Wood stove radiant heat!??!
 

Hello All!

I have a 1400 square foot house in Wisconsin, USA. It is a one and a half story, in which the living room and kitchen is just one room with a vaulted ceiling and the upstairs on the other half of the house is an upstairs bedroom.

I have a small cast iron wood stove in the living room. The floor is hardwood, with tile in the bathroom.

I love the woodstove and the heat from it, but would like to get some of the heat into the rest of the house, especially into the cold floor.

My house sits over a clean cement and block crawlspace. Most people in this part of the country have full basements. I couldn't because of hight ground water levels - I am just a block or two from a lake.

I am considering the idea of some sort of modified hydronic heat. If I can run heat from my woodstove to some hot water pipes, then run those under the floor of the kitchen, hall, and bathroom and back, then I can spread out the heat from the stove and have nice warm floors.

I have only ever done really basic plumbing, but am not afraid to experiment.

I am generally thinking that I need some sort of heat exchanging device on the back of the woodstove, maybe an old car radiator? Then a small fluid pump to pump the water through the system, and copper pipe, or maybe PEX to run under the floor.

I would like to keep this really simple - use water, not antifreeze, and not have an expansion tank. I would also like to keep it as affordable as possible.

Does anyone have any suggestions or links to information on something similar to this?

Thanks in advance,

-Ben

Can you run air ducts? I would think those with fans would be the easiest way to distribute heat.

I have a central natural gas furnace. That uses the crawl space as the main cold air return.

Right now, if I just turn on the fan feature on the furnace, it does even out the temperature in the house a bit, but it is moving a lot of air and is rather loud.

I love how the woodstove makes nice quiet heat, other than the pleasant crackling sounds, which I like.

I would also like to get the heat as directly into the floor as I can, so fluid pipes in the floor seems like the way to go.

I would also like to get some thermal mass going in my system. The woodstove is pretty small, so it heats up and cools down pretty fast. If I had a drum of hot water in the crawlspace, it could potentially give off heat for hours after the fire is out.

It would keep more heat around longer if you can a storage system to distribute the hot water from, but it's too much of a pain IMO. Surely a quiet circulatory fan would be cheaper than another set of pipes running through the floorboard? Unless the liquid system was way cheaper than another fan and better insulation I wouldn't bother, but that's just my two cents.

I'd do a lot of surfing, or buy a book on in floor heating. I'm sure it wouldn't be complicated to do. But, those resources will at least tell you what not to do and that'll save you a boat load of problems.

Wow, Wisconsin. Milwaukee, no less. I envy your real winters (don't get much of that in E. TN) and cheese curds. I lurves me some cheese curds.

Is your crawlspace insulated? I'm assuming it must be, since it's part of the air return plenum. That's good. We're learning that crawlspaces pretty much everywhere should be considered part of the house envelope and should be sealed, insulated, and conditioned along with the rest of the house. Knowing that, I can make this recommendation: the radiator idea is workable. You don't have to have antifreeze running through the loop, since the crawlspace is conditioned space: it should never go below freezing.

The bad news: an actual radiator isn't your best choice for getting heat out of the woodstove and into your coil. What you want is a big, flat, full-contact plate with coils running through it either attached directly to the woodstove, or coils inside the woodstove itself. I'm not positive how you would go about doing this, but one way to start is to construct your coil according to the size of the woodstove surface you intend to use, form up around the perimeter of that surface, and then pour a monolithic slab of stucco mix directly on the woodstove. You will need to do this when the weather is warm so you can orient the woodstove, and you will need to provide a means of attaching the slab to the woodstove, since masonry products don't generally adhere to metals well. Once that's done, it's a simple matter of running the coil to wherever you want the radiant heat.

Warning: concrete and stucco stick to aluminum pretty well, but I don't recommend you rely on it for attachment if that's what your stove is made of (and I don't know of any that are) - the differences of thermal expansion would probably crack your collector plate pretty badly, or cause stove warpage.

Get a plain ol' box fan and set that near the stove, set on Low. It won't make a lot of noise, but it will get a lot of heat off the stove and around the house. Another fan that blows cool air along the floor from a cold part of the house toward the stove will tend to push warm air along the ceiling toward where that fan is: also very good. I haven't had much luck getting that to work in my house from the second level, though, and mine is also a 1.5 story.

Good luck - there's lots of interesting things to do with your situation, some of which you can do immediately for really low outlay and surprising results.

With an open system (no expansion tank) you'd need a non-ferrous pump (SS or bronze) and some open area so that the water can expand and contract without bursting pipes.

Better to use a small expansion tank... although if you could do a simple gravity loop then you could skip everything (pump included) but you'd have to provide a continuous piped path up and then back down for the water. It could handle smaller laterals but no dips or they'd form thermal traps.

Thanks elhigh,

Yep, the crawlspace is an insulated, integrated part of the building. I wish there was insulation beneith the concrete slab too, but the only people who usually do that are the passive solar folks. Also there are some pretty severe drainage issues here to with me being so close to a lake.

My brother joked with me a while back about just pouring concrete over the top of the stove. I laughed it off, buy what you are suggesting sounds like a fair idea.

I do have a heat shield that goes on the back of the stove. It is just plain thin sheet steel, designed so that you can legally have the stove fairly close to the wall. I could possibly use that as the base for a concrete and copper tube heat exchanger or at least a template for one.

The design of the stove is not a good one to try to fit heat tubes through the firebox. It does however, give me the idea of maybe wrapping copper tubing around the chimney pipe, right where it exits the stove.

That part is always super hot. I can not imagine a copper tube wrap causing enough temperature drop to cause any creosote problems.

I have seen designs for DIY heat exchangers between hot water going down your shower drain and cold water coming in to your house. This would be the same idea. Reclaim some of the lost heat and use it elsewhere.

I saw a great photo once of an owner built house. There was 3-foot diameter concrete sewer tube running vertically straight up the middle of the house. It was the main pillar support and the woodstove metal chimney ran right up the middle. The space between the chimney and concrete was filled with tons and tons of sand. The support column was a warm concrete radiator all winter.

Hi Who,

I guess thermosiphoning works great, but the main disadvantage is the storage tank needs to be above the heat source.

Unless I want a 55 gallon drum on stilts in my livingroom, that isn't going to work.

I was thinking that a water tank in the crawl space with some sort of partially open top would work for both thermal mass and pressure control.

Then all I need is a pump and some tubing to run to the places I want warmed.

Thanks for the comment on the "non-ferrus" pump. I remembered you have to do something a little different for an open loop system, but I couldn't remember what.

I like to draw house designs for fun; a big solid masonry chimney is a typical defining feature of most of my designs. Like your sewer pipe example, mine is for structural and thermal service.

I don't see any major headaches with wrapping tubing around the vent pipe - you might have to clean your chimney an extra time or two per heating season, but that's about it.

The heat shield on the back of the heater would be completely replaced by the heat exchanger - while the heat exchanger is pulling heat from the stove, the plate would probably be safe to touch - hot, like a teapot: you can touch it, but not for long. And it wouldn't set anything on fire.

Try laying a lot of Styro slab insulation directly on your crawlspace floor. It ain't cheap, but once it's paid for, it's paid for. The dollars that go into heating it go right back out again, soaked into the ground under it.

Yeah, I think I will be insulating the crawl-space with rigid foam this summer.

I am mostly limited by the size of the small access panel I have into the crawlspace.

But once it's insulated, should keep the place warmer all winter.

I saw something on the internet a couple years ago called hydro-coil. It was a heat exchanger you put into the firebox of a wood stove. I could not use it because my woodstove is too small.
I just did a search again for it and came up empty.

My neighbor was talking with a pellet stove maker and they claim to be coming out with a line of pellet stoves with a built in water heat exchanger. Sorry, don't remember the brand.

Yeah, I have heard of those before.

My stove is tiny - it barely has room to put wood in it, let alone a water-pipe coil.

It sounds like the best way to go is to wrap a coil of copper pipe around the base of the chimney pipe.

I measured my crawlspace, how many feet of insulation I would need, and the cost.

It looks like for about $900 I could fully insulate my entire crawl-space (think a concrete basement that is only 2-feet deep), using rigid pink foam.

Right now, the crawl space is pretty cold - 55 degrees? That is where all the air for the furnace comes from, and all the air from the cold air returns go to.

If I fully insulate the walls and floor of the crawlspace with 2" of extruded polystyrene, I should be able to have it the same temperature as the rest of the house.

Then I will start saving on my gas bill the rest of my life (or however long we are at this house)

I should also be able to set up some hot water in the crawlspace for my Polish Hydronic System.

You may want to consider using PEX tubing stapled to the underside of the flooring - above the insulation.
And you'll need a Taco pump such as the 007-F5, expansion tank, fill valve, shutoff valves, air separator, thermostat, and I'd probably use Prestone RV antifreeze just in case you leave the house unheated at anytime.
But and the big but here is you need to know how many BTU you will be getting from the wood stove in order to design the system properly and to know if it'll actually produce enough heat to warm the floor.

I was definatly considering PEX tubing.

As for all the other parts, they get complicated real fast.

I would like to do a system similar to the "Solar heating plan for any home" in the Dec2007/Jan2008 issue of Mother Earth News.

It is an "open" system using a 4000 gallon tank built from 2x4s, plywood, and rubber roofing.

I would use fairly simply thermostats/pump controls for the project. Unfortunately, I would have to use the bronze Taco pump, which costs 2 and half times more than the cast iron one.

The other upside to a simple heat source running to a big box of water to some PEX in the floor is: I could add other heat sources to the design easily - such as a couple solar panels.

don't use prestone in a heating system... ever

there are antifreezes made for heating systems although any antifreeze reduces how many BTUs each unit of water can carry...

Because everything would be inside the house, and insulated, there would be no need to use anti-freeze. I would keep it all just plain water.

Plain water carries lots of heat, and it easy to add to, top-off, etc.

you are lossing heat up your chimney, lets say your chimney loss is 30% of your heat from fuel, if you have a heat exchanger on the back, top or side of your stove, you are still loosing that heat up your chimney, that is why those air heat exchangers that go in the stove pipe and blow air thur work so well, and seeing as how one of my side jobs is cleaning chimnys, I would advise you to check it more often if you do anything to capture that otherwise lose heat, as creosoot buildup can increase, but with a straight run of chimney it's easy to check and should be done once a year, more often if you add stuff like you are talking about.

between useing ridgid foam, and spray foam, you should have your crall space really well sealed, insulating it from the outside is alwas but invalves more work as you have to dig down a foot or two all around your house, but for example, I did a 25 streach of wall, 2 feet down by my self in about 5 hours, that way the mass of your house foundation stays warm, insted of cold.

I feel your pain, dude. I too have a wood stove. It is an old fisher Papa Bear. Good stove – excellent quality materials and workmanship. Problem is that it was designed and sized for the house before I did the Bob Vila thing to the house. Before I renovated the stove was OK in the great room. But the house was almost completely uninsulated, so when I renovated, I insulated the house like a thermos bottle. Now the Papa Bear runs me out on all but below-zero days. The stove has so much heat transfer area (stove is about the size of a desk) that if you build a small fire it goes out – snuff by heat removal. If you build a fire that stands up to the heat removal you have a blast furnace and it runs me out of my well-insulated great room. This rascal is quite capable of eating up a cord of firewood in four days if I could get the heat to the rest of the house.
What I’m thinking of doing is welding some PlateCoil http://us.tranter.com/phe/platecoil/platecoil.htm onto the back and side of the stove. I would use a hydronic pump to move water heated in the PlateCoil to coils under my bathroom floor. Or alternatively a fan coli unit in some other room. I have a basement so this is easy work.

Just a matter of moving the heat where you want it.

the furnace fan should have several speeds, select the highest speed compatiable with your noise requirements. run the fan 24/7, remember the heat from the fan motor stays in the house its not wasted. the fan should be 240v for max efficiency. insulating the crawl space is worthwhile, seal air leaks first with foam, you mentioned you have a high water table, it doesn't get any better than that, you have an unlimited supply of heat right under your feet. geothermal heat pumps are very efficient. you get 3 to 5 times the heat out from the energy you put in. the heat pump is in the air handler so that heat stays in the house also, you can use your NG for backup. the geothermal heat pump is ideally suited for northern climates and it heats your hot water all year round but almost for free in the summer if you air condition for temperature or humidty. climatemaster is one company, there are many now. these systems are no more difficult to install than central air. there are slinky coils that can be buried in a trench,shallow well, or lake. i can see the time when wood burning outside of power plants will be discouraged if not out right illegal. you could be losing more heat up the chimney than your gaining unless your combustion air is automatically controlled and comes from outside. reguardless of you heat source non toxic antifreeze (like sierra) is required in any system that could leak on the ground, treated water has scaling concerns, and freeze protection is a must in your climate. sorry, a good news/ bad news viewpoint.

Wood stove data update:

It's colder than a well digger's butt here on the frozen steppes today, so I have the Papa Bear stoked up.

I got an infrared thermometer and checked the temp of the sides, back, and top.

Depending on have much you have it stoked the surface temps varied between 390 and 550 degrees F.

The PlateCoil idea looks more and more valid.

http://www.woodlanddirect.com/core/m...747419908b3954

http://www.vermontcastings.com/catal.../photo/818.jpg



I have a magnetic thermometer that I stick to the lower end of the chimney pipe. (photo is just one similar to what I have)

The "burn-zone" markings on it range from 300 degrees F on the low end to around 575 on the high end.

Temperatures lower than that are marked "Creosote", and higher than 575 is marked "overfire".

If I had a copper coil of water wrapped around the stovepipe, all I would need to do is stoke up the stove a little higher. It is really easy to overfire my stove if I don't watch it.

I stopped by a place today where a guy had a BIG Vermont castings stove. Mine is the smallest model, the Intrepid. My Dad has the medium size, and this guy had the big one. That big one cranked out heat! It has a large flat area on back that a heat exchanger could attach to.

Some new pellet and coal stoves have stainless steel water heating coils.

Just want to give an option for brazed plate heat exchangers:
Heat Exchangers - Online

I saw a very clever wood stove built on the cheap in a muffler shop a while back.

Imagine a 55 gallon drum built for the firebox, with another 55 gallon drum on top with 2 very large exhaust piping pieces allowing the smoke to go into the upper drum (which is sealed off) then a generic stovepipe attached to the upper drum heading outdoors. I asked the muffler shop owner about it (it's a one man operation) and he said he recorded a 90 degree F temperature on the output (I assume with an infared thermometer.) Apparently he kept his underinsulated shop comfortable with this rig.

I've also read how Russians have very convoluted chimnies to capture as much heat as possible. I suppose they invented the geo mass concept (go ruskies)

My point being the simplest heat extractor would use heat from the smoke. If you downsize the pipe as you extract more and more heat you can keep creosote down to a minimum, or you can design everything assuming creosote is going to build up and make it safe to have an occassional chimney fire (insulated pipes in the house, a long pipe on top that vents the fire safely.)

Or you could have a planned cresote burn where the exchangers are turned off and you put in some dry oak and hickory to make the chimney fire happen when you expect it.

Just some random thoughts, dispose of the useless info :D

The two-barrel stove is sometimes called an Alaska heater. Stotz sold a kit for making them.
The Russian masonry stove was one of the first things thtat one was supposed to be licenced to build properly. You didn't want to have one fail mid-winter! It was based on having brief, hot fires heating the thermal mass, which would provide constant heat without the creosote buildup and waste smoke of an airtight stove.

I'd like to build a wood stove using a car turbocharger to pressurize the firebox. In effect, you'd have a gas turbine with solid fuel. At high pressures, you could get some power out, but even a few PSI to keep the fans turning would let you condense the steam from the smoke for a big efficiency gain, and install a cheap vent instead of a chimney.

Another thing that could be done to help store the heat energy is to place a rock slab or large rocks on top of the stove. The material will slowly absorb the heat and give it off after the fire is out and the metal has cooled.

You could also use the stove for the burn chamber of a rocket stove I wish I had some pictures of the one my father-in-law did at his cabin. Just to make it easier to find for future reference here is the build he did with fire bricks in his house. Rocket Stove | Northern Kentucky Landscaping from The Good Earth, Inc.

This whole couch heats the house and it nice to warm up on when its cold out.

You need to be careful about the rocks you use...some can explode if heated too hot. :(

I think that the issue of the rocks exploding is from the rocks being cold/wet and then being quickly heated not the type of rock but I could be wrong.