greenhouse rocket stove questions

We are considering building a lean to greenhouse this year. It will be 8 ft. wide and 32 ft. long. I was interested in putting a rocket stove in it to heat it at nights in the winter. It will be built from a polycarbonate roof and used sliding glass doors for the walls. I am unsure how hot these stoves get and don't want it to break the glass or melt the plastic. I could build a small room to put this in if necessary with wood or metal walls and just put ductwork into the rest of the greenhouse. I understand that I can not use concrete as high temps with cause it to explode. I also understand rocks can do the same thing. We don't have clay in our area, so one of my questions is: What can I use to create a mass that will hold the heat that won't explode? Our ground is mostly sand here. My son's room is right next to where we need to build the greenhouse so want it to be very safe. How do I know how big of a rocket stove to make?
How long will the barrel and ductwork last? Do you have to replace it yearly? How hot will it get? How much of a fire hazzard are they? How long to you have to burn the fire to keep the greenhouse heated all night? I like to have all the facts before making a decision. Thank you so much for any help that can be provided. I appreciate any ideas. Thank you so much.
veggiegal

Well you have a few ways to go you can bury it in a raised bed (my personal favorite) you could leave the ducting uncovered and just heat the air (least efficient) or you could bury it in the floor of the green house (not to bad if it is isolated from the surrounding soil. the raised bed is probably the best as it gives you a nice thermal mass and plantings at a workable height.

the stove will not get hot enough to blow up rocks in most cases (dont put them on the barrel top). the ducting will last for a few years (one big reason to use cob is that it makes ducting for you and the ducting doesn't matter.) and the barrels are going on 15 years of constant use and counting. If the stove is built well you wont need to put the feed and barrel in another room but i would do this so i could ensure that didnt have any smoke problems with my plants.(Especially if i was new to RMH's)

the temps should not melt the plastic or crack the glass with a bit of space between the hot parts and the materials. the only place to worry is directly above the barrel and this is simply a need for a bit of space. (or a bit of plywood) I would look at the leantoo design and make my back wall a good thermal barrier (we used straw bale and cob for ours on the home stead.) the only problem we had was the roof had a leak and the bales on the top got a bit moldy; just build a better roof than ours and you have it in the bag.

remember the more thermal mass you have the better a green house works for winter growing. isolate the inside floor from the outside soil to keep the heat from escaping to the out side soils. a cover for winter (visqeen works well) to give you a bit of protection and another thermal barrier that can be rolled back for the best part of the day will make a nice snug green house at night. I might add make a space in the green house for sitting and relaxing so folks dont get he idea that its all work and no play.

Hi Cheryl : I created the forum thread 'Rocket stoves in greenhouses' to give new members self-identifed in this group their own forum thread 'Rocket stoves in greenhouses' Check in Check often, Allen L.