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Mass Heater Question.

 
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We need to heat 65,000 cubic feet over three stories. What size rocket mass heater should we build (height, width and length) should we build? The Mass Heater will be on the ground floor and the heat will distributed throughout the building through a hood attached to the duct work.

Thanks!
 
pollinator
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You need to give us more information before we can help you. If the volume you want to heat is in Florida, a much smaller RMH is needed than one for the same volume in Minnesota. What is your current system and how many BTUs does it produce during a heating season?
 
Tj Brooks
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We don't have a system designed yet, but are planning to build a home off the grid in the Ark. In the Ozarks. We overestimated somewhat the CUBIC footage as we haven't done the math to get an exact measurement. ( the top floor ceiling peaks at 18' and slopes downward to meet the floor. Bldg is three floors and approx. 40' x 44' external dimensions.
 
John Elliott
pollinator
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A-ha, making progress. I can look on wunderground.com for Ft. Smith AR and see that January of 2013 recorded a total of 671 degree days (base 65F). Now we have to figure out a correspondence between degree days and how many BTUs are required to keep the building comfortable. Since this is a new construction, you have control over how well insulated you are going to make it, so it make take a lot less BTUs to be comfortable than the uninsulated old clapboard house down the road.

Now's the time to check out what freebie heat load calculators there are online. Here is one that I found with a little Googling, see if that will help you out. Once you know how many BTUs per hour the building will lose, then you can zero in on how big your RMH needs to be. For instance, if you get a number like 30,000 BTU/hr, you know that your RMH will need to be able to eat about 5~6 pounds of wood per hour to keep up.
 
Tj Brooks
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Thank you. We can estimate everything except the Infiltration @ 0.4 ACH volume (cu. ft.). Any idea on how to estimate this? We plan to build a well insulated, tight home. 12" in sidewalls and 20" in the attic of spray foam insulation.

Thanks.
 
John Elliott
pollinator
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Try total window area in square feet divided by 4. Then see how much it changes the calculated number when you increase or decrease it by 50%. When I use values for my house, it doesn't seem too sensitive to this number.
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