Hypothetical Q - reconnecting to balanced flue

[Terry Fields]

SWMBO wants to move house, and has found a really nice one she likes the look of. It appears to have been 'done up' really well, although it has downlighters everywhere - nine in the conservatory alone (gasp).

The question concerns the fire in the lounge - it currently has an electric 'contemporary' fire, but goes on to say 'Gas point and balanced flue still installed if needed'. I like the idea of a 'living flame' gas fire rather than an electric one, but would it be acceptable, and possible, to fit such a fire using the balanced flue, or would some new BR or Elfin Safety intrude here at great expense?

TIA

[Andrew Gabriel]

"balanced flue still installed if needed" doesn't make any sense; a balanced flue is part of an appliance, and comes with it. If they left an old flue behind, it won't be any use.

There were balanced flue flame gas fires (haven't looked in a decade now). They have the flames behind a glass front, sealed from the room. Like any decorative real flame gas fire, they're horribly inefficient.

[Davey]

There could be another reason why they took the gas fire out. I know we replaced our gas fire with an electric one as it was the only way we could finally sort the problem of a freezing cold draught coming into the living room via the chimney flue. I have known of people suffering cold draught problems with balanced flue gas fires also.

Also, although electric fires cost more to run, they are 100% efficient, whereas gas fires are nowhere near that. We only use ours a handul of times each year, so the cost of running is negligible.

[Rod]

But a balanced flue that allowed a freezing cold draught into the room would be rather badly installed. Wouldn't it?

[Davey]

With the prevailing wind blowing directly at the flue it brought in a cold draught. That's what I was told and there's no reason for the bloke to have lied.

[js.b1]

A balanced flue is *room sealed*, that is the whole point.

Balanced flue has inner & outer tube, IIRC...

- Inner allows air to enter for combustion ONLY

- Outer allows heated combustion products out ONLY

The only draught would be room convective draught caused by air flowing over the heat exchanger.

Class-1 chimney gas fire is conversely very different.

- Some are only 45-55% efficient (some go 72%+)

- Thus 28-55% of their heat goes up the chimney

- Air is drawn through through the house via house vents

- Thus they can cause a howling draught under a door

The most common cause of a howling draught is a full bore chimney pot without rain guard, being sucked by the prevailing wind, combined with the huge thermal mass of the chimney length. That draught can spin a newspaper from front to back without difficulty if placed near a doorway and reduces efficiency yet further - it is how a gas fire can "suck a house cold".

The often forgotten trick with open hearth fires or gas fires when out is that they STILL suck air all night long, that thermal mass & prevailing wind can combine to "suck the house cold". Stick a sausage outside the relevent door when going to bed, you may find the house is significantly warmer.

This is why some people end up with Class-1 flame-effect or gas-fires AND central heating which "fight one another", the central heating is having to preheat the air so as to avoid draughts which vanish up the chimney. A door sausage can save =A350/yr and avoid such problems - BUT there must still be sufficient air for combustion (just some chimney draw like an 9" square extractor on maximum without a fire).

So any "draught" was due to convective effects across the balanced flue fire's heat exchanger, or it was a class-1 flue type fire (using chimney).