Outdoor wood boiler wood requirements

[BLSXJ]

your boiler or furnace converts chemical energy into heat...... your home losses heat from all 6 sides.... its really as simple as chemical (wood or gas) IN... HEAT out.

if you replace a 90% efficient forced air furnace with 90% efficient boiler.... your going to burn the same amount of the same fuel, because your losing the same amount of heat.

 

[Groo]

your boiler or furnace converts chemical energy into heat...... your home losses heat from all 6 sides.... its really as simple as chemical (wood or gas) IN... HEAT out.

if you replace a 90% efficient forced air furnace with 90% efficient boiler.... your going to burn the same amount of the same fuel, because your losing the same amount of heat.

yes, but efficency is measured under ideal conditions. How close do the 2 types of heat match ideal conditions. a wood boiler can be designed to match it fairly well if it has a thermal resivior, but most wood boilers have very inefficient burn chambers. The other inherent innefficency with a wood boiler is that they are usually outdoor boilers, so there is heat lost to the environment before it even gets to the house. In general wood boilers are sold on their capacity, not efficency.
A problem with putting the heat into pex coils in the floor instead of a baseboard or forced air heater is that the heat exchanger is is surounded by concrete in the floor. heat radiates around. there is more insulation going down, but there is also the concrete insulating the coils from allowing the heat to go up.

If you have an efficient indoor boiler that stores the heat (allows the boiler to blaze at peak efficiency then slowly dispense the heat) inside, then use baseboards or forced air, you would have a much more efficient system.

 

[BLSXJ]

yes a outdoor wood boiler will lose heat to the environment before it delivers that heat to the house (the amount depends on installation set up).

there is some fundamental differences between heating with convection (hot air) and radiant (hot surface) heat. generally with infloor heat, you can set the temperature lower, which reduces your heat lose, because it reduced the temperature differential between the building and the outside environment.

the original poster asked how much wood will he need... he posted information on how much energy it took last winter.... I converted from money spent on gas, to btus then back to wood.

 

[teejk]

yes a outdoor wood boiler will lose heat to the environment before it delivers that heat to the house (the amount depends on installation set up).

there is some fundamental differences between heating with convection (hot air) and radiant (hot surface) heat. generally with infloor heat, you can set the temperature lower, which reduces your heat lose, because it reduced the temperature differential between the building and the outside environment.

the original poster asked how much wood will he need... he posted information on how much energy it took last winter.... I converted from money spent on gas, to btus then back to wood.

OP stated that he already has the in-floor tubing and is merely changing the heat source so I agree that there is no need to talk him out of radiant in-floor heat. Thanks for bringing the topic back to the original question. Btw I have in-floor in cement in my shop and under-floor in the house...I doubt there is any measurable difference in cost to operate vs. forced air or baseboard but there is a difference in over-all comfort. Radiant heats objects and something in the brain says if your feet and legs are warm your whole body feels warm.

 

[Groo]

Clearly, not asking the OP to tear out his floor, I was just explaining the ineficencies I saw in the ststem as the bassis for my estimate, and everyone jumped all over me.

ps. even "radient heat" is convection heating. The convector is the floor surface instead of some copper fins.

 

[teejk]

Clearly, not asking the OP to tear out his floor, I was just explaining the ineficencies I saw in the ststem as the bassis for my estimate, and everyone jumped all over me.

ps. even "radient heat" is convection heating. The convector is the floor surface instead of some copper fins.

I don't think anybody is jumping all over you. I don't think there is any consensus on heating a house. I would agree with you on the radiant/convection "conversion" but my heating/plumbing friend says I'm wrong.

 

[donaldj]

I've researched this for a couple years and did quite a bit of digging before investing. Radiant heat is far more effective than forced air.

First, we have a finished area in our basement and spend some time there. Secondly, heat does rise and will eventually warm both floors very evenly. The trade off is that with the thermal mass in the basement slab, you don't have immediately adjustable heat.

Radiant heat effectiveness is achieved because the heat is at floor level, where we are. The air near the floor, where people dwell, is thus warmed up first, and because this air isnt disturbed (except by our movement), the usable area gets the heat. Furthermore, because the heat source is low, items like furniture and other things absorb the heat more readily and add to the available thermal mass.

With forced air, hot air is blown into an area, which heats it, but because it is blown in, air currents more readily take the warm air high in the room (less effective heating) more quickly.

Some other points asked:

• I do not plan to have an auxiliary hot water tank in line with the boiler (yet).
• We have a natural gas furnace. I'd rather it never turn on.
• I will be putting a couple heat exchangers in the furnace plenum for hot air on demand if we need it.
• Radiant heat is amazingly consistent, even though the fire may not be. My research indicates when ramping up in the Fall, it will take 3-4 loads of wood a day to heat up the slab. The fan on the boiler is controlled by a thermostat, and turns on to oxygenate the fire when needed. Otherwise, it's on just low enough to keep a smolder going. The thermal mass of the slab, though, is such that heat content is very consistent. Once warmed to steady state, it will take 2 loads a day. I can easily add wood in the morning, when I get home from work, and just before bed. I'm up and about during these times anyways.
• Thank you for the propane lighter suggestion. Looking into that now.
• BLSXJ, your math was awesome. Thank you so much for the time put in.

Thanks for the advice, all! I'll keep cuttin and splittin

 

[BLSXJ]

BLSXJ, your math was awesome. Thank you so much for the time put in.

no problem... glad I could help

 

[teejk]

I've researched this for a couple years and did quite a bit of digging before investing. Radiant heat is far more effective than forced air.

First, we have a finished area in our basement and spend some time there. Secondly, heat does rise and will eventually warm both floors very evenly. The trade off is that with the thermal mass in the basement slab, you don't have immediately adjustable heat.

Radiant heat effectiveness is achieved because the heat is at floor level, where we are. The air near the floor, where people dwell, is thus warmed up first, and because this air isnt disturbed (except by our movement), the usable area gets the heat. Furthermore, because the heat source is low, items like furniture and other things absorb the heat more readily and add to the available thermal mass.

With forced air, hot air is blown into an area, which heats it, but because it is blown in, air currents more readily take the warm air high in the room (less effective heating) more quickly.

Some other points asked:

• I do not plan to have an auxiliary hot water tank in line with the boiler (yet).
• We have a natural gas furnace. I'd rather it never turn on.
• I will be putting a couple heat exchangers in the furnace plenum for hot air on demand if we need it.
• Radiant heat is amazingly consistent, even though the fire may not be. My research indicates when ramping up in the Fall, it will take 3-4 loads of wood a day to heat up the slab. The fan on the boiler is controlled by a thermostat, and turns on to oxygenate the fire when needed. Otherwise, it's on just low enough to keep a smolder going. The thermal mass of the slab, though, is such that heat content is very consistent. Once warmed to steady state, it will take 2 loads a day. I can easily add wood in the morning, when I get home from work, and just before bed. I'm up and about during these times anyways.
• Thank you for the propane lighter suggestion. Looking into that now.
• BLSXJ, your math was awesome. Thank you so much for the time put in.

Thanks for the advice, all! I'll keep cuttin and splittin

Probably more than 1 day do heat the slab (you don't want to push that too hard because bad things can happen). I have radiant in concrete in my shop building where the LP source does not exceed 160F. I figure it takes 2-3 days to bring it up to normal in the fall. But your point about radiant vs. forced air I have to agree with (we have it in the house also but a "hanging" underfloor system). It is indeed "nice" heat...no hot/cold spots and is easier to zone than forced air I think (manifolds and circ pumps vs. dampers).

 

[donaldj]

I have a huge basement. I anticipate about 7-10 days to heat the slab.

My boiler will be set to 180F, and I will have a mixing valve to reduce in-slab temp to 110-120F, as needed to make near-floor temp approx 85F. Within 2 weeks, that extra heat radiated into the basement will permeate through to the upstairs. We know we might have to forego the living space down there in winter if it gets too hot. We have an entire upstairs for that if needed. Peoples' theory aside, I have a friend with a similar setup and his furnace only comes on a bit in the fall (we've had some abrupt fall to winter transitions here).

I will be getting an underfloor system for the first floor eventually. I have an oversized boiler anticipating that, water heater, a bonus room above the garage, and potentially an outbuilding.

My boiler is a gasifier system, and has a lot of soapstone-like mass in it, so it smoothly heats the water and retains the heat generated for quite some time.