New boiler has resulted in increased Gas usage

turbofan · 5 Dec 2008

sounds like your property is heating up quicker and looseing heat even quicker through cavity walls.
so the new higher output boiler is working hard to maintain an even temperature and burning for a longer time period.
turn down boiler thermostat.
your measurements of units is not an accurate way of calculation.

bmxboy · 5 Dec 2008

Today I have turned down the boiler themo by 1 notch and the room thermo to 20 degrees and will monitor the usgae over the next couple of days.

[your measurements of units is not an accurate way of calculation.]

It was the easiest way rahther than converting to KWH

bmxboy · 8 Dec 2008

After turning down the boiler thermostat a couple of notches and adjusting the TRVs down on the warmest rooms (kitchen, bathroom, study, dining room) and it still has been very cold in the toon over the weekend, surprisingly the amount of Gas usage has fallen significantly, from 5 units to 3.5 units. This is now very reasonable as the heating is on for 24hrs per day.
Thanks for all your advice.

D_Hailsham · 8 Dec 2008

bmxboy said:
Unsure what KWH the old boiler was, it was an apollo fanfare s.

The largest Apollo Fanfare is only 14.7kW, so a 37kW combi boiler will be more than adequate. Why did you agree to such a high output combi? Do you have a large house with several baths and showers running at the same time?

The installer should have set the max output for CH to meet your house requirements; obviously he has not done this.

bmxboy · 9 Dec 2008

D_Hailsham";p="1076878 said:
bmxboy said:

Why did you agree to such a high output combi? .

Click to expand...

The boiler guy suggested a smaller boiler but since the new boilers are self modulating they shouldn't have any bearing on gas usage.
Most importantly I will be extending the house maybe in a year or two so the bigger boiler will serve it's purpose.

Madmog · 9 Dec 2008

I would say you are doing fairly well to be using only five units a day if your system is running 24 hours. Would anyone agree? We have our heating on approx four hours a day and use approx 4 units which I think equates to about 40kw.

tonybhoy · 9 Dec 2008

[quote="D_Hailsham";
The installer should have set the max output for CH to meet your house requirements; obviously he has not done this.[/quote]

Boiler is fully modulating so you don't have to adjust the heating load you can however have the boiler start on less gas for heating (i.e have the gas valve open for say 75% rather than the 100% it comes set for out of the factory)but that is different from adjusting the heating load and most installers wouldn't even know how to go about this.

Tipper · 9 Dec 2008

Madmog said:
I would say you are doing fairly well to be using only five units a day if your system is running 24 hours. Would anyone agree? We have our heating on approx four hours a day and use approx 4 units which I think equates to about 40kw.

Which just goes to show that keeping your heating on 24 hours/day is more economical that just a few hours once or twice a day when the boiler spends all it's time getting the house up to temperature rather than just keeping it there.

spoony77 · 9 Dec 2008

Tipper";p="1077442 said:
Madmog said:

Which just goes to show that keeping your heating on 24 hours/day is more economical that just a few hours once or twice a day when the boiler spends all it's time getting the house up to temperature rather than just keeping it there.

Click to expand...

Is this true?

The wife keeps telling me this but i just laugh at her is she right!?

big-all · 9 Dec 2008

no because
the heat loss at night is reduced as the room temp reduces

if you leave it on normal temp at night you have greatest heat loss all the time

if a boiler can bring the house up to temperature in one hour why would it be cheaper to have a boiler modulating all night!!!!

bmxboy · 9 Dec 2008

big-all";p="1077480 said:
if you leave it on normal temp at night you have greatest heat loss all the time quote]

You wouldn't leave it at 20 degrees at night as it would be too hot to sleep, the ideal night time temp is 16-17 therefore the amount of time the boiler fires up at night is reduced significantly.

D_Hailsham · 9 Dec 2008

bmxboy said:
The boiler guy suggested a smaller boiler but since the new boilers are self modulating they shouldn't have any bearing on gas usage.

tonybhoy said:
Boiler is fully modulating so you don't have to adjust the heating load

See //www.diynot.com/forums/viewtopic.php?t=158935 for a discussion on the need to range-rate an oversized modulating boiler. The OP had a 38kW boiler with an overheating problem, which disappeared when the boiler was turned down to provide the required 24kW max output.

D_Hailsham · 9 Dec 2008

turbofan said:
sounds like your property is heating up quicker and looseing heat even quicker through cavity walls.
so the new higher output boiler is working hard to maintain an even temperature and burning for a longer time period.

There is no scientific basis for saying that.

The rate of heat loss is determined by the difference in temperature between inside and outside. It has nothing to do with the rate the house is heated.

For a house to get warmer, the heat being produced by the radiators must be greater than the heat being lost through the walls, i.e the heating input must be greater than the heat output. Once the house is up to the desired temperature, all the radiators have to do is to produce enough heat to balance the loss through the walls.

The greater the heat input, relative to the heat output, the quicker the house will reach the desired temperature, which is why radiators are frequently oversized by 10-20%. This is OK if you have a working family and the house needs to be heated up for an hour in the morning and again at 5 or 6pm for the evening. But if a house is occupied all the day - retired people for example - then the over sizing may not be so important.

Tipper · 9 Dec 2008

big-all said:
no because
the heat loss at night is reduced as the room temp reduces

if you leave it on normal temp at night you have greatest heat loss all the time

if a boiler can bring the house up to temperature in one hour why would it be cheaper to have a boiler modulating all night!!!!

But you miss one essential thing.....the fabric of the building won't get up to temperature in one hour but if left on, and yes a slightly lower temperature is more comfortable, the building reaches a steadier state and thus the heat loss through the walls will be offset by not having to warm up the structure again and again.

big-all · 9 Dec 2008

Tipper said:
But you miss one essential thing.....the fabric of the building won't get up to temperature in one hour but if left on, and yes a slightly lower temperature is more comfortable, the building reaches a steadier state and thus the heat loss through the walls will be offset by not having to warm up the structure again and again.

the temperature off the building fabric cools much much slower and has a lot lot less influence on heating rate compared to other factors
this obviously ecludes the outside walls

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New boiler has resulted in increased Gas usage

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