.

Mind what what was said above about pressure relief and expansion tanks..... kablooey is an awful noise....

 

[waynek]

Peter B., you mentioned modifying the inside of a Round Oak for efficiency. I would be most interested in the details as I fire two Round Oak D - 18s.

Thank you

Peter B., please disregard my request for more information... I researched and read some of your posts on the subject.

 

[Peter B.]

LeonMSPT:

Here is a link to a brief history of Round Oak stoves.

(broken link removed to http://www.swmich.edu/museum/roundoak.php)

Sorry I didn't reply sooner... my attention span (and on line presence) waxes and wanes...

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jackpine:

See my post in reply to yours in the Hearth Room...

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Ugly:

I'd still like to extract some (more) heat from the flue just after the catalyst, and have thought about fooling around some more in that sandbox... but this season, I'm still working toward improved combustion efficiency, and won't likely get back to 'hydrodynamics' til next season.

Or... until the next free moment when weather permits.

Peter B.

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[Fred61]

Back in th forties and fifties my father was a farm equipment repairman and he took me on service calls with him frequently. More often than not he found the farmer in the barn and not in the house. On occasions when we were invited into the house there was usually a Round Oak cranking away and the temp. in the living space was usually about 90* - 95* and the kitchen always smelled like apple pie.

I've tried heating water with a copper coil applied to a wood stove and the usable heat I got wasn't worth the money that I spent to purchase the hardware needed to build it. The coils I see in the photo are wrapped around the coldest part of the stove and even if they were around the hottest part you would need to fire the stove so hot to get any usable hot water that you would not be able to stay in the same room.

As for your concern about cracking the casting, don't worry about it. The conducting surface of the coils is a very small footprint.