The Pros and Cons of Direct Air for a Wood Stove (when there’s no mandatory requirement)

[Doug Tait]

10 minutes ago, GarethM said:

Do they atleast have the big screen TV pointing at you and the sound turned up ?

 

Unfortunately not, just rude 

[BillQ]

We have an older house so it was designed for airflow, however we also have DG and its a bungalow. We keep the lounge door open and a fan blows air into the hall to warm the rest of the house and keep us cooler as it can get up to 24'c easily with the door closed, 19-21 when open. Using the fan means we have a draft but its hardly noticeable. 

Our stove is 5kw and draws fine even when we are in the middle of storms no blow back. 

 

If our house was newer and therefore better sealed then we would have gone for external air but its not so we allow the airflow to keep the inside dry and mostly condensation free.

[GarethM]

2 minutes ago, Doug Tait said:

Unfortunately not, just rude 

Bloody inconsiderate of them!.

[openspaceman]

4 hours ago, BillQ said:

If our house was newer and therefore better sealed

and better insulated I wouldn't need to heat with wood.

[Steven P]

1 hour ago, openspaceman said:

and better insulated I wouldn't need to heat with wood.

 

living the dream!

[Alycidon]

I advise the use of a direct air supply when the stove is against an external wall,  this is part of our costings letter to prospective clients:

 

.

A typical 5kw stove will use around 25 cu m of air an hour,  if a direct air kit is installed then this air is drawn from outside the property, piped into the stove, burnt, then passes up the chimney.

If a direct air kit is not fitted then 25 cu m of hot air are drawn from the stove room into the stove, burnt and passes up the chimney.   This then depletes the hot air in the room.

So for optimum efficiency install a direct air kit if the stove can accept one.

 

If you have a short flue or one with bends in it then we STRONGLY advise direct air being installed.

 

A

 

 

[JMA46]

Hi all

 

Logic tells me that an external air in take will definitely have benefits such as stopping draughts and would asume the air intake could be controlled via a chimney valve / plate? My question is I am wanting to install a boiler stove 21kw to run rads and H/W. My chimney is central to the house, so no external wall and concrete floors. Could I use the chimney cavity to run an  external air feed for the boiler along side the boiler flue?

Maybe not have it terminating at he height of the burner flue, so it does draw any fire gases or even terminate in loft?

 

Thanks in advance

 

Joe

[Steven P]

Gut feeling is hot air rises and depending on the set up it could be possible to 'stall' the chimney - where the external air acts like the chimney, reversing the expected air flow and making the fire very tricky to get going. Particularly overnight at winter when the fire is out, chimney pots are at say -5 deg C, loft at 5 deg C  could see this happening. Smoke, fumes and any heat is pumped into the loft, best worse case is the smoke alarm goes off at silly o'clock in the morning with a false alarm, worst worse case is it isn't a false alarm.

 

Related to this is having a down draught of cold air next to the chimney cooling the exhaust fumes more than usual you might find the draw is reduced from this.

 

Not an expert in this though, just gut feeling.

[openspaceman]

1 hour ago, Steven P said:

Gut feeling is hot air rises and depending on the set up it could be possible to 'stall' the chimney - where the external air acts like the chimney, reversing the expected air flow and making the fire very tricky to get going. Particularly overnight at winter when the fire is out, chimney pots are at say -5 deg C, loft at 5 deg C  could see this happening. Smoke, fumes and any heat is pumped into the loft, best worse case is the smoke alarm goes off at silly o'clock in the morning with a false alarm, worst worse case is it isn't a false alarm.

I generally agree especially about incoming cold air cooling the flue too much and causing condensation of water in the exhaust. Even if the flue continued a few feet above the inlet air the path would be too torturous  for the buoyancy of the hot exhaust to drag the cold air all the way in.

 

In principle (apart from the condensation issue) the concept is the same as on a modern gas boiler, with a balanced flue, but that has a fan to drive the process. So I think it could be made to work with an induced draught fan at the top of the flue, driving the exhaust up away from the intake  as well as creating a depression in a room sealed stove to suck the air in, whether it would meet building regs is another matter.

 

[Muddy42]

Sorry I'm a bit following the last two posts here?.  My understanding was that the most efficient wood burners are the biomass central heating systems.  These have fans but not in the flue, in the body of the burner to supercharge the burning process. Granted they are burning all the time, unlike a stove.  Interestingly my ecoangus actually burns downwards - the fans initially push the exhaust downwards before they rise naturally and the heat is extracted via the tabulators.