Simple rmh for a greenhouse

I would like to build a simple rocket mass
heater for an existing 16’ x 20’ greenhouse.
I would rather it be outside, with the heat
piped in. I live in west Tennessee. I’m new
at this and would appreciate any advice.

Hi Kevin,   No personal experience to share but link to info on the subject: Greenhouses forum

Hi Kevin : Welcome to permies!

Do you have a copy of the RMH Builders Guide, by Ernie & Erica Wisner ? It is the go to book of any aspiring rmh builder and will answer a lot of your questions. It is readily available on amazon or directly from them.

Are you wanting to extend your growing season ? Or are you wanting to heat your greenhouse thru the winter ?


We have a 12 x 20 greenhouse / artist studio here in northern Montana. We keep in warm all winter long on less than 5 cord of wood.  Our RMH is indoors , its the only way we can have no fire all night long at zero or less and a room temp of 40 next morning... in a plastic greenhouse...

Thanks for the response.  I've ordered the book.

My main objective is to keep some patio plants alive through the winter.  I would also like to grow some vegatables and other plants during this time.  I also plan on starting all of my garden plants in the greenhouse, from seeds.

Winters here in west Tennessee aren't very harsh (daytime temps usually 40's - 50's, nighttime temps usually 20's - 40's.  The greenhouse stays plenty warm during the day but cools really quickly at night.  I would like to be able to divert the heat from the
greenhouse during the day.

Hi Kevin;
That's great you have the builders guide ordered , its considered the builders bible. Reading it will give you a much better understanding of the terms and design in rmh construction.
Having the rmh inside is really the way to do this.  If you don't have the stove lit your only extra room heat is coming off the mass. On average a mass might be 100 F imagine a 90-100 degree rock sitting inside your greenhouse all night, by morning most might be 60-70 degrees ... That's not enough to super heat the room during daylight hours.
All greenhouses need ventilation of some kind no matter if they have a stove or not. In the late afternoon you would want to fire up the RMH , dependent on temps is when you start and how long you burn. It will be a learning curve for you. Further complicated by a new build needing to dry out and heat up all the way, that takes time... the dryness of your wood is another factor in how long it takes to dry and in how well it burns.
We used our mass to set start trays on, to keep their feet warm, potted plants same thing.  It works great ! It goes below zero here in the winter and our plastic greenhouse has no fire all night long and next morning it will be 40 degrees ...  

Thanks for the advise.  It's greatly appreciated.  
I look forward to receiving the book.  

I would think that the main heat from a rocket mass heater would be in the immediate mass surrounding the burn chamber and riser.  If you have the burn chamber outside the greenhouse, that would be really inefficient since you're then relying on hot air to mass heat transfer which is difficult.