Balanced Flue Gas Fire Question

[GeddyMortgage]

if they check it out and say it’s all working as intended etc. then I may look to swap it out for something larger and a diff brand.

I saw this thing from Gazco called the “Studio 3” but it’s the same thing again…. 8.4kw output…. 10.1kw input… 92% efficiency.

Though I don’t know if that 10.1kw is Hs or Hi…

 

[JonathanM]

It's all a bit confusing. I know more about boiler efficiencies and how they are calculated. I've never looked at gas fires before. I actually had no idea they were anywhere near this efficient, I would have guessed about 70%.

 

[GeddyMortgage]

I’m wondering if the difference between the input and output only partly influences the efficiency.

it definitely looks like it’s part of the calculation. Like on the image below the lower efficiency conventional flue types have a bigger difference between in and output. But still don’t add up. So there must be another factor that affects the calculation?

To be fair I don’t think you’re far off in real terms. They’re all like 75% based on in and output

 

[JonathanM]

The figures are very confusing. These people seem to know quite a bit about it. They have a number of articles on the website about modern gas fire improvements and mention a British Standard for calculating efficiency BS 7977-1:2009

Are Gas Fires Efficient? | Charlton & Jenrick

Discover the reasons why gas fires are so efficient and how they have improved in design and efficiency in recent years.

www.charltonandjenrick.co.uk

 

[Harry Bloomfield]

It's all a bit confusing. I know more about boiler efficiencies and how they are calculated. I've never looked at gas fires before. I actually had no idea they were anywhere near this efficient, I would have guessed about 70%.

Flame effect fires, have always offered very poor efficiency, I have heard of lots of people buying them, realising how inefficient/how little heat they produce, and swapping them for something better. My guess is that efficiency figure, must be measured at the most efficient setting.

 

[GeddyMortgage]

“Flame effect” as in electric?

When you say better, what are they swapping out for? This was one of the largest kw gas fires I could find.

 

[JonathanM]

“Flame effect” as in electric?

I think Harry means living flame gas fires, like yours.

Flame effect fires, have always offered very poor efficiency, I have heard of lots of people buying them, realising how inefficient/how little heat they produce, and swapping them for something better. My guess is that efficiency figure, must be measured at the most efficient setting.

The articles seems to say that the efficiency has improved enormously, from 20% in the 1970s to 50% at the end of the 1980s, and now sometimes 85%+. Having a balanced flue, rather than a chimney seems to help. And then there's lots of changes to the firebox. The glass front also seems to make a big improvement.

 

[GeddyMortgage]

Sure, but is that sealed glass stopping the heat coming into the room? Efficiency is sort of secondary to me… more concerned about the outright heat right now! I could lose 10% efficiency happily if it was dead hot

 

[JonathanM]

Is it the primary form of heating in that room? Earlier, I found this thread on MSE, where the exchanges with rustyboy21, who sells gas fires, are very interesting. He seems to be saying that glass fronted heat by convection mainly. I have no idea whether that is true. The thread is almost ten years old now, but worth a read. I'm sure you will find more recent with Google. It looks like open fronted are still only about 55% to 65% efficient, glass fronted with chimney are 75%+ and glass fronted balanced flue are 85%+.

Glass fronted gas fire or open?

I'm about to replace my fireplace and gas fire. The gas fire currently there is an open living flame fire.

forums.moneysavingexpert.com

 

[GeddyMortgage]

I’ll take a look.

By convection do you mean, heat radiating from the flue? I’d say that is true if so. The little vents they put in the faux breast pump out a lot of heat. I wish I’d had them fitted much lower to be honest. With heat naturally rising I assume I’d “feel” it more.

 

[JonathanM]

I’ll take a look.

By convection do you mean, heat radiating from the flue? I’d say that is true if so. The little vents they put in the faux breast pump out a lot of heat. I wish I’d had them fitted much lower to be honest. With heat naturally rising I assume I’d “feel” it more.

To be honest, I don't actually know what he is referring to. And I think maybe that link predates balanced flue fires, so it might not be that useful after all.

If you stand close to the fire, can you feel the heat, like with an open fire?

Is there any way to tell whether the glass gets really hot without burning yourself?

 

[GeddyMortgage]

You can, hard to compare to an open fire without feeling them side by side, but they do give off heat sure. The glass is too hot to touch ofcourse also.

But i too think with a glass fronted conventional flue, they draw air in through the front rather than through the flue as is the case with balanced flue. So where conventional draw air in through the front, I imagine heat comes out there also.

 

[JonathanM]

I am trying to think of the physical principles involved. If the glass is very hot, say 200C, then won't that act like a central heating "radiator"? and cause some of the heat to be convected (upward) from the glass outer surface.

But that aside, what is the main principle on which these type of fires work? Is it that the flame heats the logs and the rest of the components of the fire bed (to say, 1000C) and this in turn radiates heat as infared radiation? and most of this infrared is short enough wavelength to pass through the glass without actually heating it?

 

[GeddyMortgage]

I thought so too, and I had a question for the installer asking - should the placement of the decorative logs etc… go through the flames? So they heat up etc, but he said no.

Could do with a second opinion on that, as thermodynamically that makes sense to me…

 

[gas112]

I’ll take a look.

By convection do you mean, heat radiating from the flue? I’d say that is true if so. The little vents they put in the faux breast pump out a lot of heat. I wish I’d had them fitted much lower to be honest. With heat naturally rising I assume I’d “feel” it more.

View attachment 341856

is that an opening velux window if so that flue terminal looks far too close the usual distance is 2metres away when below velux