I had scrolled through a few older threads on wood-burning stoves, but this topic does not seem to have been addressed.

So the deal is: We are putting in a wood burning stove, and the person doing the installation says that we have to install an air vent from the outside. It's not like this place is airtight (built 1845). We also have an air duct/exhaust above the stove.

I dug around, came up with a few sites, in English:



And in french: http://www.acqualys.fr/page/regles-de-pose-de-grille-d-air-et-condu... and http://www.bricozone.be/fr/poele-insert-pellets/t-prise-air-exterie... and https://www.poelesabois.com/installer-un-poele-et-un-conduit/choix-... and http://www.debusquer.info/chauffage.bois/poele.a.bois.php.

What is the experience of others who have installed a wood burning stove? If you put in a vent, what size was it? Our stove is going to be 8kW. So we might need 50 cm2 (~7.8 sq. in), if this site is correct (https://www.poelesabois.com/installer-un-poele-et-un-conduit/choix-...)

And no, I have no real confidence in the "artisans", less so in that their record of keeping to schedule and showing up on the scheduled days is pretty doggone pathetic.

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Back to first principals.

You need a supply of air to burn logs.

Air comes from outside.

Air from the outside is cold

Air indoors is warm

You want to burn cold air and logs to produce heat

Therefore you want the source of the cold air to be as close to the wood burner as possible so that there are no cold drafts.

A vent under the Wood-burner and connected to it would be perfect, so that all the combustion air is supplied from the outside and the heat from the stove warms the room.

The most modern stoves, designed for BBC (Eco) homes, do just that.

Me? I've got a classic Godin (output c 13Kw) with a 180mm chimney and a 160mm air vent from the vide sanitaire immediately beside it. Connected to 230mm twin wall conduit for the hot exhaust where it passes through ceiling and the loft. not all artisans are qualified for the installation and commissioning of log burners. There have been issues with some Anglais experts who quite frankly should be charged with attempted murder for their total disregard of any Standards.

I like the concept of  that, but I do not think we can run the air vents that way. We are adapting this to an old house, mitoyene/mid-terrace/rowhome (different terms, but same thing). So we have neighbor walls behind the firelplace. As it is, we have to run the exhaust duct up 3 levels, and then a very high attic. 

I was thinkig that we may have them put it at the far end of the room, above the frig, so we do not feel a cold draft as we are sitting in the salon.

As for the installation, we have a copy of ther professional insurance) and I have learned that you really need to watch pver them . The installers are French, not English.

Now that you mention it, an intake duct alongside the exhaust duct would be the best solution. Might be an argument here next week.

 Here is the link to an earlier discussion on here about cowboy installers with a few useful hints about chimneys etc

Your duct should extend downward from the ceiling to close to the bottom of your woodburner so that you are keeping the hot air inside the room. Your total vent size should also take into account any VMC or other extractor fan(s) you use in the kitchen and W.C/bathroom.

It might be a leaky old house ATM but almost everyone wants to draft proof in the winter!

A ceiling vent will not work

Sorry thought you meant a duct beside your 'exhaust' duct 

Quote - "Now that you mention it, an intake duct alongside the exhaust duct would be the best solution"

I am going to float that idea when they are here next - to run an air intake down the chimney.

Otherwise, it will be on the far side of the room (long, skinny cuisine/salle a manger/salon) so the air can warm a bit before it gets to where we are sitting.

Be careful  the fresh air entry is not in a low or negative pressure zone on the roof as you could end up with a double whammy if it starts sucking!

 Provided that its in the same pressure zone as the chimney outlet should be OK  (à la balanced flue?)

it will be if it is physically joined to the combustion air inlet on the wood burner like a balanced flue heater where pressure changes are the same on flue & combustion air & have no effect on the flame stability.  If not it could try to suck air out the room & hence down the chimney if there is no other relief available in the room. The other problem could be the air wash system on most fires which effectively means that the combustion chamber cannot be sealed & therefor cannot be considered to be a "balanced flue" type of appliance.

David Rosemont mentions the Baxi fire which took its air for combustion from under the “dummy” floor.  I used to work for the makers, Baxendales, some 50 odd years ago, my mother still has one of their fires.  The point is, as I remember it: a gas fire needs to change the air in a room 3 times per hour, a coal fire as much as 10 times and a wood fire is somewhere in between - so, either lots of draughts or, as per Roger’s info: a vent as close to the fire as poss.  I know it’s not true of many French houses but if you have a wooden floor with a space underneath it then you’re on a winner as the air drawn in from outside and under that floor, to a vent set near the fire, will be good for it.  Our place is like that and has air bricks around the base outside - so that’s in the snagging list - along with the other twenty million things...

BTW, when I was young and working for the Gas Board, I once visited a house where they were complaining about a “Gas Miser” burning badly.  The man of the house was permanently bed ridden with chest and breathing problems.  The wife had, kindly and considerately, blocked up every possible source of draughts into his room and sealed the windows very efficiently.  The fire was burning badly because it wasn’t getting enough oxygen, as a result, it was kicking out CO² into the room.  She was literally killing him with kindness.

We have fitted a C02 detector plus a few normal smoke detectors round our quite old house. I agree about the need for ventilation. Baxi fires in the UK used to have an underfloor duct which emerged under the grate. Certain models also had an ashtray which was accessed from outside the house. Going back 50 years! The cowboys are not all Brits by the way!

Sorry I don't get this at all. In this house we had an open coal fire then a closed coal fire both of which burnt both wood and of course coal.  The only time we had a vent installed in a wall was when the house was converted to gas central heating. So my question is why do we need a vent for a wood fire ? 


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