|
Post by ohioben on Feb 27, 2009 14:40:24 GMT -8
I want to build a rocket mass heater in a house with a wood floor. From the book I understand that I should have a layer of insulation under the combustion chamber, some air flow space below that, and some aluminum foil glued to the floor below that. My question is: What type of insulation should I use for this? I assume it needs to be a strong slab of something to support the weight of the stove. Also, does the heat-storage bench need to have the same insulation and air-space below it? Much gratitude to anyone who can help fill me in.
|
|
|
Post by Donkey on Feb 28, 2009 10:56:50 GMT -8
I use something strong like brick to build a void under the stove, then fill it with pearlite/clay mix. I know of no insulating material strong enough to hold up the works..
Yes, you will need to insulate under the bench too. At least under most of it. Depending on how long your bench is, down at the far end things should have cooled off enough to not need it anymore.
|
|
ernie
New Member
Posts: 32
|
Post by ernie on Mar 2, 2009 2:43:21 GMT -8
remember to shore up the floor where the stove is going. these things are heavy.
|
|
|
Post by ohioben on Mar 9, 2009 15:38:33 GMT -8
I'm having trouble visualizing building a void with bricks that is filled with insulation. Are you talking about building a container that the stove will rest on top of? If so, what would you use to cover the top of it and support the stove?
|
|
|
Post by Donkey on Mar 11, 2009 5:04:06 GMT -8
Lay 3 rows of bricks on edge.. Fill the space between the rows with fire proof insulation.. Lay bricks on top to cover.
The horizontal rows would need to be spaced so that the bricks covering them come tight to each other.. With 3 rows on edge, you can place over them 2 rows of brick laid flat...
Err.. I could post an image if you wish, though it will take a couple days.. I'm suddenly SUPER busy, which is good, but allows little time for stove stuff at the moment.
|
|
|
Post by jgreen on Mar 11, 2009 11:55:28 GMT -8
I'll write something about my experience this year, building my first rocket mass heater. I had success (so far... rocket has been in regular use this winter) using a perlite/portland cement mixture as an insulating material under the stove I built in a mobile home this year. The combustion unit sits on a plywood subfloor and I poured a "slab" about 8 or 9 inches thick, using something like 1 part cement to 8 parts perlite (I forget the exact ratio now). The bottom layer of firebricks are layed on top of that and then the combustion unit is built as per the rocket mass heaters book. The brickwork was re-sized to work with a 7" flue pipe, and the stove burns pretty hot with no issues so far.
I have pictures of the construction, including some good ones of this insulating slab but I only use the internet once a week on wednesdays, and don't have my camera with me today. If anyone is interested or thinks it might help them see what to do/what not to do, I will upload pictures and post a link next week.
|
|
|
Post by johnjmw on Mar 12, 2009 3:26:25 GMT -8
jgreen, the 8:1 Perlite Portland mix, was that measured by volume? I've been thinking of a similar mix for insulating the burn tunnel after placing the fire bricks in place. Either that or using just enough clay to hold the perlite. The property where I am going to be building has lots of clay in areas close to the surface. John
|
|
|
Post by jgreen on Mar 16, 2009 13:07:23 GMT -8
johnjmw-
The 8-1 mix was indeed by volume. I used portland cement to ensure the strength required to hold the weight of the combustion unit... however clay slip is perfectly suitable (as you suspected) for holding the perlite together when having a high compressive strength isn't necessary (and it may be possible to make a clay slip/perlite mix that could support a lot of weight without crumbling, I've just never tested that.)
When insulating around my burn tunnel, I just built up a "retaining wall" of cob around the area to be insulated and filled the gap with pure loose perlite (no clay or cement). I think this gives the perlite a slighter better insulative ability, at the expense of having a larger, less compact stove unit (but more thermal mass).
|
|
|
Post by Donkey on Mar 17, 2009 8:08:31 GMT -8
Loose pearlite probably does provide higher insulative properties.. However, I've noticed that it has a way of finding ANY crack or hole, no matter how small and eventually end up blowing around in the works somehow.. The stuff is rather fiendish that way.
|
|
|
Post by johnjmw on Mar 26, 2009 10:00:05 GMT -8
On the burn tunnel, I was thinking about not "cementing" the bricks together with anything, just dry stacking. Then using the insulating mix around that. I know cementing is not what I'd do, but didn't know what to call the clay slip that could be used. The slip would keep the perlite from doing any settling. Having the bricks dry stacked tightly would allow them to not cause as much stress fractures, at least that was the idea. John
|
|
|
Post by ohioben on Apr 6, 2009 16:52:26 GMT -8
Donkey - Yeah I can picture three rows of bricks with insulation in between and two rows of bricks covering it. My only concern would be if the bricks on edge would act as a heat bridge to the floor, making the insulation ineffective. But if this has worked for you, maybe that's not the case.
Pouring a slab of the 8-1 perlite/cement mix seems like a viable option, too.
jgreen - If you get a chance to post pictures, I would like to see them.
|
|
|
Post by doceanboy on Jul 10, 2017 11:08:10 GMT -8
I like the idea of putting 8 or 9 inches slab underneath the stove of perlite and concrete, but what do you think of the idea of pudding 3 or more 4inch pipes In the slab so that air can pass through them? I'm thinking it would cut down on the weight and you may be able to recuperate some of the Heat.
|
|
|
Post by Donkey on Jul 20, 2017 20:38:13 GMT -8
Yeah.. Actually you're right, air channels all the way under the stove are better. Heat can get through the insulation and concentrate!! I was totally wrong back then. You can insulate under, but you need air space that can vent away under that! So now the recommendation is to use the same trick, bricks on edge with bridge bricks or something similar to create air channels under the combustion unit and perhaps also some of the bench/bell, depending.
|
|