RMH built in basement. Will it radiate upstairs?

Hello! I'm new to Permies. I spent over 3500 dollars on propane last winter so I decided to heat with wood for this next year. I have been wanting to build a RMH for the efficiency and I have an existing chimney hook up in my walk out basement (where an old wood stove was years ago). The house is a total of 1300 square foot and the walk out basement covers 3/4 of the main floor above. I'm wanting to build the RMH and allow the radiant heat to rise into the upstairs through floor vents just like the old school wood stoves in old farm houses. I have enough room to build a large mass but I'm concerned if the RMH will produce enough heat for the square footage. Does anyone have any thoughts? What's the largest square foot house that RMH have heated? Anyone built one in a basement for this purpose? And thoughts will be much appreciated! Thanks

Hi Jason,   Welcome to Permies.  Installing a rocket mass heater (rmh) in a basement is a commonly asked question. The answer is usually "not recommended" because its the type of heater that requires attention. (Less so if you were to install a batch box heater but thats something usually for a second build).  
In other words, unless you spend quite a bit of time down there already, its gonna get old real fast making the journey up and down the stairs to feed the fire.
Also, being so low in the building, some issues with negative pressure may cause smoke to travel in reverse thinking that your house is a chimney instead!
All of this and more can be found in the Rocket Mass Heater Builders Guide and if you do a search in this forum, there has been conversations about this also.
For sure you'd be looking at making an 8" rmh.

This is a short video of the layout of the house. Only about a 3rd of the basement is inside a hill, leaving 2/3rds exposed. So it's not a true basement.

I don’t really know much about house installations but I think you might be better off looking into batch box design and bell heat distribution.
That design will possibly be more suitable but I think you will need to do extensive revision.

RMHs provide a lot of heating through conduction and radiation, so if you are in the same space you get the best results. Convection also happens but to a lesser extent. My main experience with RMHs was spending about 10 days at Cob Cottage where the Myrtle (library) was running the RMH each night around dinner time for say 40 minutes, and that was it. In the morning it might have been 38-40F degrees per the outdoor thermometer, but you'd step inside Myrtle for breakfast and this wall of heat would greet you at the door.

That space was essentially one room, so most of that could have been radiant heat. But as several of us were moving around, you never felt like you do near a fire, where the side facing away is cold. The Myrtle is a totally cob structure, so that big thermal mass would absorb RMH radiant heat during the evening and solar radiant heat during the day through passive solar design. So perhaps that balanced the heat we felt in the morning. The day would warm up to 50-55 but the house was always very comfortable. All that said, heating the basement up nice and toasty would certainly happen, but if the foundation isn't insulated on the outside then the walls would be a heat sink and rob some/a lot of the heat. Meanwhile the wooden floor joists and framing aren't going to conduct as much heat up, and some convective heat can travel up the stairwell but I doubt it would be enough for the rest of the house.

If you can use waste wood to run it, then the RMH would probably lower your heating bill, but probably not eliminate it.

Alex's one

http://donkey32.proboards.com/thread/1973/8-215mm-double-bells-built?page=6

Worth reading the whole thread.


Mine, heating the two floors, with barely any insulation, 5000ft elevation, in the french alps.

https://permies.com/t/44806/Cobbling-workshop-heater

635m3

Hey Jason Speaks, just wondering if you followed through with your idea? I'm thinking of doing the same sort of idea too

so i have zero experience with rmh's, but i would think that as your house is currently, it would do a pretty poor job. but it does make you wonder where does all the heat go? it goes somewhere.

on the original wood stove or coal burner in the basement, it worked by heating the chimney mass, and you got radiant heat off of it. you will be putting out (in comparison) fairly cool air into the chimney. on a traditional gas furnace, it heats up an exchanger that heats the air quickly and blows it all around. Some people that have wood stoves put high returns above the stove to their furnace and use only the electricity of the furnace's fan,

in old lathe and plaster buildings you sometimes see old school vents that were simply large, fancy, and decorated holes in the floor that let the hot air rise from the room with the hearth. Your house seems to be a modern one with drywall and mudded up joints etc. getting the heat to raise would be easy in a 1600's cabin where the flooring was optional (probably non existent) and subflooring wasn't tongue and grooved, but just boards nailed down with gaps in between.

The question is, could one or many of these ideas be utilized in your basement rmh? Perhaps designing the mass to be like a gas furnace and taking the hot air off of it. essentially having an intake return to your furnace and letting it blow through your forced air. if it wasn't through some kind of heat exchanger within the cob, i don't think directly venting to a furnace intake would be a good idea unless it was only while it was burning efficiently. sounds like a big no no to me without a heat exchanger. In my mind this would be a bunch of vent pipes that were long enough to gather heat through your mass, possibly also from around the riser, and then routed to your furnace. heated air doesn't passively go downwards, but with a fan sucking it, it would.

the heat that would radiate and keep your basement cozy would be lost to your basement walls and the earth or air outside of them, and since they are not cob connected to the other floors, you would not get much if any heat to the upstairs. But if you could get the heat to directly raise to various areas above by finding open joists and cutting holes in your floor, it might be possible. Since the layout of your house isn't just one big room upstairs, and the basement ceiling isn't angled to let the hot air focus anywhere, this would also be a limited idea. in my old house, it was designed for a coal burner in the basement, and it now has a gas furnace. When we moved in, there was one vent to heat 3 (2 when we moved in) bedrooms upstairs and it was in the hallway. we were cold even with the door open and most of the vents closed on the first floor. At first i installed vent holes in a few areas on the first floor and installed inline fans that were controlled by a thermostat to the second floor bedroom vents. Menards has 6 in and 8 in inlines, but you have to replace the wires on them to be hardwired from an outlet. anyways, it wasn't passive, but it worked. i eventually removed the hallway vent and re-routed it to hook up with the pipes i installed and removed this system, but it worked. i wanted the house to make sense for the next owner and for the vent to be more efficient.


Anyways, you could do all of these, but your best bet would still be having it in the same space. That would involved building a platform all the way from your basement to the first floor. not a simple or cheap endeavor.

The description of your home is very close to my own. I've settled on finding an "add-on wood furnace" to sit in the basement next to my normal furnace. These wood furnaces pipe heat into your existing duct system to flow throughout your house. Basically you load it with wood and when it goes cold your normal furnace kicks on. I'm going to use the existing chimney just like you mentioned.
I considered RMH and masonry heaters, but learned that these only work well if you're in the same room. So I'm settling on carting wood in through the walk-out basement door and loading up the fire box once or twice a day.  

I have an app that shows how much power I'm using to heat my house. You could just add up all the kWh of all the electric heaters you are using. That then gives you a figure of how many BTUs you need to burn to heat your house from using wood. But it's not going to be very efficient if you build a radiant heater in the basement and rely on convection to take heat upstairs. Why can't you put the rmh upstairs?

Or, have a batch box, and a really tall highly insulated riser that penetrates the floor and ends in a stratification chamber on the first floor that stores all the heat in brick or stones?

http://donkey32.proboards.com/thread/1973/8-215mm-double-bells-built?page=4

https://permies.com/t/44806/Cobbling-workshop-heater  

A Rocket mass heater will not work in a basement well because as others have said, it works primarily by radiating heat...known as radiant heat.

Radiant heat works by heating the CONTENTS in the room, and then those contents give off heat that help heat the air. There is a ton of benefits to that, and one benefit that is both good and bad is, that radiant heat does not go above 8 vertical feet. In a basement setting, this is kind of bad because while it will heat your basement, it will not travel to the upstairs. But in certain situations, like a home with high ceilings, or a home with a cathedral ceiling, it means you only direct-heat the areas where a person lives and moves, so it can really help on energy bills.

Travis, have you tried it?

Satamax Antone wrote:Travis, have you tried it?

Sort of, not with a Rocket Mass Heater, but rather with a woodstove, and if a woodstove in the basement will not heat up my home, then I am sure a Rocket Mass Heater certainly won't.

Travis Johnson wrote:

Satamax Antone wrote:Travis, have you tried it?

Sort of, not with a Rocket Mass Heater, but rather with a woodstove, and if a woodstove in the basement will not heat up my home, then I am sure a Rocket Mass Heater certainly won't.

Well, depends how you implement it.

My rocket heats the whole workshop, at ground floor, and by convection, heats upstairs. Also, heats the lounge and bathroom va conduction. the back wall of the bell transmitting heat upstairs. I live in the alps, at 5000ft elevation. Not much insulation. And i have never been cold. Rather too hot. In 4 years of use.

Why we say, rockets in a bassement don't work, is more due to drafting problems than anything else. Best way to do it well in a bassement, is to have just the "engine" down there, and leave the room cold. With a batch. Not a J tube. And have the riser go through the floor, with no barrel, and fill bells upstairs.

And avoid by all means all leaks between the basement, and the house. To counteract the whole house stack effect. In my case the house is fairly drafty, but i have a nice chimney. And it works.

https://en.wikipedia.org/wiki/Stack_effect

Alex's solution also works.

To run a rocket in a bassement, a window has to be open. Or have a proper air intake. No "blind bassement" rocket will work.

So the way my house is set up. I have one propane heater in the basement, like you would find in a small trailer or apartment. I have a furnace in the attic, that pushes blown air from the ceiling. Both really dumb designs. The last 2 months I've spent allot of time re-insulating the basement and blowing in insulation in the attic (my mind blew when I saw how poorly the house was insulated). So I'm stuck with 2 heaters using propane. I've come up with an idea. I'm going to build a RMH where I was thinking. My family room will be down stairs because it's cool in the summer, and now will be warmer in the winter. Upstairs will be supplemented by the bigger furnace. So I have started the build, so I guess I'll be a guinea pig to see what the max it is going to affect my house over all. I will be providing pictures as I build the process. Also on of the things I'm doing is opening up the basement more for heat flow. RMH or regular wood stove, It needs to be done. If the RMH replaces the downstairs heater, and gives a little to the upstairs, then it should cut my heating bills in half. In the cold of winter last year, the heater downstairs would barely shut off.

The progress of the RMH. I started setting the block and did a dry fit of the J-tube. Hoping to have the heater and first layer of cobb in by next weekend. Also, does anyone know of the best place to buy Perlite? I want to use it to insulate under the heater. Thanks!

I bought my Perlite at a growers supply Co.  110L bag.  You can get it online also at amazon.

Started setting the burn chamber. For only dry fitting it twice, it is all within 1/8 in. Also burned the paint of the barrels today. So I would like to get the manifold cut and set tomorrow and finish the riser.

It looks like you have the burn tunnel about 7 1/2" wide, but only 4 1/2" tall. That is not a good idea - the cross section should stay relatively constant throughout the core. If the burn tunnel is smallest, you will not likely make a hazard, but you will distinctly reduce the heating capacity of your system.

I would strongly advise pulling the top layer and raising it now, before you do too much more.

Thanks for the concern. The tunnel is 7in. I have one laying flat and the other is on end. End up equaling a light 7in. It's 7.5 x 7 all the way through. I'm working on the manifold right now. Hopefully will have it on in a day or two. Then working on the exhaust to the chimney. Would love to fire it up sometime next week to check the draft.

Ah, good. So that's not the floor course, but the base course of the walls.

Correct. I have a layer of perlite mix, 1 base course, 1course laying flat and 1 on end, equaling 7in. I built it to the specks of the Wisner's book. It's a concrete floor so I wanted some perlite to keep too much of the heat going into the ground.

I got my manifold made, my exhaust connected and ceramic wool wrapped. The wool is 2300 degree tolerant, used wire to keep it together. Over all my pipe run is 23 feet with 4 turns then the turn upward. Ran the pipe with a 2 in. rise over the 23 ft run. I will have a 2.25 in. Gap at the top between the riser and top of bell. Finally found a clay pit and will be mixing the cob hopefully today, at least start it. Once I get the exhaust fully supported I want to fire it up and see how it's going to fire and draw. Does anyone have any suggestions of anything I may be missing? Any advice would be greatly appreciated.

Lookin' good Jason! Any plans on putting some insulation around the burn tunnel and lower portion of the feed tube?  Just be sure to use lots of dense stuff ie. rocks, steel chunks, urbanite, whatever... to fill between the pipes to hold the heat longer and have much less cob mixing to do. Look  forward to your blastoff report!

I do have some rubble to pack around. A bunch of field stone and broken up concrete chunks. I mixed some cob up today. It worked out well but I found out my feet aren't as tough as I thought, lol. Also I have some ceramic wool left to wrap around the burn chamber when I start packing the cob. I want to mix more cob tomorrow after work. I'm wanting to get the cob done under the exhaust then to a fire up before all of it gets covered.

For mixing cob with tender feet, I sometimes put on a pair of rubber boots and stomp away. To keep even your boots clean, I'll fold the tarp over the mix and stomp on that. Sure, it may take away from the purist way of doing it but I find that it blends the mix just fine for me and hey, when its getting cold outside, this is gonna be the only way to keep me happy too!

Well, it worked! Started up second try. Seems like good draft. I'll upload a video soon. Only about a10th of the cob is done, but wanted to try it first before I covered it all over.

Putting out some serious heat. The second burn made my downstairs almost to warm. Can't wait to see what it does with a finished mass. I have one vent into the upstairs, the heat is just pouring up into the room. I'll be adding a few more. So interested to see what my propane bill will be with this RMH supplementing it. So happy I found out about this!

Jason, just a daft idea.

If ever you don't like the way it works.

You can always exit the rocket directly into the chimney, and  tap the heat from it,  to a mass upstairs.

You block the  chimney let say 12 inches above the floor upstairs, make a hole in it, with a pipe feeding your mass. Then return in the chimney above the blockade.

Pish easy to do!

I have done some thinking on it for sure. I was thinking down the road making a small mass downstairs, running the exhaust up into a second mass, then out. But that will take allot of supporting the floor upstairs plus cutting into an existing block chimney. Until then, my house will be much warmer this winter. Thankfully the draft is running strong. It dropped to 32 last night in Michigan. The heater fired right back up. The downstairs was still warm. Up stairs was still chilly, but I'm going to work on that.

I'm also going to try to run a vent to the back rooms. I'm going to try to turn it on when the burn is going, pulling heat from the barrel. I have some free vent pipe, just need to get a fan. I found one at Menards for a decent price. Only way to find out if it will work is to try it!

Michigan weather turned before I could finish the mass, but it pumps the heat out! It heats my basement 80 to 85 degrees, starting at 69 degree temp.  Maxed out to 90 once with a 3 hour burn! Takes about 2 hours of burning to get it to 80. Upstairs gets about 73 to 75 tops, but the floor is really warm on the feet. Floor gets even warmer if it wasn't for my flying saucer heat shield. Might stay more consistent upstairs if I burned twice a day. Right now only burning in the evening.

So upside, wood heat feels so much better than propane heat. Walls and floor really absorb the heat for a good period. Once the heater is going, I haven't had any issues with the draft or smoke back. Love the sound and peace while sitting by it! It's safe, by the time I go to bed, the fire is done burning, no over night burns. Burning mostly clean, hardly any smoke at all once it's on full burn cycle.

Down side. Does take up a fair bit of space, but I need to finish the mass. So that will probable change. Good and bad on this one: it takes some tinkering with to get it going, so not start up friendly for my wife to use, yet. But the plus side, I love tinkering. Using a little more wood than I thought, but I'm pushing more heat into a big space, so it's to be expected. But I have 11 acres of hardwoods, cutting fire wood isn't a problem. Also, if it sits for a few days, it fights me on start up, but at that point the whole system is really cold and it has to push back at a tall outside block chimney. Last thing I can think of, is the cost on how I built it. I bought all new products to build the heater, so it cost around 900 dollars. So there is far chapters ways to build this unit.

Over all, would I build it again, yes! I would change a few things, but most of that is with the house design, not the heater. I would look for some cheaper items to use, but I'm thankful I didn't have to drive far to get everything.

Places I bought the materials:
Menards for the block and duct work.
Blains farm and home for the split fire brick.
Phillips Energy for the full fire brick and ceramic cloth.
Barrel from a RV store.
Sand from my dad's property.
Clay from a farmer for 30 dollars.
Firewood from my property.

Let me know if anyone has questions about the build or setup. I'll let you all know how much propane I by this year!

Glad to hear your keeping warm Jason! That mass will be real nice to sit on once it gets finished.
As for the startup issue, do you have a cleanout behind the manifold/barrel area where the pipe goes from horizontal to vertical? If so, have you tried to prime the pipe with a piece of newspaper to get better draft at the feed tube?....or even cheated and used a fan temporarily to get things moving?

Gerry Parent wrote:Glad to hear your keeping warm Jason! That mass will be real nice to sit on once it gets finished.
As for the startup issue, do you have a cleanout behind the manifold/barrel area where the pipe goes from horizontal to vertical? If so, have you tried to prime the pipe with a piece of newspaper to get better draft at the feed tube?....or even cheated and used a fan temporarily to get things moving?

I have used a blow dryer to prime the exit pipe going into the chimney, lol. It helps when the system is dead cold. But if I run it within 2 days I don't have hardly any smoke back. Also I don't have a cap on the top of the chimney, so that doesn't help. Over all, I have only dealt with a couple smoky starts. Opening the window to get a good fresh air helps with the initial draw. About 10 minutes and it roaring on a cold start. Any smoke problems have come when I rush the start up process. But I might design a port later on in the exit to help pre heat the chimney or build a bypass for start up.

We have a nearly identical house configuration and situation of need for heating it----preferably from a RMH in the basement.  Thank you so much for the excellent description of your project, and the encouragement to us to go ahead with our plans/hopes.  

Jason Speaks, and to all the other RMH peeps, has anyone toyed with the idea of heat pipes. And a feed tube through the floor? I’ve been rolling this idea around in my head and what little I understand it should heat the upstairs rooms better than just stuck in the basement.  Each heat pipe could feed a room and the feed tube could be perforated to not mess with the siphon. I tried bouncing this idea off Ernie and Erika but got no response, I assume they were busy or thought it was such a dumb idea that it didn’t warrant a response. I don’t have a way right now to try my idea, maybe some day...