Gas fire installation

Just bought a flueless fire from Focalpoint, the Plasma, details here:

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we fully intend to get a CORGI to install it for us but I'm just a bit puzzled by one thing in the installation and user manual. If anyone's interested, the full manual can be downloaded in pdf form here:
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'vejust had an old Baxi Bermuda back boiler and its associated fire frontremoved and the plan is to brick up the fireplace opening and wall-mount thenew flueless fire on the chimney breast. Consequently, the bit that I'mbothered about though is this (paragraph 3.0):**If the appliance is to be sited near a disused natural draught flue it isrecommended that the old flue should be partially sealed off to preventdraughts, however some ventilation will be required to prevent condensation.The appliance is designed to be wall mounted.**Where would the condensation that they mention take place? Within the nowdisused flue? In the new fire itself? In the room?Cheers,John

Reply to
John
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We've

In your room I'd guess. It may have a catalytic converter but you're still going to be making lots of water vapour, just like a free standing calor gas heater. Not sure why you'd go for a flueless fire when you have a flue.

Tim

Reply to
Tim Downie

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>> We've

Thanks Tim.

It does say elsewhere in the manual that "A minimum of 100cm sq purpose provided ventilation is required for this appliance" but the way that they later say "the old flue should be partially sealed off to prevent draughts, however some ventilation will be required to prevent condensation" just made me think that they meant that you should also have some ventilation around the old flue. As I said, it'll be a CORGI who does it for us anyway, just me being curiously thick :o)

Why go for flueless fire when we have a flue? Just purely because we like the look of it. We're just refurbishing the living room and fancied getting rid of the chimney breast altogether but it's far too big a job and far too expensive. However, we do really like the look of these fires and it fits in well with how we see the finished room.

And it also does no harm whatsoever that these flueless fires are 100% efficient. 2.6kW goes in, 2.6kW comes out - no heat loss up the flue and given the current price of gas and what it's predicted to rise to that can't be a bad thing in my book.

John

Reply to
John

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'vejust had an old Baxi Bermuda back boiler and its associated fire frontremoved and the plan is to brick up the fireplace opening and wall-mount thenew flueless fire on the chimney breast. Consequently, the bit that I'mbothered about though is this (paragraph 3.0):**If the appliance is to be sited near a disused natural draught flue it isrecommended that the old flue should be partially sealed off to preventdraughts, however some ventilation will be required to prevent condensation.The appliance is designed to be wall mounted.**Where would the condensation that they mention take place? Within the nowdisused flue? In the new fire itself? In the room?Cheers,John

Within the disused flue. A flue must remain vented top and bottom, or it slowly fills with condensation, eventually making the chimney breast damp, and possibly staining it with tar residues carried through in the moisture.

If the flue backs on to an outside wall, a good way to do this at the bottom is to put an airbrick through the rear of the fireplace to the outside, and then seal up the inside, so the base of the flue is vented to the outside without the possibilities of drafts and windy flue noises inside.

Reply to
Andrew Gabriel

But that ignores the warm air that you have to allow out of the room - carrying condensation and combustion products. And the cold air that comes in to replace it. That makes it much less than 100% efficient overall.

Plus, you must have the ventilation open at all times. It could be minus something outside, you might not even be using the fire, but you are still letting warm air out/cold air in, 24/7.

Reply to
Rod

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've>> just had an old Baxi Bermuda back boiler and its associated fire

Ah, right, cheers Andrew. When we had the old Baxi Bermuda 552 back boiler, there was (and still is as we haven't done anything with it yet) a removable panel on the right-hand side of the fireplace for access to the central heating pump, which is obviously not air-tight. Do you reckon that this would be enough ventilation to prevent the formation of condensation within the flue as it's unfortunately not on an outside wall?

Reply to
John

Fair enough - but remember that the main, overriding reason for getting this particular fire is that we like the look of it. We very rarely use the fire anyway. In fact, thinking about it, its main use is on a summer's night, say about 10.30 or 11-ish when it's just gone a bit coolish - fire on for 5 or

10 minutes and it takes the chill off the room 'til we go to bed an hour or so later.
Reply to
John

I have no problem with you liking the look of it! Entirely your choice.

If the room is heated (e.g. it has a radiator on your CH), then the overall extra loss of heat over the year (by meeting the increased venitlation requirement) could be very significant. Of course, this might not be relevant in a given circumstance.

Reply to
Rod

I'm not familiar enough with back-boiler flue construction to know if that opening is likely to go through to the flue. Someone else will need to chip in.

Another place you might be able to vent the bottom of the flue to would be the sub-floor void, if you have one. Depends how much work would be involved in making an air path through to it.

As to the amount of ventilation -- I found I had one old flue sealed at the top and with an air brick at the bottom, which due to lack of any air flow path, had water streaming down the inside after 20 years like this. I cut out half a brick in the attic through to the flue, and 3 months later it had all dried out, and has stayed that way ever since. So you probably need the equivalent of no more than half a brick size vent top and bottom to keep it ventilated and dry. (Obviously, nothing needed at the top if it's not capped and sealed.)

Reply to
Andrew Gabriel

Bzzzt - wrong!

Your 100cm^2 purpose-provided ventilation is like having a brick-sized hole in the wall, so you're going to be losing heat by drawing in cold air which the fire has then got to make up for as well as warming the room.

Couldn't you just arrange a nice fireglow bulb inside it and use the central heating? ;-)

Reply to
John Stumbles

You might like the look of it but don't rely on it for heat. If you want heat from it you will need a dehumidifier to extract the heat and moisture from it before you waste it all in ventilation. If you don't ventilate enough you will have nice black mould growing.

Its like old bottle gas heaters.. 100% efficient, but only if you like living in a greenhouse. You get three things from burning gas, water, heat and CO2. A lot of the heat goes out with the ventilation needed to get rid of the water and CO2.

Reply to
dennis

The old Baxi Bermuda will have had a lined flue, and a metal terminal.

Little or no rain will come down the liner. Anyway a tiny amount of trickle ventilation up the old flue liner will do no harm.

Reply to
Ed Sirett

Hang on a minute chaps, you and Rod are taking me too literally. When I say that the flueless fire is 100% efficient, I mean the fire itself. Remember I am replacing an existing fire, not starting from scratch, so air vents, draughts, and the like are already in place and have been for years.

What I meant is that our old boiler had a Baxi GF3 Super, Outset Renewal Fire Front on it and (haven't got the exact figures to hand at this time of night but....) needed something like (for "high" setting) 5.9kW input to produce 3.6kW output - therefore not very efficient. The new fire we've just bought, again for high setting, needs 2.6kW input to give 2.6kW output - not bothered about draughts or vents - just purely what the fire itself does, so is 100% efficient.

John.

Reply to
John

We aren't - see my posting of 13.05hrs

See my reply to John Stumbles at 00.42

John

Reply to
John

I think both John and I were arguing from the point of view of an electric fire, similarly fitted, being 100% efficient (as near as dammit). And by using electric heating in this way, you would (probably) be well advised to reduce ventilation - at least with closable vents. So

*that* was my mental start point.

If the old fire (and I am just assuming that it was an "ordinary" fire as your description doesn't ring any bells with me) needed 5.9 kW to produce 3.6 kW output - well the difference is largely going up the chimney. The combustion itself is probably pretty good.

You are now effectively making your room the chimney. So recalculate as

2.6 kW gives 2.6 kW of which (guess) 800 W goes straight out of a vent. (A vent that would not exist if the room were electrically heated - as in first paragraph.) So the heating capacity of your new fire would be around 1.8 kW - around half that of your old fire. Turn your old fire down to half and the figures will be quite similar.

And, by regulation, you cannot reduce the ventilation below that required by the fire - even when it is switched off.

I do accept that this does contain assumptions - e.g. I am thinking a room in an ordinary house - so the negative effect of the permanent vent will affect the whole house heating. But I think the argument is reasonable for a lot of circumstances.

Reply to
Rod

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