Visited a long time customer today. She's had a coal fire place installed in a room with a suspended [sub ventilated] floor. No carpet. I've been advising for ages to insulate this floor but the chap who fitted the fireplace says the sub-floor ventilation is necessary to ensure that the chimney draws effectively.

Anyone have an opinion as to whether/how important this is?

Obviously I advised against the open fire in the first place.

I draught proofed my windows and door.....great..........then I had to drill a dozen 22mm holes in the back of my fire through to the outside......once you have smoke in your living room, insulation suddenly seems unimportant.

Yes part J of building regs requires that an open fire be vented. Otherwise your customers installation would be prone to leak carbon monoxide into her living room! It is possible to use existing vents, like sub-floor ones. In removing these for insulation, you have a duty of care to replace the vents with some other way to ensure the fire draws..Wall vent or loft? The size calcs are easy to do. Whisper me if you need it

standard openings are about 600 mm square, let me know if very different. As posted, you will need to make a fixed opening that the customer cannot close.

Or maybe not!

How does all this fit with the availability of fire boxes that have an air inlet direct from the outside as opposed to from the outside via the room and it's leaky floor, air brick etc?

(We're looking into the "kacheloven" or mass heat store ... anyone with experiences?)

MikeRumney- My log burner has a supply piped directly to it from outside and my BCO is very happy with it. It can get all the air required from outside (there is a limit on number of bends etc and min pipe dia) but this should then stop any draughts from air bricks etc. All cosy and happy!! At least I will be when I finish my house.

Thanks Gusty that's what I thought ... anyone come across mass heat store or "Kachelovens"?

Posted By: Peter Clark

Posted By: MikeRumneyanyone come across mass heat store or "Kachelovens"?

Have you read this thread?
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=491" rel="nofollow" >http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=491

Yes, thanks!

I don't see why you couldn't core drill a hole through the back of the fireplace to the outside & fit a fireproof vent pipe (not plastic). However, I'd recommend you first get rid of the open fire. Some have been shown to have negative efficiency, i.e. they lose more heat up the chimney in a year than they deliver to the room in a year. A wood burning stove is much more controllable. Some come with external air supply kits which allow air to be piped in from outside avoiding draughts whether the fire is lit or not.

David

Hi dandyclub - a stove would certainly be more efficient, but if for some reason you are constrained to stick with the open fire, there are some things that will help, or so I've found.

Have the hearth as low as possible - below floor level if you can - and then have the top of the fireplace opening (or hood) also as low as it can reasonably be. Warm air in the room will be held in the room down to the height of this top level, and the cool stratum of air being drawn into the fire will be as low as possible. You may still have cold feet, but your knees will be warm.

Fit a baffle in the flue and experiment to see what opening gives a reliable draft; open say 50% more to be on the safe side and then fit a stop so it can't be closed further, but can be opened more if occasion demands. This minimises the excess flow of air up the flue, cutting down drafts and wasted energy.

Ensure that wherever the supply air is coming from it is not turbulent by the time it reaches the fire. This reduces the chances of smoke escaping into the room.