Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Gravity, radiant heat, no electricty, wood fired

StewStew Member Posts: 22
I need advice and ideas. I need to design and install a gravity radiant floor system with wood fired boiler and little or no electricity. I live in S.E. Alaska where solar is no option in the cold months. I want to design the system BEFORE I build the house!


  • Uni RUni R Member Posts: 589
    Now that's a challenge!

    Gravity, wood fired and no electricity? Wouldn't the boiler need to be under the house? You could wake up in the Yukon!
  • brucewo1bbrucewo1b Member Posts: 638
    I would think Steam

    would be more prcaticle
  • Brad WhiteBrad White Member Posts: 28
    Big Pipes

    That would be interesting... as UniR says, the boiler would have to be below the house. The pipe sizes would have to be pretty large. If you did not pitch them you would need some kind of thermosiphon, meaning the boiler would be deep, below permafrost so to speak. (A tall column of water to afford circulation in all of that largely horizontal pipe....)

    Bruce has a great point about steam... steam being a gas will flow nicely with no electricity at all. Still would have to be below the floor of course.

    Control might be a bear. But then you already have bears up there, so what is one more?
  • Uni RUni R Member Posts: 589

    What are some of the particulars of the building site? Is it flat terrain? Neighbors nearby? ...
  • BoilerproBoilerpro Member Posts: 407
    Could hang the rads from ceiling

    that would keep the boiler at grade for either steam or hot water. Basically you'll have radiant ceiling. Gravity Radiant floor....HMMM!


    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • StewStew Member Posts: 22
    wood fired gravity radiant heat

    Well, grade isn't going to be a problem. I'm tired of having the wood stove in my living space. They're messy and a fire hazzard. Plus I want a BIG wood stove/boiler so I won't have to stoke it so often.

    The building is going to be right on my dock, about 16 feet wide and 36 to 46 feet long. The shop will be on the ground floor and my living space will be above. I'm thinking of building an insulated, stone boiler room that will also be my sauna. It will be 20 to 30 feet from the shop/house on ground level. I might build an insulated corridor from the boiler room to the shop to duct excess heat there.

    Building codes are not a problem, but I want this job as good as I can make it. It's going to be my home for the rest of my life and I want it as trouble free and versatile as possible. 10 to 20 years from now I'll probably have to be using oil instead of wood.

    If I have a good enough fishing season next year I'd like to hire at least a consultant, maybe a designer.

    Weather here is mostly pretty mild. I'm close to the coast and my dock is on an ocean inlet. We just got over what for us is a major cold spell; single digit temperatures for a couple weeks. Now we're back to usual winter weather, about 36 to 46 degrees.

    I'm also interested in heating my shop floor with water from the inlet, which is 40 plus in the winter. It would be nice to have a slab at that temperature when it does get cold, but I have no idea whether I could gravity circulate that or have to pump it, the temp. differential being only about 10 to 40 degrees.
  • jpjp Member Posts: 1,935

    if you live that close to the coast, don't you normally have wind?

    a 400watt air x generator, 200Ah battery and use a low wattage circulator?
  • Uni RUni R Member Posts: 589
    More for Brad et al

    Can steam be easily and reliable used to power a circulator?
  • StewStew Member Posts: 22

    I need advice and ideas. I need to design and install a gravity radiant floor system with wood fired boiler and little or no electricity. I live in S.E. Alaska where solar is no option in the cold months. I want to design the system BEFORE I build the house!

    Yes, I have wind but I'm trying not to add more moving parts. I'm already maintaining a commercial fishing boat (a wooden one no less), a couple gen sets, a sawmill, four buildings, a dock, float and ramp, two outboards, a backhoe (a real sick one), and now a satellite internet dish.

    I'm not complaining, life is good, but I'm only one guy since losing my dog in the divorce. I'm pretty good at keeping stuff going, as long as I have a nice warm, fairly maintenence free room where I can collapse or bang my head against the wall. So I thought a radiant heat system would help for a number of reasons.

    Thanks for your response though, I do appreciate ideas.
  • StewStew Member Posts: 22

    I need advice and ideas. I need to design and install a gravity radiant floor system with wood fired boiler and little or no electricity. I live in S.E. Alaska where solar is no option in the cold months. I want to design the system BEFORE I build the house!

    I don't know anything about steam. I have yet to obtain or build the boiler. I've been experimenting the last 10 or 15 years with various water heating (domestic water only) stoves and am on what I think is my last prototype.

    How safe, maintainence free, and complicated is steam?

    Thanks for your reply
  • Brad WhiteBrad White Member Posts: 28
    Steam Power...

    Steam for power and steam for heat are at completely different pressures. Steam heat we all know works best at low pressures. Generation with steam, even microturbines needs significantly higher pressure. I am not sure how low at this micro-level but power generation on a more practical scale is often at over 400 PSIG (thinking of a 460 PSIG system I designed for a 3 mW turbine in NH) and large utilities use over 2500 PSIG steam turbines. Think vapor versus a jet.

    The other part is, it would have to be two-pipe steam (one-pipe has to cycle to release the vents and get condensate back.) With two-pipe, you need to pump the boiler feed water, a parasitic loss but the only way to assure a constant stream of steam at a reasonable pressure.

    Good thought though!
  • Brad WhiteBrad White Member Posts: 28
    How safe, mainenence free and complicated is steam?

    Steam does not need a pump, no electricity for one pipe steam especially given that you are providing separate fire by wood. If the system is tight, water leakage will be minimal hence little new oxygenated water. Steam systems have run for a hundred years and some of the oldest are still going strong.

    Complicated? Every system has it's quirks but the principles are the same, air out, steam in, water back, as our Mr. Patrick Linhardt writes. Once the system is installed, the piping stays pitched if done right. The only moving parts are steam vents, easily replaceable items. A low pressure gas -ounces!- with gravity return. Such a deal.
  • StewStew Member Posts: 22

    Another reason I'm doubting steam is that to make it I'd need a more or less consistant temperature. My stove in the cabin (and my new system will probably be no different) fluctuates a LOT in temperature. Sometimes I leave with the boat for hours or days. Sometimes I can't get home even if I want to, so I'm aiming for something that will go for a while on it's own but be ok if I don't show back up for a big freezel. I'm thinking I'll need to use antifreeze in the system and probably a large-as-possible storage tank in the boiler room. That way the boiler temperature ups and downs can be leveled out some by the tank and a large-mass slab.

    Control systems is one of the things I'm stumped on. I maybe forced to use some battery-inverter power to operate some control valves, but I'd want it to work at some level if that power failed.
  • Brad WhiteBrad White Member Posts: 28
    I should have added

    that steam systems drain back to the boiler when "off" so there is no water in the space served at least. Not a guarantee that your boiler may not be done-in, but it can be protected.

    If not steam then gravity HW is the only other choice I can think of- and with glycol. With gravity HW you can have some modulation of temperature but you are right, not so much with steam.
  • hrhr Member Posts: 6,106
    Our friend Larry Weingarten has

    a gravity radiant system, solar powered if I'm not mistaken. He has posted pics here over the years. He should be along soon :)

    hot rod

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • G LyonsG Lyons Member Posts: 36
    Remember the Romans radiant floor.

    This is what I would look into. No water filled pipes or boiler to freeze up and cause total damage. A wood fired furnace below ground level and the flue gases going through a labarynth of pipes below the concrete floor. How about concrete blocks on their sides to form the flue chanels.. Laid flat and uniform they could even be the floor, maybe a thiner concrete slab over that, or maybe a wood floor. maybe a plywood floor with some carpeting. I think I'm onto something here. Now some planning so the floor would heat evenly....When you return from a trip and the place is bitter cold, build your fire to warm up the floor and a fire in the fireplace for more instant heat and your set. I rest my case!
  • Brad WhiteBrad White Member Posts: 2,440
    Excellent Thinking, George

    The Roman Pyrocaust or the Korean K'ang... nothing to freeze, one hot fire in the AM is said to do it for the day. Serpentine passages for fairly efficient combustion... eager to see how this pans out.
  • Kevin O. PulverKevin O. Pulver Member Posts: 380

    George, wouldn't you need to be able to clean the creosote out of the "flue blocks"? I'm wondering if maintenance would be impossible. How about some sort of masonry stove- what do they call those European things? Lots of thermal mass, and the flue doing lots of twists and turns inside the thing. (I don't know how they clean them)Kevin
  • jpjp Member Posts: 1,935
    hate to say,

    but i think the most reliable, freeze free system, no moving parts, gravity hot air! sorry.....

    our old hunting camp had gravity oil fed gravity hot air, no electricity involved, you could use this as a back up when leaving for time periods and use woood fire when home all the time.

    EDIT: i realize its nice to have a stand alone suana, but realistically the waste heat when finished suana-ing should be used in the house, thus inside suana.
  • Mike T., Swampeast MOMike T., Swampeast MO Member Posts: 6,928

    Without a basement (presuming such is impossible in your area of AK) you won't be able to make a gravity in-floor heating system. Even with the boiler in a deep basement such would still be extremely difficult as head loss through any practical size and length of tubing runs in the floor would be too great.

    If your solid fuel boiler has fairly large tappings for supply and return you might however be able to use gravity to get the heat out of the boiler by installing a storage tank as high as possible above the boiler. Such tank would need a generously sized heat exchanger as direct connection to the secondary (floor) would likely interfere with gravity circulation from the boiler to the tank.

    By sizing the in-floor tubing quite generously (larger diameter and/or shorter circuit length) than typical you can keep head loss quite low. Grundfoss and others are making circulators that require VERY little electricity while moving a surprising amount of water under relatively low-head conditions. Not sure though if they're yet available in the North America... Considering the ratings I've seen for such circulators, they would seem very well suited to solar PV & battery backup if not complete solar operation.

    Larry's gravity radiant system is quite ingenious. Instead of floors, he heats walls. Rather like an old "overhead" gravity system his supply rushes from the solar storage tanks in the basement to the TOP of the walls via a large pipe and then works its way DOWN surprisingly small copper tubes with copper "fins" as the water cools. Each of these small tubes only runs from the header running across the the top of the wall down to the header at the bottom--they do not loop up and down. Presuming that you have a significantly higher heat load and no basement I seriously doubt that this could ever work for you and you would likely be unable to establish any gravity flow with just a few feet of elevation.

    Even Dan Holohan says that steam is too "uncontrollable" to be used for radiant floors.
  • StewStew Member Posts: 22
    gravity radiant, I DO have a basement &SOME GRAVITY QUESTIONS

    I do have a basement, even better, actually. My living quarters are on the top floor of the dock, the shop will be under me, and the sauna/boiler room floor will be about 3 ft. lower than the shop floor. I figure on heating the shop with radiant heat on cold days (rare in Southeast) with ocean water that is under everything. That water is about 40 to 50 degrees in the winter. Extra heat for the shop will probably be surplus hot air ducted from the boiler room.

    I'd consider heating the shop slab with return from floor above, but I doubt my wood heater would keep up.

    As to forgetting about hydronics and going back to air, I'd really rather not, especially for my living space. Wood stoves are fire hazzards and they require a lot of maintenance, especially cleaning the flues of creosote.

    As to little or no gravity flow without substantial elevation, I would have to get something.... In my current cabin I heat an 80 gal. hot water tank for domestic use from my woodstove. The tank sits on the the same floor as the stove and coils plumbed in a closed loop from the stove to the tank heat lots of water pretty quickly by gravity. Top of the tank heats up first, eventually heating the entire 80 gallons.

    In fact, if I don't use enough hot water, things can get a little too hot. I've been surprised a few times that the safety valve hasn't popped.

    I don't know enough about convection/gravity circulation to say whether the fast circulation is mostly due to piping, sizing, distance or temperature differencial, but I'd sure like to find someone who could educate me.
  • Brad WhiteBrad White Member Posts: 10

    (Is that the Finnish plural?)

    The Scandinavian/Finnish/Russian stoves, big massive tiled jobs. The fires they burned were hot and they were built to take years of abuse largely because they were what held the house to the earth.

    I don't know if you ever could clean them or needed to, my understanding is that the hot fire and good draft (ducted in from outside through the floor) made for a very clean fire with little smoke. Never took one apart though.

    Well, as my Swedish relatives always said about theirs, "Orgy Borgy".

    Then again, whatever they said sounded like that. :)
  • Dave BelisleDave Belisle Member Posts: 68
    It might work

    Years ago I had a wood boiler tied into my oil fired boiler with three zones of baseboard . If we lost power I would open the zone valves and the flow check on the wood boiler. It heated the house quite well. Any sevice Tech has seen this happen when a flow check gets stuck open on a oil or gas system .....

    What I might look at is installing radiant on the ceiling as well as the floor. Feed out of the wood boiler into the ceiling radiant and return back through the floor radiant . I have never done it but I don't see why it wouldn't work...... Your only control will be your air inlet damper....

    Dave in NH
  • StewStew Member Posts: 22
    gravity woodfired radiant control issue

    I need any info/advice I can get on controls for a gravity system. I have VERY limited electric power, but is it still feasible to use electrically controled zone valves and thermostats? About how much draw am I looking at? I kind of think in amp-hours here, as the power supply would be a battery and inverter.

    And are there systems that would default to open if the power failed?
  • Mike T., Swampeast MOMike T., Swampeast MO Member Posts: 6,928

    You might want to study this document available at Heatinghelp in the Library

    Your current setup sounds rather like an old cookstove with attached range boiler for DHW. While I've never seen one working, old friends and relatives told me that they did their job pretty well.

    From your description of operation of your DHW tank connected to the wood stove, I doubt that gravity-driven flow is as fast as you might think. "Top of the tank heats up first eventually heating the entire 80 gallons" tells me you're getting moderate gravity flow--particularly from a cold start when temperature differential is extreme--with the flow slowing as the entire tank heats. Since the hottest water naturally rises to the top of the tank you will get a fair amount of hot water "pretty quickly".

    Don't forget that only a small portion of the output from your wood stove is going to the DHW tank--most of the heat is being given off by the stove to the room space.

    A gravity-driven hydronic system on the other hand strives to move as much of its heat as possible away from the boiler and into the radiators. As the pipes gradually roughen from corrosion (remember--these areopen systems) it takes ever higher boiler temps to achieve the same degree of circulation. While it can take decades, eventually you wind up with excessive fuel consumption, a very warm basement and not so warm upstairs--a circulator usually follows...

    Even with a basement, I really can't think of any practical way to use gravity circulation for floor heating. The piping would have to be relatively enormous with extremely short runs while still maintaining proper slope. Since gravity supply lines pitch up from the boiler and gravity return lines pitch down to the boiler (1" per 10' is good) I can't even imagine how you'd maintain "proper" slope in a horizontal panel.

    I suppose you could create a gravity ceiling and floor heating system but I don't want to imagine the cost or installation nightmare.

    If you really want a gravity system, I'd suggest using iron radiators--either from salvage or new. The tappings of modern panel radiators are probably too small for use in a gravity system.

    Note that individual (dare I say "zone") control in gravity systems came from hand valves on the rads. Modern zone valves likely have too much restriction for use in a gravity system. Motorized full port ball valves could be used but you'd need fail safe operation--automatic return to open position--in the event of power failure.
  • jpjp Member Posts: 1,935
    limited power

    since you have the co gen system, running small circulators is going to greatly simplifiy your project. are you using 100% of the possible power for this unit, 100% of the time?

    to start you're going to need to know your heatloss, otherwise we are all just guessing as to sizes of components.

    one confusing thing, you state you're right on the water, mid 40's water temp. seems running that water through your floors would be counter productive? i would work to maxiumize your insulation.
  • StewStew Member Posts: 22
    Ocean water to heat the shop

    Yes, 40-50 degree water doesn't sound very comfortable, but I only want to use it to heat my shop slab when the temp. is in the 20's or lower. A 40 degree floor is a whole lot more comfortable than a 10 degree floor.

    The only way to do it is with a pump; however, and since I just learned (thanks to this website) that water doesn't change in volume under 52 degrees, I'll have to determine whether I'm better off running an electric pump or burning yet more wood....

    If a pump could be run on solar (unlikely here in the winter), it would be worth the investment. Maybe I need a good, old fashioned windmill on my dock to run a pump! AHHHHHHHHHHHRRRRRRRGGGGGGGG MORE MOVING PARTS TO MAINTAIN!

This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!