new videos
hot off the press!  
    more about rocket
mass heaters here.

more videos from
the PDC here.
  • Post Reply Bookmark Topic Watch Topic
  • New Topic

RMH vs woodstove decision, heater location, etc  RSS feed

 
Nathan Pieper
Posts: 16
Location: Upper Midwest USA
1
bike duck food preservation
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
This is certainly a long inquiry, but seems most people willing to pipe in are usually seeking the most context possible so I'm just trying to get it all in there right away. First half of this is context for any input on whether I'd be better off with a RMH or a woodstove (or both). and the second half addresses unit location in the home and what might be causing headaches around wood heat. Any input on any aspect is much appreciated.

My wife and I are building a new home, which includes the luxury of designing the home around being heated predominantly with wood. I think I've explored a fair number of the more important factors regarding wood fuel heating, but I still really appreciate any and all insight from those with more experience, regarding heating predominantly with wood. So far I only supplementally heat with an older pre-epa reg morso woodstove, and have never seen or operated a RMH -though I'd like to, if anyone in Western WI or eastern MN is listening and would like to let me check theirs out let me know

The general context is a home sited in a tighter valley setting in western Wisconsin zone 4B. Home will likely be on walk out style slab with the back (north) side bermed/buried on account of the 16% grade of build site. South facing slope so we'll design with a bit of passive solar help , but not so much winter sun in these parts to focus too awful much on that. Steep bluffs due east and west in this specific site also minimize direct sun day length (low sun path too) in shoulder seasons. So the main focus is really on heating with wood, and doing it well. We'll likely keep the homes footprint in the 600-800 sf range, and build it two stories (with identical square footage) for a simple build, so 1200-1600 st total. Should be insulated relatively well (though I'm not sure how tight is too tight just yet?), with plenty of inherent home thermal mass given the finished concrete slab first floor, and abundant wood etc.

Anyhow I'm still debating between RMH and a woodstove on the grounds of radiant vs convective considerations, and cooking considerations. I'm not necessarily opposed to the idea of installing both (woodsstove would be a smaller one in that case of course), but I do worry it could be a bit redundant, potentially wasting money and living space to use both. There are a number of pros/cons to either method in my opinion, like respective size, use regiment, cost, reliability, legality, fuel size/format/volume, etc that all have their own implications that I think I have something of a handle on (though sharing things in those respects you find particularly advantageous one way or another wouldn't hurt to hear about).

But there are two questions about the general decision that I have yet to resolve, then a few theory questions too I think:

-The first is weather we can expect to heat an upper level to at least say 55 degress F, solely with a RMH in our area, again total home sf will be around 1200-1600 sf and we can at this point deign/build however best suits heating with wood on main level (or both if maybe small stove upstairs for example. Both floors will be as open a layout as possible, minus small bedrooms and bathroom(s) which could have strategic venting I hope, or tall doors just usually open. No major ceiling vaults or anything. To my knowledge, any wood stove or RMH or masonry heater for that matter have some combination/ration of RADIANT and CONVECTIVE heat. I expect a RMH, with the heat exchange barrel AND mass, could be something of a middle ground between the high radiant but low convective heat output of say a masonry stove, and the higher convective but less radiant (in terms of duration?) effect of a conventional woodstove. Is this accurate? One caution I've been given from a masonry heater owner I spoke with is that high radiant but low convective heat appliances may not heat a second level enough or as well as a more convective heater like a wood stove, given the second level's lack of radiant exposure. How big a deal is this? Is there still enough convective heat generally happening to heat a second level? What might be the measures to combat this disadvantage if it's valid? A thinner floor for example, that more readily conducts the radiant heat from lower level's ceiling, into the upper level? Some kind of active and or passive air movement strategy that increases a RMH's effective convective use? I should be venting the floor on the warmest and coldest side of the house anyway right? to get a passive air cycle going?

-Next heater choice concern is cooking. We hope to be able to cook predominantly with the wood heat appliance(s) to stack it's function during the colder/winter months. But If I only actively heat a RMH for two hours out of 24, just for example, it seems that would imply around a 2 hr cooking window for an entire day, with the other 22 hrs being more or less useful only for warming things up a bit at best. Are there ways around this? Do I then instead just burn two one hour fires a day, and have two one hour cooking windows? That might be workable. How sucessfull have people been cooking with a RMH anyway? I seem to see some images of them in general internet image searches, implementing more dedicated cook surfaces or ovens, maybe even secondary burn chambers? If these elements do exist, are they pretty tried/true additions to a standard RMH, or more experimental than anything?

If it is of any consequence for comparison, the kinds of stoves I'm currently considering are either, on the simpler end, something like a Pacific Energy super 27 or Summit, with maximum of probably 8 or 9 hr burn times, and generally low particulate matter and high efficiency, or on the less reliable but maybe more user friendly end, Blaze King stoves with mechanic thermostatic air intake regulation, catalytic combustors (which requires occasional replacement and precious metals), but very low particulate matter emission and 30 hour burn times with one full well seasoned load. Seems unrealistic but seems quite verified by knowledgeable users across the web on woodstove forums etc. Either of these stoves should at least in theory have a surface temperature of 400-600 degres for nearly the entirety of their full load burn times, which would be the objective most of January/ Feb, mean cooking at that temperature is possible at any time of day, because the stove will always be running.

Two less wood stove vs RMH questions, but something I'm looking for input on none the less:

-I know many buildings place heat sources/vents near colder walls/widows etc. Does it save fuel or just keep temperatures more even in the space, or something else? I don't completely understand how it is a net help in some way, if it is, and am curious to know. Is positioning a stove or RMH nearer or father from cold walls or windows etc is a generally good, or generally bad idea, and why?

-I'm also wondering if anyone has input on the more common reasons or solutions for getting headaches while running wood burning appliances. I suffer a mild headache every single time I run my current woodstove, every weekend in the winter basically, so heating predominantly with wood in the new space is therefore something that I am mildly nervous about, yet also really just encourages me to design things well. I figured it could be a pressure issue since there is not directly air supply to this stove, but cracking nearby windows for more air supply (this is on a first level "wing" off main 2 story home) doesn't seem to change things much. Draft seems fine, carbon monoxide detector doesn't speak up even when very nearby (since it seems that stuff will induce headaches!). My wife does not have this reaction at all, just stays happy and warm. Also, while I don't spend a lot of time around other peoples stoves, I don't recall such a reaction to other stoves of have been around. Any ideas? Doesn't seem like dehydration either as it comes on almost immediately when the the room really warms up, and is usually instantly relieved to a degree when moving to colder parts of the house or outside. The headache is accompanied by a sensation is presser and warmth on the ears, and sure feels relative to being in the warm air, but why should 80 degrees give me a headache at home with the stove but not at work where they keep thimgs warm. Should be noted the rest of the houses resting temp is quite low, we live at around 58 when not running stove, but I don't expect any home with a wood stove running doesn't have some dramatic hot/cold spots, yet I don't hear anyone else complaining of a headache.

If you got through all that, thanks for your ears and eyes and any input you might have would be much appreciated.
 
Joseph Johnson
Posts: 115
Location: Sierra Blanca, TX
2
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Just Curious. Why are you stuck on the two hour burn for RMH's? Nothing says you can't kick it up a bit when you want to cook. It certainly will not effect the heating except to extend the time it will radiate and keep you warm.
 
Glenn Herbert
gardener
Posts: 2180
Location: Upstate NY, zone 5
74
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks for all the detailed context information! It does save us a bunch of time.

First, don't denigrate your solar potential. I am near Binghamton, NY (zone 5), which vies with Seattle for the dubious distinction of having the most clouds and least solar potential in the lower 48. There are certainly many days where I can't even tell which way is South, but when the sun does shine, I hardly need any daytime heat even on the coldest days. I put most of my windows on the south side, but there is a lot of exposure of the building envelope in all directions.

I think your feeling of an RMH being a middle ground between masonry heater and woodstove is accurate, and well placed (near the stairwell), you will get sufficient convective heating for the second floor. I have radiant floor heating on both floors, and the main (upper) floor has a couple of partially isolated balcony/lofts without separate heat source. They are well heated most of the time, except in particularly cold cloudy or windy days when the heat loss overpowers the faint convective currents.

A floor structure of solid plank on beams might be good for direct conduction from first floor ceiling to upper floor surface. It would also give maximum spaciousness for a given building envelope height.

There are a few things you can do to maximize cooking ability with an RMH. In Zone 4 upper midwest, I think you will want heat every day for much of the season, and will probably need to burn more than two hours a day in colder times. This assumes your system is well balanced to the house. In your case, a J-tube might be better than a batch box, as the heat generation is more spread out. My beloved does all her cooking on her woodstove which is going 24/7 during the heating season (smoldering much of the time ), and based on the response time of that solid steel appliance, an RMH cooktop, whether barrel or more consciously designed cooking surface, should be able to serve well and be used with fairly short notice. If you want to do serious cooking on the barrel, I would advise setting the J-tube in a depression in the floor slab so the top can be at a convenient height. If you design the flue path so the chimney ends up next to the barrel, you can install a bypass damper which will ease lighting from a cold start as well as allow you to run a fire without heating the mass so much if desired.

The heat source near the coldest surfaces is strictly a comfort function, and will allow more heat loss while minimizing temperature differences in the space.

I can't speak to the headache matter, since you say the CO detector is happy (you have tested it, right?). Is there any possibility of a leak in the chimney or elsewhere that is letting some other pollutant escape?

 
Mike Cantrell
Posts: 555
Location: Mid-Michigan
28
bee books duck food preservation forest garden hunting solar trees
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Have you considered a tall masonry heater, rather than a wide one? The radiating surfaces can perfectly well be continuous from downstairs to upstairs, if you're building new. See rob roy's cordwood house, "Earthwood". Got a gigantic masonry heater as the center of its round, two-story layout. (I want to say it's 26 tons. Gigantic.)

As far as headaches, are you stirring up some ashes when you load? That gives people sniffles around my house, and sinus irritation can certainly trigger headaches.
 
Nathan Pieper
Posts: 16
Location: Upper Midwest USA
1
bike duck food preservation
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks for the input so far Joseph Glenn and Mike!

Joseph, good to hear that we could likely just throw some more fuel in to get the barrel or equivelant hot in pretty short order for cooking needs as they arrive. I honestly don't know enough about RMH yet as to have made the assumption I could do that without overshooting on the intended heat output.

Glen, glad to hear some positive feedback on likely getting enough convective heat upstairs to keep things reasonable. I won't discount passive solar gain, and will plan for it and take what we get, just won't count on it.

We are hoping to be able to build the ceiling/floor "plank on beam" as you're calling it (I've never been sure what to call it), partly for heat transfer's sake (sound transfer too though I'm sure, whatever), partly for utility's sake (I'd love to be able to just tap in trim nails and hang things as needed for example), partly for the spaciosness (I'm 6' 4" and want a compact home for heat efficiency's sake), partly because I think structural transparency is useful and homey, and partly because I'm interested in omitting materials (like ceiling drywall) and other frills wherever possible or reasonable to save on expenses. Only problem is I haven't been sure how to pursue a floor like this without doing full timber frame or something which might be (likely) out of the budget unless I do a lot of self assembly. I've been considering that, but that's a whole other can of worms probably not for this forum. Starting next weekend though, I am meeting with several generally conventional home builders to start getting ballpark bids on stick frame variations to see how small we have to ultimately build to stay in budget. After that I can really start nailing down the design. Is "plank on beam" a known or at all common ceiling/floor system for modern stick framing do you know?

I'd also be curious to know a bit more about your experience with the radiant floor and heating with RMH in tandem, since that may very well be my final scenario as well. Since it's a new build on slab, and everybody and their brother is telling me I would be reaaaaal stupid not to at least put the radiant floor heat tubes in, I have been leaning the way or radiant floor with respect to the backup/conventional heating system that would in theory only really get used in the event of winter travel or illness etc. local plumber just has an on demand electric boiler he says, and buys off peak electric for it or something. Seems like maybe the ticket for very occasional use and minimizing standby losses but I've not decided. One question that's been bother me (not that NOT having radiant floors would fix it) is if I'm living on a finished concrete slab on the main level, with radian't floor option, but don't actually (rarely) USE it (that being the goal) is it unreasonable to expect a RMH or wood stove to be able to prevent the slab from constantly feeling cold as ice? Or am I going to find myself running it just to keep the ankles warm? If thats the case then maybe I put down an overlay with less heat transfer, but again, I'm trying to keep materials to a minimum wherever I can. I'll likely just get some nice moccasins, maybe a few thick rugs too, and compression mats at sink etc. I'll be insulating below the slab of course. Stove folks have told me that radiant floor and stoves are a great combo because the floor is generally slow to tackle dynamic temps swings, and thats where the stove can step in. But in my case, I really just don't want to run the conventional system, whatever it happens to be, outside absence or illness. Still trying to figure out what the best system to rarely use is haha. Some have just suggested regular old cheap electric baseboard or wall units, but if I already have the floor tubes in.... and if the baseboards encroach on space and look stupid.... tough call for me still. Electric radiant floor? How bad an idea is that?

Thanks for clearing up the heat source close to cold surface dynamic being a pursuit of comfort, not efficiency. I thought I read somewhere though that radiant baseboard below a bay of windows for exmaple actually works to counteract heat loss at those windows. Idk, seems to me it would just more readily send that hard earned heat out the window to outers space.

The details on the rocket mass setup seem helpful, I'll refer to those ideas if/when I settle on doing rocket mass. Thanks.

Have tested the co detector. Maybe a leak in chimney but doubtful, its a straight vertical run

Mike, it could be a consequence of ash inhalation while loading I suppose. I might explain why wife has no problem, I'm the one messing with it, and do load more often than is typical, doing many half loads rather than a full. But it doesn't explain the alms instant partial relief when departing from the stove room.

Mike I haven't considered a tall masonry heater mainly because I don't think I have the budget to hire a mason. I expect a true masonry heater to be out of budget unfortunately, given prices I've heard quoted. I've seen exterior photos of that cordwood house you mention, but not the interior or its heater. Does sound a little gigantic for my application. Thanks for the idea though.
 
Glenn Herbert
gardener
Posts: 2180
Location: Upstate NY, zone 5
74
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
For info on plank and beam flooring, this will give you an overview, and probably enough technical info for a builder:
http://www.awc.org/codes-standards/publications/wcd4 (free online viewing).
I'm not sure it will be cheaper than conventional flooring as that has familiarity and mass production advantages, but the aesthetics and function could tip the balance. It should be possible to integrate this floor framing method with stick framed walls, with a little attention. Second floor plumbing is the major layout issue, and with good planning you should be able to avoid weird stuff.

I'm still building my home RMH, so I don't have experience with tandem operation yet. I can say that the tubing in the lower floor slab works wonderfully, while tubing below plywood subfloor is not nearly as effective. For backup, I wouldn't even worry about trying to do the second floor; you can open doors and use an extra blanket in the event it is needed.

I would consider laying out the water heater with a reservoir tank so you could heat water with the RMH too. This would need to be allowed for in the initial setup, but you wouldn't have to build it in at first. A solar hot water drainback collector that can also feed the reservoir would complete the versatility; again, with planning it could be built later. I would keep collector and tubing and probably reservoir bulk separate from domestic water (with a heat exchanger for DHW). I built my tubing to use DHW, and will probably replumb it to be separate when I build the solar collector (can't happen until I add the living room/MBR extension).
To be clear, I have a Polaris propane water heater which is sized to run everything. For occasional use, especially if it would mostly be running while you were away, an ordinary water heater would probably be able to take care of backup heating.

A tall masonry heater can be built with RMH technology, and if you are handy and can get competent with brickwork you can do it yourself. Code does require a professional to be involved, though, and code doesn't cover RMHs at all, so you could have issues with building inspectors. Feel out the local officials before you finalize anything; if you say you want a variant on a masonry heater, they might be more receptive. The low standard bench style has the advantage that even if it falls apart it can't fall on anybody.

 
You didn't tell me he was so big. Unlike this tiny ad:
2017 Rocket Mass Heater Workshop Jamboree (early bird price now)
https://permies.com/wiki/63312/permaculture-projects/Rocket-Mass-Heater-Workshop-Jamboree
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
Boost this thread!