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How to determine the size RMH you need

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Location: Western New York
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I was just curious if you have a design big enough to heat a 2 story 1,800 sq ft home? How do you determine what size RMH you need for space you are trying to heat?
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Cris McLouth : Basically you should view the Rocket Mass Heater RMH, as a space heater,well capable of keeping you and the core of your home comfortably warm!

It is difficult to retro-fit any heater into your home and expect that it will always meet your needs in every Case! Unless your house has a very open layout it is unlikely
that you will get much heat upstairs without overheating the down stairs, something you must work at to accomplish !

Here is a good video (the 1st one) For you to watch, it is a good realistic comparison ! ) )) ))) )))) ))))) :::-->

https://permies.com/t/25435/rocket-stoves/video-great-rocket-mass-heaters Highlight the Bold part and Right click to open in the address window,

or as a Google search !

The lady who lives here hosted a Ernie and Erica Wisner RMH Build during a long rainy weekend, basically getting the RMH custom built for her location nearly for free.

About the wood fly ash, yes she really is that kind of retentive personality that would save the ashes, and yes that looks about right ! Big AL

Sorry, often when I try and proof read, my mind tells me way it ''Thinks'' is there, it is corrected now ! Thank you David !
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Here is a link to the thread with the video Allen referenced- https://permies.com/t/25435/rocket-stoves/video-great-rocket-mass-heaters

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There are a couple of ways we often compare how big a heater is appropriate for a given space.
Square feet turns out not to be a great predictor, but it's the one fact about houses that most people know off the top of their heads, probably because it's how we sell them.

The heating load actually depends more on the surface areas of walls, ceilings, and especially on the insulation values of those materials. And of course on the climate.
Here is a calculator that lets you estimate the heating load for your own home, and incidentally may tell you a lot about key heat-loss areas to improve.

Another way is to roughly compare how much heat per month you'd get by comparing similar houses in similar climates that have used a given size of heater.
Heating about 3000 to 5000 sf in northern California, or 800 to 1500 SF on an inland mountain near the Canadian border, turns out to be a similar size of job, and we have used an 8" J-type heater successfully in both these situations.
Here is a website that lets you look up heating degree days, a measure of the total difference in heat to make up over the course of the year. Of course it doesn't tell you everything - like how long a cold snap might last, or whether you get warm days and cold nights or just damp clingy chill, but it's a good start for comparing someone else's situation when all you know is their house size and general location.

The short answer is, unless your climate is pretty mild, you'd probably want one of the larger heater sizes: an 8" J-type, or maybe a 6" or 8" batch-type (depends a bit on whether the materials you use let you burn the 6" batch type multiple times without overheating anything).

Erica W
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