Fireplace Cold air intake.

[Mrdjc]

Most modern stoves have a separate combustion air intake since modern homes are made practically airtight which can create a backdraft.

Looking at schemes there are two ways to introduce cold air to your fireplace, one is via a dedicated ventilation channel in your chimney, or via the voids around your chimney liner, although this is far from ideal as this air will be warmer than the ambient outside air and still try to rise.

The other alternative is to fit an external vent and run ducting under the floor to the cold air intake of the stove.

Question is, are there any rules regulating this?

Can you use ordinary PVC ducting?
Do you need to use metal ducting which is fire resistant, however I'd have no clue how in earth fire would make its way back into the pipe.

Will the metal ducting survive being underneath the floor with cold air rushing through it condensing on it constantly?

Hunting for a vent for the outside, is there one you can close to stop cold air coming in when the fireplace is not in use, with a valve?

Does anyone have any experience with this, I tried searching on google and its all very vague.

Ideally (in my mind) it would all be plastic except for the last 90 degree bend where it goes out of the floor up to the stove, as this could potentially transfer heat down.

 

[regsmyth]

Are you talking about a wood burning stove?
What size is it (heat output)?
Small stoves don't need an identifiable source of air, but larger ones do.
Your idea for underfloor ducting sounds reasonable, but I don't see that cold air will condense on the ducting, as it's the air thats cold, and the ducting will be room/floor temperature.
UK building regs might not be the same as Slovakian ones.
Sorry can't be more help.

 

[Mrdjc]

16KW Multifuel, but will be used on wood for the foreseeable future as we have a fairly large stockpile.

The ducting would be ran in the hardcore layer, under the blinding sand, insulation and concrete.

Temperatures can be quite strange in this country where at night it can be -5 and during the day +10, I am worried that the cool air will cool down the ground, and then start sucking in warmer air during the day, causing condensation (warmer air on cold metal surface). I don't see plastic having the same issues as they don't conduct heat as well.

Point is, is it permissible to use plastic for it as it is part of a combustion system, however I don't see how in earth fire from the firebox would make its way back down into the air intake.

Maybe only have the last 90 degree out of metal leading up to the stove itself, that way any embers or something that go backwards (through a maze of vents and stuff may I add!) and ends up in the pipe.

I tried reading up on it but I have no idea where exactly to find this kind of information, all I keep on finding is "People fit these systems and they are recommended" not "These systems are fitted doing XYZ because ABC in order to comply with ... "

What about the vent outside that can be closed using a cord or something to stop draft coming in when its not in use?

 

[regsmyth]

You may have a point about condensation, but perhaps you could use galvanised ducting.
I should think it would be ok to use plastic to within say a metre of the stove, but I really don't know.

You need to go to a stove fitters place and ask. Or talk to your local building control officer.

 

[Mrdjc]

Funny thing you say that, but they don't do all this building control stuff over here for residential buildings.

The only thing they want to see certificates for is Gas and Electricity, and that's only for insurance, a bottle of something to drink goes a long way in getting things signed off to comply..

 

[Mrdjc]

Well, went ahead and "did something" ...

Can be viewed on my renovation blog.
http://brit-living-in-sk.blogspot.com/2012/07/upwards-and-onwards-and-downwards-too-i.html

(Bottom half of post.)