A non-sealed-flue[1] gas boiler means there needs to ventilation in the room,
which is provided by air brick(s) (on the opposite wall to the gas voiler).
This tends to produce a howling gale of cold air in winter, especially when
the wind is blowing against the wall. Is there any kind of heat exchanger
that would attempt to recover some of this heat without impeding air flow
too much?

I'm guessing it wouldn't work without forced airflow (which is possible, but
complicates matters)? Or is there some kind of passive (eg convection)
solution?

What sort of airflow is required for safe combustion in the average gas
boiler?

Thanks
Theo

[1] I don't know the exact term, but it's the type of gas appliance which
operates like an open fire, in that the oxygen comes from the room, rather
than outside, but the combustion gases go up the flue.

On Thu, 06 May 2010 13:40:47 +0100, Theo Markettos wrote:

A non-sealed-flue[1] gas boiler means there needs to ventilation in the room,
which is provided by air brick(s) (on the opposite wall to the gas voiler).
This tends to produce a howling gale of cold air in winter, especially when
the wind is blowing against the wall. Is there any kind of heat exchanger
that would attempt to recover some of this heat without impeding air flow
too much?

No.

I'm guessing it wouldn't work without forced airflow (which is possible, but
complicates matters)? Or is there some kind of passive (eg convection)
solution?

Not possible. Where are you going to recover the heat from? The cold air
is coming in to replace air being burned in the appliance and going up the
flue as Carbon Dioxide and Water (as steam). There isn't a corresponding
flow of warm air out of the room, as there is with mechanical heat
recovery ventilation units.

The sensible energy-efficient approach is to replace the inefficient and
potentially-unsafe open-flued boiler with a high-efficiency room-sealed
one.

What sort of airflow is required for safe combustion in the average gas
boiler?

Approx 5cm^2 per kW of heat input to the appliance, less 7kW of the
appliance's rating (a certain amount of ventilation is assumed to be
available "adventitiously", i.e. from natural draughts). So for a 14kW
appliance you need 7 * 5 = 35cm^2.

Heating-only boilers (which heat hot water in a cylinder, rather than
instantly as a combi does) tend to be rated 10-15kW.


Thanks
Theo

[1] I don't know the exact term, but it's the type of gas appliance which
operates like an open fire, in that the oxygen comes from the room, rather
than outside, but the combustion gases go up the flue.

Open flue or conventional flue.



--
John Stumbles -- http://yaph.co.uk

Procrastinate now!

In article , YAPH
writes
On Thu, 06 May 2010 13:40:47 +0100, Theo Markettos wrote:

A non-sealed-flue[1] gas boiler means there needs to ventilation in the room,
which is provided by air brick(s) (on the opposite wall to the gas voiler).
This tends to produce a howling gale of cold air in winter, especially when
the wind is blowing against the wall. Is there any kind of heat exchanger
that would attempt to recover some of this heat without impeding air flow
too much?

[1] I don't know the exact term, but it's the type of gas appliance which
operates like an open fire, in that the oxygen comes from the room, rather
than outside, but the combustion gases go up the flue.

Open flue or conventional flue.
Often abbreviated to CF when looking for details on boiler models with
multiple flue options

I wonder if there isn't some wobble room here to provide a ventilated
cabinet for the boiler to separate it from the room?

I am thinking of ducted ventilation to the outside or ventilation from
underfloor (although I believe that ventilation (area) requirements are
higher from such sources). Likely extras might be high level ventilation
requirements (to the room) from a cabinet to release boiler heat, maybe
low level too but arguably that is being provided by the external
source.

All this dependant on current regs and the manufacturer's requirements
in the installation instructions and of course the o/ps ability to
accommodate such a construction without it looking like a dog's dinner.
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

"Theo Markettos" wrote in message
...
Is there any kind of heat exchanger
that would attempt to recover some of this heat without impeding air flow
too much?


Recover what ? .... as you mentioned the air coming in is cold ... you are
not losing heat out through the air brick .... now you are losing heat
elsewhere or no air would be drawn in.

If it is as bad as you say ... change to a room sealed boiler, a small
balanced flue model may solve your problem.

On Fri, 7 May 2010 09:43:04 +0100, Rick Hughes wrote:

Is there any kind of heat exchanger that would attempt to recover
some
of this heat without impeding air flow too much?


Recover what ? .... as you mentioned the air coming in is cold ... you
are not losing heat out through the air brick .... now you are losing
heat elsewhere or no air would be drawn in.

Quite, you can get "draught free" free flow ventilators though. Try a
google on "black hole ventilator" (other makes and models are
available).

--
Cheers
Dave.

YAPH was thinking very hard :
Not possible. Where are you going to recover the heat from? The cold air
is coming in to replace air being burned in the appliance and going up the
flue as Carbon Dioxide and Water (as steam). There isn't a corresponding
flow of warm air out of the room, as there is with mechanical heat
recovery ventilation units.

There is, but it goes up the chimney or flue.

One old solution, was to have an under-floor air vent where the air
supply came in close to the point where it was to be burned - rather
than at the back of the room, where the cold air would travel past the
room's occupants.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Harry Bloomfield wrote:

One old solution, was to have an under-floor air vent where the air
supply came in close to the point where it was to be burned - rather
than at the back of the room, where the cold air would travel past the
room's occupants.

Indeed so. My parents used to have a pair of gray plastic
"Tele-vents" in the floor either side of a coal fire. When pulled
up, they allowed a gale to blow through, rather than howl across
the room from under the door.

Chris
--
Chris J Dixon Nottingham UK


Have dancing shoes, will ceilidh.

YAPH wrote:
Not possible. Where are you going to recover the heat from? The cold air
is coming in to replace air being burned in the appliance and going up the
flue as Carbon Dioxide and Water (as steam). There isn't a corresponding
flow of warm air out of the room, as there is with mechanical heat
recovery ventilation units.

Ah, good point.

The sensible energy-efficient approach is to replace the inefficient and
potentially-unsafe open-flued boiler with a high-efficiency room-sealed
one.

This isn't practical in this situation, much though it's obviously the best
option.

The main thing is to reduce draughts while not interfering with combustion.
Does such an arrangement draw in cold air by convection? So would, for
example, a louvred path be OK because the combustion causes
lower pressure in the room that would suck in fresh air? Or would the
boiler happily churn out CO before it causes a significant pressure
difference?

What sort of airflow is required for safe combustion in the average gas
boiler?

Approx 5cm^2 per kW of heat input to the appliance, less 7kW of the
appliance's rating (a certain amount of ventilation is assumed to be
available "adventitiously", i.e. from natural draughts). So for a 14kW
appliance you need 7 * 5 = 35cm^2.

I'm a bit puzzled by the units. That means a grille 7cm x 5cm, presumably?
But what's the amount of air input you need to the boiler (ie in cm^3 per
second)?

Theo

On Sat, 08 May 2010 09:36:46 +0100, Theo Markettos wrote:

YAPH wrote:

The sensible energy-efficient approach is to replace the inefficient
and potentially-unsafe open-flued boiler with a high-efficiency
room-sealed one.

This isn't practical in this situation, much though it's obviously the
best option.

It will be necessary in due course when the existing unit packs up.

The main thing is to reduce draughts while not interfering with
combustion. Does such an arrangement draw in cold air by convection? So
would, for example, a louvred path be OK because the combustion causes
lower pressure in the room that would suck in fresh air? Or would the
boiler happily churn out CO before it causes a significant pressure
difference?

The important criterion is that the air vent be unobstructed by e.g. fly
grilles. Commercially-available vents for the inside wall generally have
louvres, but that won't do much to help if there's a stiff breeze blowing.
A properly installed appliance should have its air supply arranged so as
*not* to produce an unpleasant draught across living areas, e.g. by being
ducted under the floor to come up beside the appliance (precisely because
it may encourage occupants to block it up) but this is only a
recommendation rather than a requirement of the British Standard and more
honoured in the breach.

I'm a bit puzzled by the units. That means a grille 7cm x 5cm,
presumably? But what's the amount of air input you need to the boiler
(ie in cm^3 per second)?

The free area of ventilation is what's specified in the gas installation
regs. The volume rate is something you (or someone else with a better
recollection of school physics & chemistry than me :-)) can work out.



--
John Stumbles -- http://yaph.co.uk

I've got nothing against racists - I just wouldn't want my daughter to marry one