Outdoor pellet boiler question

seymour · Mar 17, 2014

I am in the process of buying a maxim 250 outdoor pellet boiler and they are equiped with two seperate output/input line. so one will go via thermopex 75' underground to my house while the other was going to be used to heat my garage which houses the boiler. the problem is I have an overhead rad/fan heater in the garage that i currently heat with my pressurized wood boiler (eko40). the rad is located higher than the boiler, Will the water just pour out the fill cap? I know they are not technically pressure vessles but there will only be the weight of watever water is in that rad (maybe 5-10 gallons at the most) essentially I'm trying to eliminate the hassle of another water-water exchanger and a second pump.
My house is pretty well insulated and is about 2800 sq feet with lots of south facing windows but my garage is poorly insulated and 24x38 so I would really like to be able to use the garage to "dump" some of the excess heat that the 250k btu boiler can put out therefore reduceing cycle times. aka heat garage warmer when house is warm and cooler when outside temp is cold and house is in need.
please pitch in if you own a maxim pellet boiler as well, any info or advice, thanks

PassionForFire&Water · Mar 17, 2014

I think you should determine your heat load first.
How did you heat your house before?
With the wood boiler?
How many cords did you use?
21,000,000 btu per cord is a good number to start with
Did you use water storage with your wood boiler?
250,000 is a big output

harttj · Mar 18, 2014

seymour said:
I am in the process of buying a maxim 250 outdoor pellet boiler and they are equiped with two seperate output/input line. so one will go via thermopex 75' underground to my house while the other was going to be used to heat my garage which houses the boiler. the problem is I have an overhead rad/fan heater in the garage that i currently heat with my pressurized wood boiler (eko40). the rad is located higher than the boiler, Will the water just pour out the fill cap? I know they are not technically pressure vessles but there will only be the weight of watever water is in that rad (maybe 5-10 gallons at the most) essentially I'm trying to eliminate the hassle of another water-water exchanger and a second pump.
My house is pretty well insulated and is about 2800 sq feet with lots of south facing windows but my garage is poorly insulated and 24x38 so I would really like to be able to use the garage to "dump" some of the excess heat that the 250k btu boiler can put out therefore reduceing cycle times. aka heat garage warmer when house is warm and cooler when outside temp is cold and house is in need.
please pitch in if you own a maxim pellet boiler as well, any info or advice, thanks

I don't think you will want to "dump" any of that energy. This is a pellet boiler that will only feed what is needed. It has 3 steps, idle, normal and high. Each can be set differently.

In theory you shouldn't need another heat exchanger. The company I bought mine from says it works fine as long as there are no leaks to allow air in. Think of a straw with your finger over it. I chose to install heat exchanger.

I hope you never have to run at 250 k for any length of time. I had to run at 100k during the polar vortex for over 48 hrs and sucked down some serious fuel.

Tim

PassionForFire&Water · Mar 18, 2014

250,000 BTU/hr is close to 32 Lbs of wood pellets per hour (@8,000 BTU/Lb of wood pellets) !!!

or 768 Lbs per 24 hours (19 bags of 40 Lbs) !!!

heaterman · Mar 18, 2014

PassionForFire&Water said:
250,000 BTU/hr is close to 32 Lbs of wood pellets per hour (@8,000 BTU/Lb of wood pellets)
or 768 Lbs per 24 hours (19 bags of 40 Lbs)

You have to remember the net efficiency of those things........

seymour · Mar 19, 2014

PassionForFire&Water said:
I think you should determine your heat load first.
How did you heat your house before?
With the wood boiler?
How many cords did you use?
21,000,000 btu per cord is a good number to start with
Did you use water storage with your wood boiler?
250,000 is a big output

there are a lot of unknowns in the house so heat load calc is difficult
yes currently heating with wood gasser
used about 20 cord this year (local average is about 20-25cord)
currently using 500 gal pressurised storage
maxim only available in one size.
hope this clarifies, thanks

seymour · Mar 19, 2014

PassionForFire&Water said:
250,000 BTU/hr is close to 32 Lbs of wood pellets per hour (@8,000 BTU/Lb of wood pellets)
or 768 Lbs per 24 hours (19 bags of 40 Lbs)

there is no anticipation of running anywhere near 250k the current boiler (eko40) puts out 136k in a perfect world and it does fine as long as its fed. the problem with it is making two fires a day in the -40* days and it demanding extremely dry hardwood (95% softwood around here)

jebatty · Mar 19, 2014

I assume by stating that the Eko is "demanding extremely dry hardwood" you mean that the hardwood gives you longer, hotter burns per load than dry softwoods (more btu/lb). I burn only soft wood, pine and aspen, in my Tarm Solo Plus 40 and that has worked very well since 2007.

Is your 500 gal storage in the garage? Are you going to use that with the pellet boiler? The storage would be an excellent heat dump.

maple1 · Mar 19, 2014

seymour said:
there are a lot of unknowns in the house so heat load calc is difficult
yes currently heating with wood gasser
used about 20 cord this year (local average is about 20-25cord)
currently using 500 gal pressurised storage
maxim only available in one size.
hope this clarifies, thanks

That must be face cords?

I think if I was going to move to pellets it would be an indoor pellet boiler, in my basement. The thought of burning pellets in an outdoor boiler gives me the heeby jeebies - I would think you would be looking at a very high fuel bill. Before taking that unknown plunge I would do my best to come up with a heat load calc no matter the difficulties - but it would likely be an underestimation if you then try to factor in the Outdoor Boiler part. Then there's the local pellet supply situation - lots of areas had unforeseen supply & pricing problems this harsh winter.

EDIT: BTW, 500 gallons of storage is kind of limiting your Ekos potential. Any thoughts on adding more storage? And I don't think I would term it's wood dryness needed 'extreme' - IMO anything that burns wood should be burning it at the same dryness.

harttj · Mar 19, 2014

jebatty said:
I assume by stating that the Eko is "demanding extremely dry hardwood" you mean that the hardwood gives you longer, hotter burns per load than dry softwoods (more btu/lb). I burn only soft wood, pine and aspen, in my Tarm Solo Plus 40 and that has worked very well since 2007.

Is your 500 gal storage in the garage? Are you going to use that with the pellet boiler? The storage would be an excellent heat dump.

Storage not needed and not desired with a pellet boiler. Only more heat loss.

PassionForFire&Water · Mar 19, 2014

harttj said:
Storage not needed and not desired with a pellet boiler. Only more heat loss.

In my opinion this is to general of a statement.

For a modulating pellet boiler like a Windhager BioWIN I agree.

For the Maxim (It has 3 steps, idle, normal and high) I definitely would advise as much thermal storage as possible and let it fire at the high as long as possible.

Fred61 · Mar 19, 2014

If you're burning 20 to 25 cord of wood you're building more than two fires per day in an Eko 40. I'd say you're stuffing wood in it every hour.

maple1 · Mar 19, 2014

Fred61 said:
If you're burning 20 to 25 cord of wood you're building more than two fires per day in an Eko 40. I'd say you're stuffing wood in it every hour.

Agree - which is where my face cord question came from.

heaterman · Mar 20, 2014

harttj said:
Storage not needed and not desired with a pellet boiler. Only more heat loss.

A lot depends on the type of system it is connected to.
High mass Radiant floor, definitely not needed.
Low mass radiant, depends on the btu load per zone.
Near zero mass system with instant on load capability ala a hot water coil in the plenum of a furnace....I would say you definitely need a buffer tank or low volume (60-100 gallon) storage tank.
Otherwise you will have an undesirable ratio of start cycles per hour of operation.

harttj · Mar 20, 2014

heaterman said:
A lot depends on the type of system it is connected to.
High mass Radiant floor, definitely not needed.
Low mass radiant, depends on the btu load per zone.
Near zero mass system with instant on load capability ala a hot water coil in the plenum of a furnace....I would say you definitely need a buffer tank or low volume (60-100 gallon) storage tank.
Otherwise you will have an undesirable ratio of start cycles per hour of operation.

The boiler in question has 100 gallon built in capacity.

seymour · Mar 20, 2014

yes the 20-25 cords are face cord. I am burning a mix of poplar and spruce with a bit of birch mixed in. I make one fire in the morning and one load before bed, we started our heating season this year on Oct 15 and the forecast for the third of april is 14*F we have had weeks of -40* (not days, weeks!) so ya pretty easy to burn through 20-25 cord. alot of folks up here are into 30-35 cords, and there is a guy near me heating a 6000 sq ft house and a shop and he was at 172 cords last i talked to him. (yes one hundred and seventy two) anyway I was not planning on using the 500 gal tank with them pellet boiler but rather keeping my eye out for a smaller 200 gal upright tank that would take up less room so i could put it in the basement. the boiler will indeed be located in the garage but it is a model that is rated for outdoors and the garage will be heated, should be no additional cost over an in the basement model. As far as heating calcs go, I have a collection of cast iron rads throughout the house and infloor heat (wood floor) on the main level. The stove puts out 250k btu so i'm not worried about being undersized and they only make one model so I can't go smaller. as far as fuel usage as best as i can figure by comparing others in my area with the same stoves, I should burn between 7-9 ton of pellets a year which is great because I buy them direct from the plant in a gravity grain wagon for $125 / ton. worst case I'm talking $1200/yr for heat which is alot better than my dads propane bill at $1000/month six months a year! anyway all the replies have been greatly appreciated and keep them coming, if you want any more details or have any more tips just let me know. thanks

maple1 · Mar 20, 2014

Is your insurance company OK with an outdoor boiler installed indoors?

seymour · Mar 20, 2014

yes they have looked over the specs on the boiler and as it is a "zero clearance appliance" they are fine, also no living space attached to garage was a condition, garage is located 50 feet away from house.

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