UK gas boiler (furnace) efficiency - or lack of it.

[Zinjanthropos]

I used to set up conversion burners on old boilers. Biggest problem was too much air leaking into the combustion chamber. A tub, maybe more of furnace of cement and flue gas analyzer required. But if you couldn’t plug leakage spots or find them all then more air better than not enuf. Improve combustion by plugging openings/cracks.

Sometimes a brick was placed to slow down draft hood air intake. The analyzer was able to calculate efficiency also. Ideally we hoped for 80% I believe back then and no CO. Otherwise the boiler was toast. Red tag and disconnect….I worked for the nat gas distributor. I’d do 8 a day if all went well. Perhaps govt can subsidize a check of the old boilers and maybe an incentive for newer appliance?

[confused2]

Perhaps govt can subsidize a check of the old boilers and maybe an incentive for newer appliance?

The boiler and thermostat I'm contemplating scrapping (to save money) are both current models - the thermostat first appeared about 2 years ago and isn't exactly cheap. Newer appliances can be worse than the ones they replace. The boilers are reliable and have 90% efficient written on them so why shouldn't they be a popular replacement boiler?

[Zinjanthropos]

Perhaps govt can subsidize a check of the old boilers and maybe an incentive for newer appliance?

The boiler and thermostat I'm contemplating scrapping (to save money) are both current models - the thermostat first appeared about 2 years ago and isn't exactly cheap. Newer appliances can be worse than the ones they replace. The boilers are reliable and have 90% efficient written on them so why shouldn't they be a popular replacement boiler?

All the old boilers I used to work on are gone, from this geographical area anyways. My ex-employer, the gas distributor, offered an incentive for replacement. No gas distributor wants a death by explosion or CO poisoning on their docket. Would you supply gas to an old boiler knowing it could kill? Nope, and neither would they.

I doubt the poor people stuck with the old boilers you mentioned can’t afford a new one.

[confused2]

Perhaps govt can subsidize a check of the old boilers and maybe an incentive for newer appliance?

The boiler and thermostat I'm contemplating scrapping (to save money) are both current models - the thermostat first appeared about 2 years ago and isn't exactly cheap. Newer appliances can be worse than the ones they replace. The boilers are reliable and have 90% efficient written on them so why shouldn't they be a popular replacement boiler?

All the old boilers I used to work on are gone, from this geographical area anyways. My ex-employer, the gas distributor, offered an incentive for replacement. No gas distributor wants a death by explosion or CO poisoning on their docket. Would you supply gas to an old boiler knowing it could kill? Nope, and neither would they.

I doubt the poor people stuck with the old boilers you mentioned can’t afford a new one.

Fair comment. I am annoyed to find that I have wasted £2,000 ($2,010) on the assumption that a recent product [edit design] would be better than an earlier one and ir isn't.

[Zinjanthropos]

. Fair comment. I am annoyed to find that I have wasted £2,000 ($2,010) on the assumption that a recent product [edit design] would be better than an earlier one and ir isn't.

Hold that thought until you’ve seen a gravity furnace in operation. A metal octopus with no moving parts, occupying your basement and heating the air in your house. A museum piece you might call a low efficiency furnace…lol. Worked on the simple principle of cold air falling and hot air rising.

You’d be surprised C2 to see just how many houses there are out there that have cold air returns at ceiling level. Nothing like having heated air blown into a room and immediately returned to the furnace. Meanwhile most heating grates are at floor level. Cold air returns should be at floor level, don’t cover or block them with rugs or furniture. A lot of complaints I used to deal with were people who’s ankles/feet felt cold air rushing over them when furnace was running….duh. It’s what you should be feeling if it’s working properly…put on a pair of socks…lol Gas equipment probably the least understood appliances in a household and that is a bigger problem than designing more efficient devices. Train the owner first on how they work.

[confused2]

Let's say we have a furnace that uses gas (measured at the gas meter) at 30,000 BTU/hr.
At 90% efficiency we get a useful heat output of 27,000 BTU/hr

Where does the lost 10% go?
Assuming (normally true) complete combustion of the gas the lost 10% goes out through the flue - if it went anywhere else we'd have included it as 'useful'.

CH4 + 2O2 -> CO2 + 2H2O + heat
gas + oxygen -> CO2 + water + heat

In reality air is only about 20% oxygen (80% nitrogen) so for complete combustion the minimum amount of air required is about 10 cu ft of air for every 1 cu ft of gas.

In a real furnace we expect about 10% CO2 at the flue which fits with 90% of the air that goes into a furnace comes out warmer but otherwise unchanged.

In a rough and ready fashion ..
We can increase furnace efficiency from about 80% to 90% by reducing the flue temperature enough to condense out the water formed as the gas burns. Once at 90% efficiency where are we losing 10% of the energy we're paying so much for? Could we be paying for the hot air that comes out of the flue which is 90% the same as when it went in except now it is hot?

[Zinjanthropos]

Primarily flue gases for lost efficiency.

Design a burner that doesn’t heat up. A heat exchanger that doesn’t absorb any. A furnace casing that remains cold during operation. Ductwork & water lines that resist heat. Never going to be 100%. Go geothermal.

Maybe the quantum furnace one furnace superpositioned in each room. Virtual heat

[confused2]

Good. The furnace takes in air at (say) 32F and sends it out at 120F and this is the 3,000 BTU 'lost heat'.
Water is returning to the furnace at 120F
We have just the one 3,000 BTU radiator connected to the furnace.
It looks like the furnace should burn gas for (say) 30 seconds and wait to cool for (say) 300 seconds .. otherwise the water in the furnace would boil.

During the cooling phase the combustion fan and the water pump continue to run

Now comes the conceptually difficult bit where either I am wrong or 'something'..
We paid a lot of money for a very efficient heat exchanger..
Instead of hot gas (mostly air) heating the water the hot water now heats the air going through the furnace with the same 90% efficiency that is written on the back of the furnace.
So the air comes out of the furnace at (about) 120F which we found earlier was a 3,000 BTU/hr loss.
When the water temperature falls below (say) 115F the boiler burns gas again to heat the water back up to 120F
So the furnace loses heat (about 3,000 BTU) even when it isn't burning gas.
This isn't quantum mechanics .. am I wrong about this?
Basically a 30,000 BTU boiler heating (waste) exhaust at 3,000 BTU and 1 radiator at 3,000 BTU .. overall 50% efficiency.

[Zinjanthropos]

Good. The furnace takes in air at (say) 32F and sends it out at 120F and this is the 3,000 BTU 'lost heat'.
Water is returning to the furnace at 120F
We have just the one 3,000 BTU radiator connected to the furnace.
It looks like the furnace should burn gas for (say)  30 seconds and wait to cool for (say) 300 seconds .. otherwise the water in the furnace would boil.

During the cooling phase the combustion fan and the water pump continue to run

Now comes the conceptually difficult bit where either I am wrong or 'something'..
We paid a lot of money for a very efficient heat exchanger..
Instead of hot gas (mostly air) heating the water the hot water now heats the air going through the furnace with the same 90% efficiency that is written on the back of the furnace.
So the air comes out of the furnace at (about) 120F which we found earlier was a 3,000 BTU/hr loss.
When the water temperature falls below (say) 115F the boiler burns gas again to heat the water back up to 120F
So the furnace loses heat (about 3,000 BTU) even when it isn't burning gas.
This isn't quantum mechanics .. am I wrong about this?
Basically a 30,000 BTU boiler heating (waste)  exhaust at 3,000 BTU and 1 radiator at 3,000 BTU .. overall 50% efficiency.

Are you talking about the unit itself or overall performance (system). Even the Suns efficiency sucks for Earth as most of the heat goes into space. ...a good thing

[confused2]

Are you talking about the unit itself or overall performance (system).

I'm talking about what happens when you leave the water pump and combustion fan running when not burning gas for actual heating.
The system loses heat 3,000 BTU up the chimney and 3,000 BTU to the radiator the whole time the thermostat calls for heat.
To get 90% efficiency you'd need to cut out that 3,000 BTU chimney loss while the furnace isn't actually burning gas.
For some reason I seem to be the only person on the planet that sees that.

You have input 30,000 BTU, Output 27,000 BTU .. 3,000 BTU up the chimney when the water is up to temperature - it's written on the box.