# Wood boiler wood usage for square footage



## FarmLife (Aug 1, 2017)

Hello forum members!  My husband and I have recently purchased a home which uses an outdoor wood boiler as a primary heat source and propane as a back up.  We are approaching our first season here using the wood boiler and we are entirely new to using one.  Heating is currently provided for the home, garage and water heater in the home, with propane taking up the water heating needs in the warmer months.

My question is... will we use less wood for heating if we opt to eliminate heating the garage, or would we still use the same amount of wood regardless?  We are trying to decide if we should plan to shut off garage heat for the winter as we are not likely to really need it, but if it's going to use the same wood regardless, then it shouldn't matter for us either way.

Thank you in advance for any information you can offer here.  As total newbies to using wood as a heat source, we are looking forward to feedback.


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## maple1 (Aug 2, 2017)

Well - if you are heating less space, you should use less wood, yes.

Adding a 'how much less' to that would be very difficult - there are a whole lot of factors that you have to try to account for. Then - where is the 'matter' line? If you would be saving 2 cords on 20 - would that 'matter' to you? 

Do you know how much wood the prior owners went through? That could turn out to be a surprise. How much do you have ready to go?


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## FarmLife (Aug 2, 2017)

maple1 said:


> Well - if you are heating less space, you should use less wood, yes.
> 
> Adding a 'how much less' to that would be very difficult - there are a whole lot of factors that you have to try to account for. Then - where is the 'matter' line? If you would be saving 2 cords on 20 - would that 'matter' to you?
> 
> Do you know how much wood the prior owners went through? That could turn out to be a surprise. How much do you have ready to go?




The previous owners said they would use 15 cords a season, which is why we are wondering if not heating the garage constantly would allow us to use less.  The home is approximately 1600sf (a modular put in year 2000) and the garage is not connected to the home with 2 1/2 stall with a 2nd floor storage space, but is fairly well insulated.  From what I've read in various posts here about how much some folks use (even in my own state), it seems like they used a lot more than some others.  It is my understanding that they also would use wet wood as well as seasoned, so not sure if that would affect how much they had used.

We currently have no wood for this winter but have researched sources to purchase it from and plan to do so by September.  My husband is currently collecting wood from downed trees people are looking to get rid of for free, but that will not be ready this year to burn.  Unfortunately, we have no wooded space on our 6 acres, so we have to purchase wood and find free wood when we can.


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## peakbagger (Aug 2, 2017)

This is definitely a "it depends" situation. Most OWBs are sized for the maximum instantaneous winter time heat load which means they are vastly over sized for much of the year. They can burn efficiently at full load but anytime they have to operate at partial load, they are far less efficient and potentially a significant pollution source. If you can use the garage as an "opportunity load" to be heated when there is no call for heat from the house, the boiler may be able to operate at full load longer and the additional wood would not be significant. Of course if the garage load is substantially higher than the house, then you will burn more wood. If you do use the garage as an opportunity load you will need to make sure the loop has glycol in it, just in case the slab drops below freezing or just run a very low temperature set point for freeze protection along with an opportunity set point.


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## leon (Aug 2, 2017)

The problem with not "heating the garage" is one of "broken piping/damaged pex" if the installation was not done properly.
It would be best for you to find out what type of underground pipe was used for the pipe run to the home and the garage.

I always tell folks that if at all possible to install full firebrick filling the fire box volume half full up to the flue breech and I will explain why.

When I had my wood and coal hand fed that was inside my home I cut my consumption of coal and wood in half because the fire brick
did two things; first the firebrick held the heat in the boiler and second it shed the heat it built up in the fire brick back into the firebox and burned more smoke reducing the amount of heat lost up the stack with un-burned smoke.

As a result of the installation of the firebrick it reduced the amount of wood I burned to less than half and of what I used to use which was 15 cords a year of mixed hardwoods and softwoods and when I burned anthracite coal the fire was kept hotter longer.

It would help if we knew what brand of boiler/forest eater you have as it is easy enough to lay 2 by 12 channel iron down and stack firebrick on the channel iron to act as a heat sink that will hold heat for days and also create a more efficient burn during the heating seating.
I no longer burn wood as I switched to using a anthracite coal stoker boiler after 33 years of burning wood-after falling on ice made by my firewood processors exhaust and breaking my nose I had enough.     

These boiler manufacturers still need to line their boilers with firebrick which would make a world of difference in how long the boilers would hold the heat and reduce the amount of smoke they produce.


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## maple1 (Aug 2, 2017)

Ah yes, I thought about but forgot to mention that - be very careful nothing freezes.


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## FarmLife (Aug 2, 2017)

Thank you everyone for the feedback thus far!  We came from the suburbs with natural gas, so using a wood furnace is entirely new to us and we are trying to get a feel for everything and be prepared for the cold season.

The brand we have is a Wood Master 3300 ( http://www.woodmaster.com/product/woodmaster-3300/ ).  It says it is good for up to 2000sf, but with the garage being heated, that is for sure more than this heated.  Everything here is also forced air.  Ideally, the garage heating would be useful for when my husband is working on something out there in the winter.  Otherwise, it's not really needed as the only other things out there are a few freezers and a fridge.  Though at some point, we may bring in chicks next year that will need warmth, but a heat lamp should be fine for that if we keep them in the garage.


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## maple1 (Aug 2, 2017)

Did you mean the garage is forced air also?

If everything is really forced air, that would mean there are heat exchangers in duct work somewhere - and if that is also true of the garage and there is no glycol in the system, that part would be very vulnerable to freezing. And resulting system damage. So you would need to be very careful about knowing exactly what you have - then take everything into account re. system vulnerabilities. You may have no choice but to keep everything running all winter - but we can't be sure from here. And if everything is plumbed in series, I would think that would really make it a 'no choice' thing - although, turning a distribution fan off out there while keeping the boiler water flowing might be a possibility. Just don't know...


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## FarmLife (Aug 2, 2017)

maple1 said:


> Did you mean the garage is forced air also?
> 
> If everything is really forced air, that would mean there are heat exchangers in duct work somewhere - and if that is also true of the garage and there is no glycol in the system, that part would be very vulnerable to freezing. And resulting system damage. So you would need to be very careful about knowing exactly what you have - then take everything into account re. system vulnerabilities. You may have no choice but to keep everything running all winter - but we can't be sure from here. And if everything is plumbed in series, I would think that would really make it a 'no choice' thing - although, turning a distribution fan off out there while keeping the boiler water flowing might be a possibility. Just don't know...




I checked with my husband and he indicates that the garage is not forced air, but rather a fan is used.  I assume it may be a distribution fan?  I think his thoughts were to be able to cut off the water heated supply to the garage in the future if it would save us on wood usage in the furnace in doing so.


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## salecker (Aug 2, 2017)

Just because the previous owners used wet wood... DON'T. i repeat DON'T use green/wet wood.
It doesn't help your system do anything other than be inefficient.Remember green/wet wood contains water which is the main tool firefighters use to put out fire.When trying to use wet/green wood in a wood burner you first to turn the water into steam,using your BTU's that should heat your house.This is done before your wood burner can burn the wood.Having all the steam in your firebox will produce creosote.Creosote can cause a number of bad things,like chimney fire,plugged flue tubes,ect.
 Just because you don't have a supply of dry wood,don't be tempted to use green/wet wood.
 If you are talking about using 15 cords of wood is that full cords?
 I use around 8 to 10 cords heating a 2500 sq ft house with a 25 ft ceiling in half of the house,plus the building that houses the boiler is 20x24 ft.This is using dry spruce.
 I have a gasification boiler with 1000 gals storage. Typical heating day at minus 20C.. start fire at 5 PM boiler will run wide open till 10/11PM. House draws heat from storage till 5PM the next day. Repete. If temps are in the -40 C range then the fire gets started around noon and runs till 11PM
 Heating season starts in Oct till April/May


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## FarmLife (Aug 2, 2017)

salecker said:


> Just because the previous owners used wet wood... DON'T. i repeat DON'T use green/wet wood.
> It doesn't help your system do anything other than be inefficient.Remember green/wet wood contains water which is the main tool firefighters use to put out fire.When trying to use wet/green wood in a wood burner you first to turn the water into steam,using your BTU's that should heat your house.This is done before your wood burner can burn the wood.Having all the steam in your firebox will produce creosote.Creosote can cause a number of bad things,like chimney fire,plugged flue tubes,ect.
> Just because you don't have a supply of dry wood,don't be tempted to use green/wet wood.
> If you are talking about using 15 cords of wood is that full cords?
> ...




We had a certified installer come to inspect our furnace prior to purchasing the home and he had also stated not to use green/wet wood.  We are currently collecting green/wet wood to cut and store for future use, but we will not use green/wet this year and will purchase instead.

I am not sure if 15 cords is full cords or not.  That is the reply my husband got from the realtor who checked with the previous owners.  I will have to ask him to inquire about that again.


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## maple1 (Aug 2, 2017)

FarmLife said:


> I checked with my husband and he indicates that the garage is not forced air, but rather a fan is used.  I assume it may be a distribution fan?  I think his thoughts were to be able to cut off the water heated supply to the garage in the future if it would save us on wood usage in the furnace in doing so.



If everything is plumbed in series (common in OWB setups), you won't be able to shut off any water - it's either the whole circuit flows, or it doesn't. You might be able to save some BTUs (and electricity) by turning the fan off while the water keeps flowing.


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## velvetfoot (Aug 2, 2017)

How about forgetting about heating the garage and put in a wood stove and heat that 1600 ft2 modular for 4 cords or less?   You'd have heat in case the power went out as well.


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## Highbeam (Aug 2, 2017)

velvetfoot said:


> How about forgetting about heating the garage and put in a wood stove and heat that 1600 ft2 modular for 4 cords or less?   You'd have heat in case the power went out as well.



Or just use the boiler for the garage if and when you need to. Run the stove in the house for primary heat.

I don't understand the fixation with wood boilers for houses that do not use hot water heat emitters like radiators or radiant slabs. 15 cords of wood per year and a very expensive boiler with a limited lifespan. You still have to tend the fire at least once a day just like I do with my woodstove in my 1700 SF home.


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## FarmLife (Aug 2, 2017)

Appreciate the suggestions, but for the time being, we are simply looking to utilize what came with the home to our best of ability.  15 cords may very well have been due to burning green wood, so it may not really be that much when we use dry this year.  Winter will tell us for sure either way.  The garage has a real wood burner that came with it and our insurance company says we need to pull it out or they'll drop the insurance.  I can imagine they'd potentially have similar issue using an indoor wood burner.  We're just trying to determine if we'll use less wood if we can somehow manage to not heat the garage.


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## maple1 (Aug 2, 2017)

I don't think the insurance issue is so much it being a wood burner, rather that it is a wood burner in a garage.


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## goosegunner (Aug 2, 2017)

15 cords is a tremendous amount of wood for a house and garage that size. 

1. As stated before use dry wood.

2. Don't load the thing full if you don't have to. Use small amounts of wood a couple times a day. Instead of filling the thing completely full to tend it once a day. Most times they will consume what you put in them if its needed or not.

3.  Buying 10-15 cords of dry wood is going to me really expensive way to heat a house that size. If you have propane consider using that instead and prepay now for the winters fuel.


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## hondaracer2oo4 (Aug 3, 2017)

Where are you located? That makes a big difference on heat needed per season. 

For a newer home with that sqft you are looking at a lot of wood. I would try to get a follow up of what the old home owners call a "cord". A real cord is 4x4x8. Dry wood is ussually around $300 per cord. You are looking at $4500 per year to heat. That is dumb. 

So I would confirm what a cord really is to the old homeowner. 

I used to have a conventional owb and it is best to mix green and dry to get longest burn times. You will get smoke but you have to do it to slow down the burn rate. 

As said before the most efficient burn times come from loading every 12 hours and only adding enough wood to get you 12 hours. 

Next make sure that the house is well air sealed and the attic has the correct amount of insulation and doesn't have gaps. 

Lastly check what you have for underground lines feeding the hot water to the house. If you have a "wrapped insulation" pipe product there is a good chance you have ground water in the lines sucking all the heat out of the lines before they make it to the house.


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## Bad LP (Aug 3, 2017)

maple1 said:


> I don't think the insurance issue is so much it being a wood burner, rather that it is a wood burner in a garage.



Ya, the insurance company as well as the code don't want wood fires in the garage next to gasoline for obvious reasons. 

My insurance company said nothing about having an indoor wood boiler in my basement.


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## Highbeam (Aug 3, 2017)

Bad LP said:


> Ya, the insurance company as well as the code don't want wood fires in the garage next to gasoline for obvious reasons.
> 
> My insurance company said nothing about having an indoor wood boiler in my basement.



This is a detached shop building that you can drive into. Not a garage (there is no real definition of garage). Some big insurers like State Farm prohibit solid fuel burners in outbuildings so that might be the problem here. I switched to another big insurer just so I could install a permitted woodstove in my detached shop with three 12x12 overhead doors.

The garage, for the sake of fire code and insurance, is an attached garage with no function other than holding cars.

Bottom line is that you need to be sure that you don't jeapordize your insurance. If they say no and you can't switch insurers then the answer is no.


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