We have two open fireplaces in this housed we just moved into. In the longer term, one may get replaced by a wood burner. I'd like to arrange for outside air to be piped in so that no room air (roughly speaking) need be used to feed the fire(s). Is this anything that folks do and if so how routine is it. House is 1930 approx.
The layout is two sitting rooms with fireplaces back to back. Can't tell if first floors also had fireplaces. What is the likelihood that the two chimneys for the ground floor fireplaces would be merged at a higher level in the chimney? If they are, and we need to line the chimney for a wood-burner, does this mean that the other fireplace becomes completely unusable?
Very unlikely. You get all manner of problems with joined flues, smoke from one coming out of the other fire place depending on wind direction or which doors are open or not.
Air supply, arrange a suitably sized vent, in relation to the size of the stove, to arrive near the stove. I don't think many stoves are "room sealed" when the door is shut.
Dave Liquorice wibbled on Thursday 07 January 2010 00:20
Yes, the instructions should be clear. Below 4.5 or 4.7 kW, I *think* you don't need an air vent, but double check. Having extractor fans or other combustion heaters including cookers in the vicinity affects this of course.
If it is decided to (by the book) have no air vent then you (OP) wouldwant to see the installer perform a smoke test with every door and window tighly shut including trickle vents. Or buy a box of smoke matches (eg BES) and confirm that when the fire is running, that every air input into the stove sucks the smoke off the match obviously and clearly.
Re the flues = I've never seen merged flues either. No, lining one flue doesn't make the others unsuable.
The only way chimneys to downstairs are "merged" with upstairs is where you have broken feathers between the chimneys. That is easily spotted with a smoke test (or pressure test) where smoke comes out of the wrong chimney.
Wood will almost certainly require lining (flames can go a long way up the chimney re outgassing of wood), gas fires less so (but nasty acidic byproducts & CO) - it comes down to the tests, simple as that.
No requirement for vents with gas fires < 7kW input where the spillage tests pass ok (with all extractors running, doors shut etc). You still need some ventilation into the room - historically provided by single glazing. Wood burning produces the highest temperatures and has other requirements re ventilation (a wood burner can heat an entire house, give you a suntan at the same time and still say "I have more").
You are very wise to duct air direct to any fire, that way it avoids
1) drawing cold air through a house depleting any other heating system you have 2) creating draughts through the house & within the room. Gas fires are notorious for "sucking the rest of the house cold", if the pull is excessive a door sausage is excellent at just taking the edge off (they do not block a door, they merely reduce the area from excessive - some doors have 12mm gap under them).
When I fitted a wod burning stove to a bedroom, I fitted a short pipe from the fire area to the ventilated loft, ..in is NEVER draughty, and feeds the fire perfectly.
I was more thinking about the two downstairs fireplace chimneys being merged at first floor level to make room for first-floor fireplace chimneys. There are no obvious first-floor fireplaces but there is evidence of a blocked off fireplace in the front bedroom (vent in the wall and obvious added piece of skirting board).
I would not contemplate installing a wood stove in a previously open fireplace without lining it properly - wood smoke is not nice it can be tarry & corrosive to the masonry of the flue, and due to the stove;s design (almost a sealed box) be cooler (and thus move slower and be more likely to condense out those nasties on the masonry).
coal has its moments (on a multifuel stove)
Nah - a properly installed stove will not be creating that much draw - you would expect to be closing the vents down on the stove to *limit* the amount of air entering it and thus rate of burn & heat....that's how they work innit??
In fact, the instructions, at least for a smaller stove may require a smaller flue area than the one provided by a normal chimney in order to maintain updraught - again, stove instructions will specify. Agree with all the other points though.
I was recalling open wood/coal fires which can get so hot the chimney draws like a hurricane. Stoves exhibit it far less and offer many advantages, kW output can be more tolerable too.
I think the old open wood/coal fire were as much based around the chimney being a massive "storage heater" for the house.
indeed - that's probly why the OP is looking to install one :>)
except that potential hurricane of draught going up it day and night lit or unlit would soon cool things down!
Open fires and associated flues,chimneeys etc are a crude heating concept and are mainly cooncerned with getting the smoke from cheap (as was) coal/wood out of the house - anything else is purely accidental.
Precisely what is a "smoke test" ? Is there a standard? Visible online?
In particular, is a chimney still expected to "suck the smoke off the match" when there's no fire lit? Chimneys work by the updraught of heated air, and matches can't be expected to heat the air on their own. Is the practice to test a cold chimney with a match, or with some "test fire" burning, so as to encourage updraught?
Andy Dingley wibbled on Thursday 07 January 2010 17:05
Application 1 - Verifying the appliance is drawing air correctly, not spilling fumes into the room:
*Very basically*, light fire, give it a few minutes to warm up, take source of visible smoke (this is where the smoke match comes in, but I guess a joss stick might work well enough) and hold it near the various air intakes the fire has. If the smoke gets pulled into the air intake then the fire is definately not bleeding fumes out there. Repeat for all air intakes.
There's possibly more to it than that, but the above proves a valuable point (you aren't getting a roomful of fumes).
Application 2 - Verifying the flue isn't leaking:
You can get more powerful smoke emitter devices which can be useful for verifying a whole chimney because you can wander round the house and attic looking to see if the smoke is coming out where it shouldn't.
Test fire as you say - you need it warmed up well enough to have an updraught going. This is how I saw a CORGI bloke do it: With the appliance removed, light a small test fire in the base of the chimney. When it's drawing, kill the fire and insert smoke generator. Check that the smoke is going up the chimney, then leave it going and wander round upstairs and in the attic looking for smoke coming out from places it shouldn't, like under the floorboards, between pointing in the stack etc.
I'd feel happy doing that to an open fireplace, but I don't know the details of doing the test in other scenarios...
Andy Dingley wibbled on Thursday 07 January 2010 17:05
Sorry missed this.
Not that I know of, I can only say what I've seen various Pros doing. They didn't seem to make a big deal out of it, in other words it didn't appear to be a precision science, just an indicator (cf. wandering around checking new plumbing for leaks but looking for weeping and drips vs. doing a hydraulic test to working pressure + percent)
The Hetas chap I had did a very basic test - he just looked around, saw I'd taken his recommendation on vents and lit a small test fire and noted the smoke going up the chimney and out the top.
HI, I piped air in to a point behind the woodburner, but, on reflection have obstructed the air somewhat to encourage more circulation of the air inside the house to aid convection in drawing cold air from the back of the house where it falls down the stairs...and in turn allowing the warm air to rise upstairs. It seems a balance is called for. In the past, with suspended floors, I put a vent in the skirting board and cut plaster away behind so the air was drawn through the underfloor crawlspace and the airbricks in the outside walls thereby assisting circulation of air to the floor joists. David
Other thing - look up the ground floor flue. It almost certainly goes off to the side to miss the upstairs fireplace, which itself is probably offset to the other side.
BTW, really old buildings did combine flues. I don't know the date when this stopped.
don't recall seeing 'em much on period TV dramas etc - wonder when were they invented...
aye...probly get some useful infra-red off the internal elements of the (exposed) stove pipe (tho less if some fashionista has had it done in polished stainless ;>))
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