Wood boiler type/brand for garage heat
I’m looking at a couple used wood boilers to heat my garage with. currently using a wood stove, but want to take advantage of the radiant floor option I installed when pouring the floor.
building: 2 story 24×36 gambrel. floor is 6″ w/ 2″ EPS underneath. 1/2″ pex on 12″ centers, 3 zones.
heat loss calc runs about 50K BTU/hr. Probably less as desired temp doesn’t need to be as high as a home.
1 boiler is Itasca 85K BTU unit w/ 20 gallon capacity. unknown vintage.
Other boiler is New Yorker 120K BTU w/ 22 gal capacity (1981 vintage).
I’ll use these intermittently, so I’m thinking the higher capacity unit would be better to be able to heat things up more quickly when the garage has cooled down. Might want a forced air radiator for the quick heat, then switch to floor once air temp comes up.
Probably won’t hook up the unit until this summer, and will deal w/ control issues at that point. Just trying to decide which (if either) of these units I might grab while they’re available fairly cheap.
Any comments/suggestions?
Thanks
Don
Replies
I have a 40 by 42 building with gambrel roof which I heat with Woodmaster boiler. I follow your specs. pretty well till I get the the capacity. I think mine is somewhat near 150 gallons. I don't see how you could get along with only 20 gallons.
I don't heat the loft but do get a lot of leakage to the basement since there is no insulation between the two floors. I don't know the BTUs of mine but it seems to heat it nicely in all kinds of weather. I don't think it is all that efficient but wood is cheap in these parts so not too much of a concern.
You will need a mixing valve for in floor heat. Mine was installed with a manual MV that I replaced with a thermostatic controlled one after a couple years and what a difference. Manual - 24 hours to heat up, thermostatic - 4 to 6 hours. Your idea of an alternate forced air radiator sounds good if it isn't too expensive. Best of luck. Keep us informed.
Tinkerer,
I'm assuming that 20 gal. capacity is of the water jacket of the unit itself. I believe a lot of people add a water tank to store heat. In this case, I'm hoping that the floor itself (14 yards of concrete, which by my calculations can hold over 10,000 BTU's per degree F of temperature rise) should provide the thermal storage.
Is yours heating a concrete floor (large thermal mass) or under a wood floor?
I'll definitely be looking hard at the control scheme once I get closer to that part of the process.
I think it was Junkhound who mentioned using a truck radiator for an air heater. Should be able to set that up pretty cheap.
Don
Well yes, you would seem to have a somewhat different setup than I. Mine is a six inch concrete pour and since it is a suspended floor, it has a lot of bracing. If my heat goes out during the night, the temp really doesn't go down much for a day. Probably more mass in that floor than the average house.
I hope you didn't staple the heat tubes to the foam and then pour 6" of concrete over it??
tubing was tied to the reinforcing mesh, which was (mostly) pulled into the middle of the pour.
You did it the right way!! I know a guy who just completed a building similar to yours, but somewhat larger. He has the 6" floor with the tubing stapled to the foam.
His bill last month was $3000 for propane and his feet are still cold, and so is the building for that matter.
His engineer approved and designed all of this!
Sounds like there's more to it.
There was a discussion here probably a year or more ago regarding whether it's better to have the tube down on the foam or in the middle of the slab. General consensus (including a lot of references to sophisticated thermal models) was that middle of the slab was theoretically better, but shouldn't be a huge difference.
Your friend should be looking hard at how well sealed and insulated the building is. Also, is the water table high around the building, so that water is up around the slab, keeping the insulation from doing its job?
Don
There is something else going on there besides a couple inches of difference in the elevation of the pex location. He has a bad meter, a leak in the gas line or the pex fittings, or a stream washing through right under the slab, or a window open
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I agree that it's probably not all the fault of the way he installed the tubing, but installing tubing like that is a really, really bad thing to do. I haven't seen the work yet, but I would guess there are other issues too.
On two occassions, I have demo'd areas with heat tubing installed that way. If you could see what the bottom of one of those slabs looks like, you would never let one of your clients install tubing that way.
It's kind of like the guy who leaves the reinforcing mesh on the bottom of the pour and you just peel it off the slab when you dig it up and use it again. It's the same way with the tubing. Very minimal contact with the slab.
Most of these thicker pours use regular coarse aggregate for strength and the stones tend to gather over the tubing, reducing contact even more.
Thanks for those observations
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for that setup, I would just use a water jacket on the wood stove to supply heated fluid to the floor. That way, you get free heat and the flywheel effect of the storage in slab, plus the instant heat when you fire up the stove without a modine radiator above.Â
edit - dhuh - I just now see this thread title already says WOOD boiler.
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Edited 1/4/2009 2:02 pm ET by Piffin
Not really a dumb comment - Do you know how much heat most standard wood boilers give off directly to the room they're in? If it's significant, then I'd get the instant heat benefit without having to add a modine type unit.
Another option I've got, which I'm going to look at again tomorrow, is a setup which I think is more of a wood stove with a couple coils in it. This would probably do the dual-purpose thing pretty well, and I can get it dirt cheap. I looked at it a couple years ago (retired coworker used it for several years, but it's been sitting unused for a few more) Wasn't ready to put heat in the garage at the time, so I just kept it in the back of my mind.
The fun part will be setting the system up safely, so that if the circulator stops for some reason, I don't start generating steam & pressure. A few years ago I lived in an apartment which was heated similarly. The circulator quit, and even though the boiler was in another building and piped underground, the water boiling in the pipes at the boiler end made it sound like a war in my apartment.
Don
when i built my house i put radent tube in in my slab in the basement which has 2" blue board underneth and the tubing is tied to rebar in the center of the slab 12" on center and baseboard heat upstairs and i use a central boiler classic model cl5648 wood boiler once the slab heats up it takes 24hrs to cool down.....i'm building a 32x40 garage this year with a gambrel roof with a wood shop upstairs with the same setup i think its gonna work just as good as in the house to me its worth the investment but i do have a woodlot so my wood is free except for the labor and the taxes on the land i use 10-12 cord a year.....Chris.....
How much did you Central Boiler Classic cost you? How long ago did you buy it?Karl
i think i paid around $4000.00 for it including 100 ft of tube to house and taco pump and fittings not including backhoe work which i did ....i bought it 4 years ago .....Chris.....
Sounds intriguing at that price. I suspect it is illegal to sell them in California and shipping would be costly. With a little creativity I am sure I could figure out how to purchase one and it would be cleaner than the old Jotul stove we are burning around the clock.I have a thousand feet of basement with pex looking for a heat source and virtually unlimited firewood.Thanks,
Karl
don't know how it is in California i live in upstate new york and mine is going 365-- 7 days a week i also heat hot water with it.....i also know someone who built his own and i guess it works good .....Chris......
Another question for those who play with radiant calcs:
How much heat can my slab absorb in BTU/hr? I don't want to get a boiler which can put out significantly more energy than the system can take - not sure how sophisticated the controls are on some of these boilers.
Assumptions (someone yell if these seem out of line)
* 800sf, 6" thick concrete floor starting at 50F (14yds, 55,000# @145#/cu. ft)
* 2" EPS under slab and around edges
* fluid (glycol mix) at 140F max (reasonable??)
* 1/2" std O2 barrier PEX, 12" on center
* being conservative, let's ignore heat emitted to air on top surface of slab.
Thanx
Don
being conservative, let's ignore heat emitted to air on top surface of slab.
That of course, is where most of your BTU's are going.
What you need with a wood boiler is some type of buffer tank that holds a lot of water. This is accomplished on outside boilers by having a hundred or more gallons of water in the system.
On an inside boiler, it's not that important if you are using regular radiators, but when you are using radiant floor heat, you have to control the water temperature more closely.
If the hot water is going only to your floor, you must have a tank and control the temperature of the water in the tank with an aquastat that controls the fan on the wood boiler.
If you have other regular radiators, you can use a mixing valve.
What you need to do is calculate the heat loss of the building and then check the specs on your wood boiler to see if you can provide that much heat.
If you have a boiler that is too large for just the room, consider heating domestic hot water or maybe a snow melt system etc.
We hardly ever work with indoor boilers anymore, but the outside boilers are very good at controlling water temperature.
>What you need with a wood boiler is some type of buffer tank that holds a lot of water.
I'm hoping that I can accomplish this effect just using the slab as the buffer. Keep in mind that this is a garage which will be heated intermittently and will almost never hit a steady state. Typical scenario I'm thinking is that I might go a day or two (or more) without heating it, then get home from work and want to work on something. Garage and slab temp may be 35 or colder.
I'd like to fire up the boiler, have it feed heat to the room via a modine unit or maybe even an old car radiator to quickly warm up the air to maybe 55~60. After that, dump heat to the slab, probably until the wood is all burned up.
If my calculations are correct, it would take roughly 400K BTU to heat the slab from 35 to 75 degrees, if it wasn't giving up any heat to the surroundings at the same time. I don't think I could get that much heat out of one load of wood in the boiler, so overall I don't think I'd overpower the system.
My main question is whether the slab can accept the heat at a rate of 120K BTU/hr. (that's what I was getting at with my post regarding slab heat capacity).
The 120K boiler is the larger one (which I just came back from looking at). It's set up with a temperature switch to control the combustion air blower for a certain water temp range (forgot to ask what that was). He also had a separate overtemperature switch which would open another heating loop if the water temp went too high. If I get this unit, I'd probably hook up the overtemp loop to the circuit I left available for an ice melt loop in front of the garage.
If the 120K boiler seems too big (I don't really think it would be), then I'll either get the 85K unit that's also available (but I haven't looked at yet) or another unit belonging to a friend which I don't know too much about as far as output.
I'm hoping that I can accomplish this effect just using the slab as the buffer.
NO,NO a thousand times no!! You have to control the temperature of the water entering the heat tubes in the slab or you are going to have all kinds of issues.
Your idea of using the Modine unit will work nicely. I have done that many times, but you have to keep the water temps in the slab to less than 140 degrees.
You can actually damage the pex as well as the slab by sending water through it at too high a temperature. This is why you need a buffer tank unless you have a considerable amount of water in the rest of the system.
You have to control the temperature of the water entering the heat tubes in the slab or you are going to have all kinds of issues.
This is basically why I was trying to figure out how fast the slab can suck up the heat produced by the boiler. If the slab (plus the ice melt loop in a pinch) can absorb the heat readily enough, then I wouldn't need to worry about the water temps getting too high. If the potential exists for the boiler to overrun the slab, then I'd definitely need a buffer system. I was hoping someone had the formulae handy to calculate this, but I can probably do the research & figure it out myself. I'd still need to go through the calculations to try to size the buffer tank.
I've looked at 2 boilers at this point - one is the 120K BTU boiler - conventional design, I believe -- the water reservoir is above the firebox with tubes running up through it to carry exhaust gases out the top. Thermostat-controlled blower for combustion air, & overtemp thermostat to open a bypass loop.
The other unit is more of a wood stove with tubing loops exposed to the firebox inside on both sides & top. No data plates, but probably capable of putting out similar amount of heat. This has the advantage (??) of directly heating the air around the stove, as it's not insulated, so I wouldn't need a Modine type unit added on. Potential exists, however, to overheat the air before the slab is brought up to temp. This unit, while cheaper to buy upfront, would need additional controls, circulator & expansion tank to match what comes with the other boiler.
My immediate concern is making a decision on the boiler while these are available at a decent price. There's also an 85K btu conventional-style boiler I haven't looked at. Once I feel comfortable that I understand the heat load requirements It'll be easier to pick the proper boiler. I've run through a couple of the online calculators which show ~ 40-50K BTU load, but I'm not positive how I'm going to finish insulating and my target temps are probably different than the calculators' assumptions. So, I need to do some more figuring.
Fortunately, I'm doing ok with the basic wood stove so far, so I have until next fall to set up the system, once I have a boiler picked out.
Don
It is very easy for the temps on an indoor wood boiler to get out of control!!!!!!!!! The reason this happens is because you are dealing with a small amount of water and there is no place for the heat to go.
You are thinking that you will dump very hot water into the loop and it will immediately cool off and everything will be fine. That is not the way it works.
It is far more common (if your loop lengths are proper) to see a 10 or maybe 15 degree drop in temperature from the inlet to the outlet of the loop.
If you dump water in there that is way too hot, you will see a clearly defined pattern of stress cracks showing you where the heating tubes are located in your floor.
If you see that, be sure to mark them clearly so you will know exactly where to dig up the tube to replace the leak that will eventually show up ;)
If you dump water in there that is way too hot, you will see a clearly defined pattern of stress cracks showing you where the heating tubes are located in your floor.
Well, the slab is now over 3 years old and doesn't have a single crack, so it's about due :)
Don
I don't think you need be concerned that the boiler will put more heat in the slab than it will absorb. When you have a wood stove inside do you worry whether it will produce more heat that the air will absorb? The fact is that we want the slab to warm up as quickly as possible just like we want the wood stove to warm the room as quickly as possible. The boiler is regulated with a thermostat. When the the water gets to a preset temp (mine is regulated between 160 º and 170º) the fan shuts off and the boiler just simmers until the system has brought down to temp again. You could have a boiler five times as large as required and it will still be regulated, you won't need to put wood in it so often and it will just be a little less efficient. Keep in mind that on a very cold day your building might require ten times as much heat as it would on a more mild day.
Now in the inside before the water goes into the floor, you should have a thermostatic mixing valve. This thing mixes in just enough hot water from the boiler with the return from the floor to give a desired temperature to reintroduce a return into the floor again. In my case, I set the thermostatic mixing valve to 125º. This gives a nice heat input without overheating the concrete to an unsafe expansion.
You have the outside unit which heats the water to preset temperature limits. When that water is pumped inside and before being introduced into the concrete floor is is moderated by the thermostatic mixer to a given temperature and then you can put as many zones as you want inside. I have two for the large rooms I have but have considered heating the bathroom and hot water also.
Edited 1/8/2009 12:12 am ET by Tinkerer3
Edited 1/8/2009 7:30 pm ET by Tinkerer3
That's basically the setup I think will work for me. The difference is that you've got an outside wood boiler with a large water jacket around it. The unit I'm looking at is an indoor boiler. The heat exchanger is basically a tank above the firebox with tubes running up through it to carry heated exhaust gases.
At 120K btu/hr, that 20 gallons or so of water can heat up 12.5 degrees per minute if heat isn't being drawn away. I'll have to do a little more research & calculations to decide if that's an issue. Probably is ok, as there is also an overtemp thermostat which I'd set up to dump to a loop outside (ice melt in front of the garage). I have no actual experience with this kind of system, so I'm going slowly. Wouldn't be too difficult to plumb in a tank to increase the buffer size just for safety.
Another boiler option I have is one which is basically a wood stove with tubes running through the firebox. That would definitely need some type of buffer tank.
Don
I'll give you a few more words of advice. There is a huge difference in the efficiency of heat transfer in these indoor wood boilers. The really good ones have cast iron water jackets surrounding the firebox and the kind you are looking at probably don't.
In your case, that may be a benefit because they don't kick out a lot of heat for the amount of fire you have.
What you want to do is, keep that thing burning steadily but not too fast. If you cycle it off and on with the fan/thermostat, you will have a creosote problem beyond belief. That is why you need to have a lot of water to circulate through the system.
Outdoor wood boilers are notorious for creosote buildup, especially if you have extended the chimney to keep the super noxious smoke up in the air instead of in and around your house.
Buying an indoor wood boiler that is way too big for your needs is going to cause you problems with cycling issues.
Buying an indoor wood boiler that is way too big for your needs is going to cause you problems with cycling issues.
That's my dilemma at this point. Is the 120K boiler going to be too big? My basic plan is to take a cold building (24x36, 2 stories), heat the air to temp and then heat the slab in a relatively short time, then let the slab keep the building warm/above freezing for a reasonable time. This indicates a fairly high output heat source is required. Exactly how big/what controls are needed are my concerns.
I'd love to get a nice gasification unit, but couldn't justify the cost.
My current stove is a homemade (maker unknown) double-barrel design (using smaller-maybe 30 gallon- heavy walled tanks. The top tank is cut in half & flat on the top. The bottom tank has a baffle on the top to direct exhaust gases from the back up over the fire to the pipe in front which goes to the top tank. If I get the unit burning really hot (slight red glow on the top of the bottom tank) it gets a secondary (gasification-like) burn going, and burns clean. Doesn't hold much wood, though, and doesn't heat the slab.
Thanks
Don
and then heat the slab in a relatively short time
You seem to be hung up on this concept. You don't heat a huge concrete slab in a relatively short period of time!!!!!!!!!!!!
When we install a new, modern gas heating system with concrete in- floor heat, it may take a day before the slab gets warm depending on how cold it was to start with.
You cannot dump high temp water into these slabs and expect it to warm up in 30 minutes.
As I told you before, do a heat loss calc on the building, figure out how much heat your slab is going to emit, and then figure out if your wood boiler is up to the job. That is the only way to plan this.
I don't think I would rely on an extra loop to take up the over temperatures. You really need an emergency backup switch to ensure the heat source is shut off .
don't think I would rely on an extra loop to take up the over temperatures. You really need an emergency backup switch to ensure the heat source is shut off .
I'm assuming that the primary thermostat would have already shut the blower off, effectively shutting down the fire. The overtemp t-stat would handle those situations where residual heat drives the water temp up too high.
The current owner had this set up in his house for many years, connected in-line to an oil-fired boiler. He had it set up to feed another floor in the house if the overtemp kicked in. Not sure how often that happened.
Don
Okay, it seems you already have the overage protection. "Not too sure how often that happened" Hopefully it never happens but one needs that protection.
don't forget to put the tubing in the middle of the slab and tie it to a rebar frame it distributes the heat better thats what i did.....Chris.....
heres a site that might intrest you http://www.radiantcompany.com/ .....Chris.....
Edited 1/4/2009 7:20 pm ET by C_Evensen