gas fires that have no flue

-snip-

Thanks for that. I've never seen watts used to measure heat except in electric heaters. Might be our 'common language' - or it might just be that I haven't spent a lot of time reading about heat lately.

Jim

Reply to
Jim Elbrecht
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I guessed that alt.home.repair was mainly used in America, the original post was cross posted with free.uk.diy.home.

Gas ovens, gas hobs, gas boilers all seem to be measured in kW in the UK.

The flueless gas fires seem more to be for display than actual heating over here. krw's 8kW fire looks like it is meant to actually heat things up and not just look pretty.

Adam

Reply to
ARWadsworth

Over here in the US we use a rating you probably have never heard of, BTU, British Thermal Unit. Kw, but you guys are not metric, driving on the Right side is Right.

Reply to
ransley

That's pretty much what I suspected. ;-)

Yes, both "vented" and "vent-free" gas logs are available. The vent-free variety tend to have a higher output and are used for heating. The vented logs are more or less for decoration, since much of the heat escapes up the flue.

We use heat pumps for central heat. The idea of the gas fireplace logs is for auxiliary heat for the few nights where it's really too cold for the heat pumps to operate well (not enough resistive heat to maintain temperature, either). We should also be able to turn the temperature in the house down a few degrees because the gas will help recovery (heat pumps suck).

Reply to
krw

The problem with a flueless gas fire is...

- Ventilation requirements likely exceed the heat output capability

- Water output is high, not unlike an LPG bottle radiant heater

In the UK there are Balanced Flue flame effect fires.

- These simply require an outside wall

- Drill a hole, fit a coaxial flue

- Air pulled in from outside, combustion products out

It would be interesting to compare a flueless gas fire efficiency (with BG 10x10cm free air flow vent) to an electric version. Gas is abour 3p, Electric peak is about 10p (UK).

I recall Gas Inset DFE Fires can be below 35% efficient and any heat up the open flue will draw more cold air through the house so are probably 25-20% efficient in most cases. That means they are as or more expensive than an "Electric DFE" - better to get an oil radiator or fan heater and a TFT panel with flickering fire video looping on it.

Reply to
js.b1

I'm not understanding this. Maybe it is our 'common language'. Is 'flueless' the same as 'ventless'? In the US a ventless has no requirement for outside air.

My 30K BTU heater has never steamed up any windows. A pot of spaghetti on the stove puts out more moisture.

For me, the moisture that is added by an LPG fire is welcome- as it is a struggle to keep the humdity as high as 38 in my NE US winters.

A ventless fire- there are wall heaters and freestanding stoves, as well as 'logs' that go in fireplaces- in the US just needs a gas line run to it. Combustion air is provided by the natural infiltration that all houses have. There is a safety switch that should turn the gas off is there is not enough oxygen for combustion.

This year- my ventless is slightly more expensive than electric. [but cheaper than my oil by about 25%] Up until a couple years ago it was cheaper than the electric.

I used 100% efficiency for electric and my ventless propane-- and 75 % for my oil furnace. It tests at 85% at the flue, and I allow for a bit lost in the ducts.

Although we both seem to have a different idea of ventless/flueless - we both agree that anything with a chimney in a living area is a losing proposition.

Jim

Reply to
Jim Elbrecht

Some info here

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and the report that it links to.

Adam

Reply to
ARWadsworth

I imagine so, however secondary ventilation is often needed in the uk. A flueless gas fire in the UK has no flue or vent but there is a reqirement for a ventilation hole elsewhere in the room to allow fresh air in.

Of course. You are boiling water on the stove and creating extra moisure. Even lighting the stove with no pot on will create some moisture as a by product of the burning process.

Many house in the UK suffer from damp and extra moisture is not welcome. New build houses in the UK are often air presure tested and need to meet specific targets to stop the natural ingress of air.

A little bit of water between us makes a big difference to a common language.

Adam

Reply to
ARWadsworth

Nonsense.

In the winter water is goodness. It's not all *that* much water, anyway.

We have those too; ugly. Our fireplace is on an interior wall anyway.

Which is about 1/2 our cost. Electric fireplaces are even uglier. If I wanted to heat with resistive electric heaters I'd ditch the heat pumps (an incredibly *dumb* idea).

How are you measuring "efficiency"? They certainly combust more than

65% of the propane.
Reply to
krw

From memory it is roughly that 22.4 litres - which is a bit under a cubic foot - of methane (natural gas) gives 36g of water which is about an ounce and a bit. So a fair bit of water. I would look at my gas bill and tell you how many kWh per cubic metre methane is, but I've lost it.

Reply to
Chewbacca

In the case of propane:

C3H8 + 5(O2) => 3(CO2) + 4(H2O)

If I've done my arithmetic properly... Water vapor output is 4x the propane input by volume or about 25% more by weight. A gallon of propane weighs something like five pounds so, if I've done my numbers right, it'll put out a little less than a gallon of water. A gallon is 93kBTU, so a bit under three hours on a 37kBTU (my 8kW, from before) logs. A extra gallon of water would be quite welcome in most houses in the heating season.

Reply to
krw

No & Yes - it depends on house design:

2008 - near air tight, well insulated. 1950 - air sieve, uninsulated, 1-2 open flue chimney.

USA housing stock differs greatly from UK.

2008 house is a near air tight box.

- Air tight = few Air Changes per Hour (ACH)

- Adding a 4in*4in vent doesn't make ACH rocket

- So comfort impact is limited

Cited H&S study found the vent didn't affect temps much. That is as expected, 2008 house has little heat loss & has

*restricted* ACH.

1950 house is full of huge holes.

- Air sieve = huge Air Changes per Hour

- 1-2 open flue chimney with convection column from room heat & wind action.

- Adding a 4in*4in vent will make ACH rocket

- So comfort impact is enormous

Example.

1 - 1950s living area, flue blocked by plywood.

- Heat calc: 440W required for 21oC.

- Heat test: 500W heater maintained 22oC.

2 - 1950s living area, flue with outset gas fire turned OFF.

- Heat calc: 750W required for 21oC based on ACH guess.

- Heat test: 1440W heater maintained 19.5oC.

3 - 1950s living area, open flue.

- Heat calc: 1000W required for 21oC based on ACH guess.

- Heat test: 2000W could not raise temp 15oC.

UK housing is closer to 1950 than 2008. Wall hung flueless fires work well in modern air tight construction. HSE test indicates they DO thermally work in modern air tight construction, but the problem is 1) CO2 concentration 2) a poor burner hidden by a catalyst.

UK Inset Decorative Flame Effect Fire:

- Inset DFE fire sits below an *open flue*.

- Mimimal fire output radiates into the room.

- Most fire output convects up the chimney.

- Open chimney draw sucks the room cold.

- Net result is you burn 6-8kW for 2kW into room.

- Complaint usually "frozen & cold ankles re draughts".

Nothing to do with the burner efficiency.

Inset DFE efficiency typically quoted 28-38%.

- UK thermal losses can be high re minimal Floor Wall Loft insulation.

- UK ventilation can be high re numerous house wall vents.

- Stick an 8kW flame below an open flue and all the heat goes up it

With older UK house thermal losses and often numerous 9in*6in ventilators, sticking a DFE fire below an open flue creates an immensely powerful heat pump up the chimney. Real world figures can be as low as 15%, so even with 8kW input people can't get warm because the draught sucks the room cold or entire house cold yet high running costs.

This is one area where UK v USA can differ enormously re installed housing construction.

Reply to
js.b1

In the UK the opposite is preferable.

Kitchen:

- 75m3/hr extractor over a cooker/hob

- 150m3/hr extractor if say a wall fan

Bathroom:

- Similar water extraction required

UK houses very quickly suffer from damp & condensation. If you try to heat an older house via an LPG portable heater the airflow requirements for the burner and to avoid condensation will almost negate the heating effect (ie, you will need huge amounts of LPG to compensate making the seemingly cheap heating very much more expensive).

UK construction:

- Double solid brick or similar (

Reply to
js.b1

Interesting report.

They did the test on modern housing, no open flue or large number of vents, because they were specifically interested in combustion safety. The vent presence/no-presence did not affect temperatures much because the vent could not supply an open flue which will draw even without a fire due to convection (even solar :-)

For older housing the Open Flue when combined with 4in*4in free area vent can be "quite a draughty combination".

Modern houses DO have a wonderful luxury of high insulation level. Wall of U =3D 0.35 is so much different to U =3D 2.11 and the wood-inner- leaf also tends to mean very rapid heat up (problem then becomes enough thermal mass in the room, but fast warmup is great for working people arriving home as it saves on background non-resident heating requirements).

Reply to
js.b1

I suspect the closest we come in the US to similar conditions would be our Northwest coast. We started in the US in the 70s to make super-tight houses, and I believe that theory has fallen into dis-favor because the indoor pollution was deemed more dangerous than the monetary gains. [I might be all wet now, I haven't been in that business for 30 years, so I don't read many current trade books.]

I note on air exchanges on this page from 1997- that ASHRAE [American Society of Heating, Refrigerating and Air-Conditioning Engineers] recommended a minimum of .35 air exchanges per hour in residential construction-- but in practice most houses had 1.1.

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Do you know how that squares with UK housing?

Indeed. This is one area where it would have saved the OP some misleading info if they had named their continent, at least.

Jim

Reply to
Jim Elbrecht

Living Room generally 2 ACH. Living Room w/Open Flue can be 3.5-5.5 ACH.

Open Flue can really stuff up the figures for UK GCH (wet) radiator sizing, you can go from 440W to 1800W.

Reply to
js.b1

Even in Alabama it's so dry in the Winters that many run humidifiers. Anytime you heat air the RH drops. Heat air 50 degrees and lizard skin isn't unusual.

Water extraction or ventilation? That's significant air exchange right there.

That's not the point. Heating air reduces its RH. It's not unusual to have an interior RH under 20%.

Reply to
krw

This gives some idea on the UK recommended air changes

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We tend to rely on mechanical ventilation and not air conditioning. However I have noticed more households are installing air conditioning. (You have to realise that air con in cars has only just become the norm over here)

The daft thing is, we now make houses air tight and then add trickle vents to the windows or fans to certain rooms to allow ventilation.

Adam

Reply to
ARWadsworth

Humidity below 0oC collapses.

UK winter consists of continual cycle of freeze (-4oC, low humidity) & thaw (+4oC, high humidity). USA winter can be "goes below 0oC and stays below 0oC".

UK 1950s house with moderate ACH & no central heating.

- Humidity inside will be very high, most wood will have some cupping, paper & cardboard will be "soft", leave a block of A4 paper out and run it through a laser printer and it will come out as unusable "wood curls".

- Brick uninsulated walls are typically near the dew point, condensation with any moisture input is very common

UK 2000s house with few ACH & (wet) radiator central heating.

- Humidity inside will be very low, everything will be "biscuit dry"

- Brick uninsulated walls are typically above the dew point, but moisture buildup due to few ACH is not removed which can cause condensation just the same

The big moisture input with (wet) radiator central heating is of course people drying washing on radiators :-) The few ACH means that moisture just builds up, eventually eliminated

- but in the mean time the humdity can cycle from very low levels to very high. It is this that can cause furniture problems are localised humidity.

Yes heating air does reduce its RH. However with ACH of 5-8 this will just not happen - you will get wild swings in humidity and localised high/low humidity.

USA tends to use recirculating ducted warm air heating - good for managing humidity and permitting multiple heat input choices (heat pump, electric backup, gas/oil/wood... dodgy DIY nuclear) and is free of water leak/freeze risk from wet radiator systems.

A lot of the UK housing stock has followed a peculiar route:

- Uninsulated brick walls + Uninsulated loft (12.5mm sheetrock to sub- zero loft) + Uninsulated floors

- Typically 4-7-12 wall vents, some of which restricted in winter

- Then fit Double Glazing believing 50% of all heat loss is through windows - it is not! :-)

- Wet (radiator) central heating is then added to *brute-force* the house warm

- Cold uninsulated walls & ceilings create high heat loss causing plunging cold draughts

- Open flue often have a radiant gas fire in it, which sucks heated air up the chimney, pulling in very damp outside air

- Wet (radiator) central heating then brute-force heats this drawn in air to compensate

It is a quite amusing "someone actually planned this?" system. Getting rid of open-flue is good, but people do like a radiant heat source.

Reply to
js.b1

With *HIGH AIR CHANGES PER HOUR* the OUTSIDE humidity will DIRECTLY affect INTERIOR humidity if there is *INSUFFICIENT* heating.

UK house with ACH 5+ from 8-12 vents and 2 gas fire open flue chimney:

- 2 open flue chimney draught SUCK in damp air ALL OVER THE HOUSE.

- Humidity in the 2 gas fire heated rooms is LOW, temps 21oC.

- Humidity in the UNHEATED rest of house is HIGH, temps 16-12oC.

UK houses with LIMITED heating and HIGH 5+ ACH are *DAMP*.

UK houses with WHOLE-HOUSE heating are NOT damp. UK houses with WHOLE-HOUSE heating CAN become damp if people dry wet washing on radiators and stuff up every vent to reduce ACH

Reply to
js.b1

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