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Room heat transfer? Answered

Greetings all,

I live in a solar powered house which is heated by a single log burning stove which is situated in the main living area.

Is it possible for me to transfer heat to the colder rooms by simply putting ducting between the top sections of the adjoining walls (seeing that hot air travels to cold areas - in theory!) or will I have to use a fan? I am trying to use as little power as possible or ideally non at all.

Has anyone got any experience of this or know of any suitable solutions?

Many thanks in advance.


I know people who have this year installed a log-burning central-heating system, with pipes & radiators. Their design relies upon liquid convection / gravity for circulation (yes it works)


Large squirrel-cage fans (like the ones used in furnaces), use several amps of power. However. some small "muffin-fans" only use a few watts and blow quite a lot of air. The drawback is they make a bit of noise. You could use a standard light-dimmer to slow down the muffin fan to compromise between fan noise and air flow.... and only be using a few watts of electricity. You could use some 4-inch pvc pipes to duct the air from one location to another using the muffin fans. Another kind of squirrel cage fan i have seen in the stores uses a SMALL motor that turns several VERTICALLY stacked squirrel cage units. They are the tall looking ones they sell at all the outlet stores. They are not so noisy, and they move a lot of air... howver they are pricey... about 50 to 60 dollars (US).

Many thanks everyone for the suggestions.

I measured the temperatures in the main room and the adjacent bathroom (24c in the main and 8c in the bathroom - not inspiring for a long shower!) I live in New Zealand up a mountain and it is the middle of winter here! The ceiling height in all rooms is 240cm and the distance between the rooms is about 10-15cm (cavity wall filled with insulation)

Today I shall make a 100mm wide duct between the two rooms and measure the temperatures, I also brought a small extractor fan kit yesterday but I am not really keen to run power to it as the solar batteries are over 10 years old and dont hold much charge. Hopefully the duct will make a difference and if so then I shall make a few more.

Again thanks for the replies - I'll keep you posted of the results!


6 years ago

Not knowing exactly what you have in terms of ceiling heights, room openness and such its a little hard to make recommendations. But there are some things to keep in mind. Convection heat does work, but its efficiency will depend on the design. Heat rises and flows or pools depending on the house geometry. A wood stove in a single room generates an air flow from the heat rising to the ceiling and then cooling and falling back down to the floor again. if your stove ever lets smokes out you can watch this happen. If you have a typical room with doors the heat will pool at the ceiling until it reaches far enough down to flow through the doors. An opening at the top of the ceiling will allow the heat to travel through the wall to the next room effectively making it all one room. My stove is in a room that is about 3 feet lower than the rest of the house and the heat flows across the ceiling continuing on up to the rest of the rooms. Sometimes the stove "puffs" smoke and you can actually see it follow the ceiling to the rest of the rooms. (My stove is an older air tight Earth Stove and sometimes after you add new wood the smoke literally explodes in the stove when it gets enough air and it puffs out the door.)
Anyway, it will always be much warmer at the ceiling than the floor unless you do something to actively stir up the air. A ceiling fan will work for a single room. Ducting with no circulation fan will work to a degree if the ducts are in the area of the convection currents but you will still have cold floors. A simple solution would be to make your own ducts with the intake at the top of the ceiling of the room with the stove and then with a fan assist pushing the warm air out at floor level in the other rooms. A simple 1/4 plywood box duct box would work and you can cover it with wall paper or something to make it match the walls. A regular box fan at the ceiling, securely mounted inside the box duct would be enough to move a lot of air to the other rooms.

Whether you utilized ducts or not, they would require fans in order to move the hot air (otherwise you'll just get condensation build up and little air flow), so in my opinion, using a ceiling fan (directing the air flow down) is more efficient. (They also do wonders in the summer for drawing heat up and cooling rooms.) How well that will work however is in direct respects to the stove itself. Much like a radiant heater, they are designed to heat a certain square footage and nothing more. In order to "spread" the heat, you'll end up over heating the main living quarters to try and warm the other rooms.

There are many types of eco-friendly options for heating smaller rooms that don't require a huge power supply. For example, we have our basement on a separate heating system using radiant heat. The tubing runs hot water through and uses much less energy than a forced air furnace. If the rooms you are trying to heat are bedrooms, you might find that baseboard heaters (connected to an independent solar/battery supply) would be sufficient to program and heat only before you turn in for the night.

Let me know if you have any questions. ;-)

Hmm. Don't see why you get a condensation issue, convection currents may well be enough to get a flow of air going, if they aren't too small.

Agreed about the convection currents. If there is an opening between rooms at the top and an opening near the floor the warm air should flow out the top and cooler air in thru the bottom. A small fan would should help thing move along though.

Yo're right ! convection works, often, but not always ! Cheap, small, low powered , low SPEED fans may be just the ticket. Too fast a fan spin, and you'll have instrusive noise I suspect ?

Now that I've re-read the question and Re-designs comment about an opening at the top of the wall, I think I misinterpreted the OP. I was envisioning a length of ducting that would carry the heat from the living quarters to the other rooms, which being full of hot air against the cold zones could create condensation.