First step to new boiler: heat load calcs

Hi All, I've read a lot on this forum about the gasification boilers and it looks like an ideal heating solution for me. We have been supplementing our oil furnace with a old fireplace insert the last two winters and it has worked out very well. We live on 15 acres of dense forest and have been cutting walking trails and a small area for a meadow, as such I have more wood than I could ever hope to burn.

The reasons I want to add a wood boiler and use it instead of the current insert are

• we have a newborn and his main play area is the same room the fireplace is currently, would like to move the source of heat and smoke out of the living area
• Wife would like the bark and ash to stay out of the house
• Would like to add heat to the garage and to the family room off the back of the house (they are both heated by electric currently and thus not used often)

Instead of using a set of analytical equations I hooked a thermocouple to the furnace and datalogged the total runtime over a 10 day span ( it has been from -3 to 40F pretty typical for SE mass). The furnace has ran between 4.6 and 5.2 hours per day in that time, with a 0.65 gph nozzle that works out to ~ 455,000 BTU/day or 133kWh. Does this seem correct for a ~1650 square foot colonial that is well insulated?

The Eko 25 seems like a good fit, as we are not replacing our current heating system, only adding the wood in parallel. Would also like to add radiant to the family room and a modine type water to air heater in the garage for occasional use. The garage is very well insulated as well and the current 3kW electric heater does a decent job making it comfortable in there.

At some point it makes sense to add a sidearm heat exchanger to the input to the GE heat pump water heater, but I don't want to get ahead of myself yet!

Thoughts? Feedback?

hobbyheater said:

Welcome to Hearth !
The only issue that I see is the boiler in the garage .I think the boiler would have to in its own room in the garage with a separate door to the outside .

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Is that a building code?

jeffesonm said:

Yes I believe that is building code... they figure garages have gasoline, oil, vehicles, etc. so no source of combustion. Some build a wall to section off a part of the garage.

Were you also burning the insert during the time you were measuring furnace usage?

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No the insert was off the entire time I was measuring burner run time. Pulled it out for cleaning and new gaskets.

I will have to review the code, and make room in either the basement or shed.

Thanks!

maple1 said:

Is your existing system hot air or hot water? Assuming hot air but not sure. So, you say run 'parallel' - but not sure what you mean there. Do you mean putting a HX in your furnace plenum & using the ducts for distribution? I think that would be the common thing done with exisiting forced air.

And do you have any room at all for storage? With 1650 sq.ft., and wanting to expand heating to include a garage & extra room off the back (I think that's what you mean) - I would be tempted to move up to a 35-40kw boiler. But maybe not if you can't or don't do storage.

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Yes, I have a oil furnace with forced hot air. The plan was to put a HX in the duct, directly below the current AC HX. http://www.outdoorfurnacesupply.com/water-to-air-heat-exchangers/hwc-18x17.html

For hot water I was planning on using a small HX in parallel to the GE heat pump we have now http://www.outdoorfurnacesupply.com/side-arm-heat-exchangers/she-sweat.html
http://www.lowes.com/pd_386797-83-GEH50DEEDSR_0__?productId=3664968

My plan was to do ~250 gallons or so of storage in the basement, since that is were the existing furnace and water heater is. Most likely a 250 gallon propane tank or something similar. I am very limited on space in the basement because it is partially finished.

Overall my main goal is to have the existing heating systems remain unaffected and automatically take over is the wood boiler temperature drops. I am also ok with the current systems running a bit every day, if I can reduce the oil and electric usage by ~70%, and have heat in the garage/family rooms when needed, I would be very happy!

jeffesonm said:

19k btu/hr sounds reasonable for a well insulated house of that size.

Benefits of a shed install are keeping all the wood/smoke/mess outside, and presumably less moving of firewood. Drawbacks are $ for underground lines, having to go outside to feed your boiler, some sort of plan to make sure things don't freeze if your power goes out, and any incidental heat loss is actually lost to the great outdoors.

Basement means you have to move ~75 lbs of firewood/day and cleanup any associated mess. Also any smoke spillage goes into your basement. On the plus side, any heat loss at least warms your basement, and it will never get cold enough to freeze down there.

Also give some thought to how you might move a ~1500 lb boiler and potentially big, equally heavy storage tanks into your basement.

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Putting the boiler in the garage made alot of sense to me but that seems to be out due to code so the shed is a better idea. I have a 16'x24' shed near the wood pile, it is a 35' run to the garage.

It is not insulated, but running an antifreeze mix I should be ok if we go away on vacation or the fire goes out for several days?

I have an 8' overhead door in the shed, I could bring in one pallet at a time on the skidsteer, seems like the best way to go.

PassionForFire&Water said:

I would start with your annual oil consumption in gallons.
Your location has a certain number of heating degree days (HDD).
You look up the min/max/average HDD for Dec/Jan/Feb, the coldest months.
With this you can find your max BTU/hr heat loss of your building.
Look up a couple of my previous postings, there are some examples.
As an engineer you should be able to reverse engineer my spreadsheet

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Is this going to give a difference answer than the data logging I already did in terms of sizing a boiler?