Wood Heaters – Radiant or Convection Alternative Building — Energy Matters Forum

Wood Heaters – Radiant or Convection Alternative Building - Energy Matters Forum

Wood Heaters – Radiant or Convection?

Wood Heaters – Radiant or Convection?

There has been some discussion re Wood Heaters on another thread and it has prompted me to ask a question that has been nagging away at me for years. So rather than hijack that thread; here goes!

Woodheaters come in two basic variants; Radiant and Convective, with some that combine elements of the two types of heat transfer. The vast majority of them on the market are convective and some of these are fitted with “booster” fans.

I suspect that most people buying Wood Heaters would hardly know the difference between the modus operandi of the two types; purchasing decisions usually being made on cosmetic considerations or at best by the clearance advantages of the convection types.

But, (IMO) there are other important considerations, the most important being building layout, ceiling type and building construction.

If I can use my case as an example; the house is mudbrick with large floor to ceiling mudbrick room dividers in the main living area that act as thermal masses. The insulated ceilings are Cathedral type and the maximum height is 5 metres. Windows are not double glazed.

But, the previous owner decided to install a purely Convection Heater! So what happens to the heat? Heads straight for the ceiling! And being Off-Grid, running Ceiling Fans to bring it back down is not possible. And I have to burn tons of wood to keep the house at a comfortable 20 degC. Minus 5 deg frosts are quite common here in NE Victoria.

I am replacing it with a Radiant Heater. Wall/drape/furniture clearances are not an issue, and we have no wish to heat the rest of the house; only the main open plan Kitchen/Dining/Dining area. My rationale is that the direct radiant heat will provide personal comfort, while heating the walls/dividers etc at lower levels where it will be re-radiated and also transferred by convection.

I believe that I am doing the right thing, but it does beg the question; how many designers are taking into account the type of heating to be installed when designing energy efficient houses?

For example, if one wanted to convect heat from a Wood Heater to other rooms, then lower Ceiling Heights would seem desirable as would a floorplan that assisted. But what about external wall construction? In this case, for example, would reverse “Brick Veneer” actually be detrimental?

Your thoughts please?

470rigby Solar Crusader

Posts: 129 Joined: Tue Oct 06, 2009 11:57 am

Re: Wood Heaters – Radiant or Convection?

Many years ago when I lived in town I welded myself a wood burning firebox heater from 6mm plate steel, and whilst it heated the living room at one end of the house very well by radiation and convection, not much of that heat made it to the far end of the house on cold winter nights. I then added a boxed in section so air could be blown in at the bottom front, which was then ducted up the back and across the top, for a real blast of hot air. More heat made it to the far end of the house. Then I tried using a ceiling fan, and the whole house became quite cosy. The very hot air that was trapped just under the ceilings, but above the doorways, was able to be shifted.

So, given your high ceilings, I think a ceiling fan would do wonders for your heat distribution, even just within that main living area if you dont want any going to other parts of the house. From memory (late 1980s!) the fan I was using drew about 120W. I didnt have to run it all the time, just gave it a burst on high for a few mins every now and then did a good job of evening out the heating.

I reckon its worth considering :

1/ a fan to blow across the convection heater, small fans that only draw 20 or 30 watts can shift quite a bit of air. Extract more heat before it vanishes up the chimney!

2/ a ceiling fan to be used intermittently to distribute the heat more evenly.

Less expensive than buying a new heater, maybe even if you need to add another PV panel to power them, if you are running close to capaicity already.

These 2 things are probably worth considering for a radiant heater as well, as the near-ceiling area will still become hotter than lower down.

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