Balanced Flue Gas Fire Question

[polesapart]

Gas is being burnt @ 8 or 9 kW

where's that heat going? Radiant to the room, convective within the plasterboarded cavity with some convection/radiation eventually to the room as things warm up and lastly chimney losses.

I'd be hard put to it to measure and disentangle these three.

 

[GeddyMortgage]

So ran it for 3hrs tonight, checked the meter on the hour, every hour, the fire if nothing else is consistent. But the figure has thrown another layer of confusion.

It was using, on the nose, 0.84 m3 per hour. Which would be somewhere in the region of 9.0-9.4 kw per hour. Though on the manual for the fire it states 7.8kw input, How or why should be drawing so much more than its max input?

So this was an error, the input for this fire is not 7.8kw. Someone from the shop had written 7.8kw on the install sheet, but when you look at the manual it does clearly say 8.7 kw input (Hi) 9.7kw input (HS)....

What is the difference between Hi & HS?

Either way, atleast we know now atleast the gas feed is fine, consistent and the fire is accurately drawing its max..ish.

 

[GeddyMortgage]

Gas is being burnt @ 8 or 9 kW

where's that heat going? Radiant to the room, convective within the plasterboarded cavity with some convection/radiation eventually to the room as things warm up and lastly chimney losses.

I'd be hard put to it to measure and disentangle these three.

Yes fair comment, the installer came back today to have a look, he did point out that those vents in the faux chimney breast are pumping out a serious amount of heat that you wouldn't really get on a conventional flu. He is right to be fair, but i wonder if that bumps up the efficiency on the fire! as 9.7kw input and 7.5kw output doesnt seem like 94% efficient

 

[Agile]

It may be part of the design but the flames look surprisingly yellow to me.

 

[GeddyMortgage]

It may be part of the design but the flames look surprisingly yellow to me.

There is an adjustment for that. They’re sending some one from DRU to come take a look. Will see what they say.

 

[JonathanM]

but when you look at the manual it does clearly say 8.7 kw input (Hi) 9.7kw input (HS)....

What is the difference between Hi & HS?

I think Hs is gross and Hi is net. They are always 11% different. It's to do with the amount of heat which is lost through the flue in the water vapour.

 

[GeddyMortgage]

I think Hs is gross and Hi is net. They are always 11% different. It's to do with the amount of heat which is lost through the flue in the water vapour.

Nice, so the higher of the two is what we see at the meter right?

 

[JonathanM]

Nice, so the higher of the two is what we see at the meter right?

That is my understanding. I believe the metering of kWh of gas used is based on the gross calorific value.

 

[GeddyMortgage]

I wonder which the fire manufacturers quote. Lower “looks” better I guess

 

[JonathanM]

I wonder which the fire manufacturers quote. Lower “looks” better I guess

Your table shows "Useful Efficiency" based on "NCV". That is net calorific value. If it was based on gross calorific value, the efficiency would be about 10% less.

 

[GeddyMortgage]

Your table shows "Useful Efficiency" based on "NCV". That is net calorific value. If it was based on gross calorific value, the efficiency would be about 10% less.

And there in lies my confusion. Even if you take the lower input value, of 8.7kw… the output of 7.5kw, isn’t 94% of that.

So how can this be advertised as a 94% efficient fire? 94% of what?

 

[JonathanM]

And there in lies my confusion. Even if you take the lower input value, of 8.7kw… the output of 7.5kw, isn’t 94% of that.

So how can this be advertised as a 94% efficient fire? 94% of what?

I was wondering the same myself! Are there any more efficiency figures?

 

[GeddyMortgage]

I was wondering the same myself! Are there any more efficiency figures?

Ours is the “g20” natural gas

 

[JonathanM]

I can't see anything obvious which would explain it. If you get the answer, can you post it!

 

[GeddyMortgage]

Certainly, I’m quite keen to know. We paid a lot for this fire…