Heat loss from added pole barn

A heat loss calculation for the barn would have, should have been your first step. You would need to do a heat loss calculation to size the heating plant properly.Do a heat loss calculation for the space you wish to heat. This will give you the information you need.

First off, is your forest eater an open to atmosphere system or closed?

Are the home and pole barn plumbed as one continuous loop or is the home set up as a separate heating loop or is there as second circulator for the pole barn?

Did you install a vapor barrier under the slab?

Did you insulate the slab and perimeter foundation of the pole barn??

What is the spacing of the of the pex in the concrete floor?

Did you keep the ends of the loops 6 inches away from the ends of the slab?

What is the ceiling height of the pole barn?

It all comes down to the amount of thermal mass you have. if you have a thin slab concrete slab you do not have a great deal of mass to store heat in. The heat transmitted through the pex to the slab will cool quickly because there is less and less heat delivered by your circulator or circulators that are pushing hot water to your home.

Short of filling your forest eater half full with standard fire brick to increase your thermal mass you will gain nothing.

Another option would be to change fuels by using a coal stoker boiler and filling the forest eater completely with standard fire brick and caping the stack to keep the heat in.

Alternate heating systems makes an outdoor coal stoker boiler that uses Pea Anthracite Coal for fuel

An electrician that works at a Montana coal mine eliminated his forest eater and placed an AHS S130 coal stoker boiler in its place building a shed to protect it and also store his coal out of the weather and he uses Montana mined Sub Bituminous Coal to heat his home and domestic hot water.

Not all pole barns are equal. I did radiant heat systems for a number of pole barn manufacturers in Missouri.

The key and challenging detail is the slab edge insulation, although the same issue as slab on grade framed homes.

We developed a Z flashing to cover the exposed edge of 2" foam used around the edge perimeter.

As some pole barns are built to the entry level price range, when using radiant there MUST be a good foam under slab detail used. 2" is the norm.

If the pole barn is insulated properly, the heatload should not be unlike a framed home.

I suspect in many areas pole barns are not held to the same building code requirements as homes. I've seen plenty insulated with just a 1" vinyl faced roll insulation in walls and roof, so very low R-value.

If you OWF is an open type you should have a heat exchanger between it and the backup boiler.

Are you adding corrosion inhibitors when you refill the OWF?

As noted, your wood and water consumption tells the story of the pole barns efficiency.

I looked online and couldn't find a BTU rating for that boiler, the best I could find is this page:

https://centralboiler.com/products/classic/cl-5036/

Which says it "Replaces up to 300 gallons of fuel oil per month." So that's 10 gallons per day. At 85% effiency a gallon of oil yields 96,000 BTU, ten gallons per day is 47,000 BTU/hr.

That doesn't seem like a lot of BTU for the amount of space you're heating.

You don't say how much wood you're burning, but on their website they have a calculator that shows a cord of red oak is equivalent to 139 gallons of oil. So burning at that top output would equate to a cord every 14 days, or every two weeks. If you're burning less than that your output is going to be less.

Missing from those OWF wood usage predictions are the quality of the wood, moisture content, and that it is burned at high, gasification temperatures.

So dry, aged hardwood would be the fuel for optimum performance.

Often wet, green, or too large of diameter wood is shoved in them. Unless wood is split down to 4 or 5" diameter the core will not air dry to a low moisture content

Studies years ago showed about 40 - 45% efficiencies in common OWF.

Some wood burners will swear that green or wet wood gives you more btus, than dried wood.

That is not quiet the case.

Diehard wood burners own and use a moisture meter to check the condition of their wood.

Some numbers, for crunching, here.

Output number vary based on the version of the 5036.The HDX shows 400,000, the NR at 250,000

I wonder what size oil gun the offer for the dual fuel?

o

"So burning at that top output would equate to a cord every 14 days, or every two weeks."

A cord is 4,000 lbs, give or take. Feeding the firebox three times a day would be 42 feedings in 14 days, or about 100 lbs per feeding if you're doing a cord every two weeks. Sounds about right.

Mowing the trench line in February is another good clue for leakage/BTU loss.