How much KW of gas does your combi use per hour?

matelodave

A rough ad ready guess would be if your old boiler is 80 %efficient and a new one is 90% then you could potentially save about 10-12%.

Dunno what  your gas bill is but even if it was £1000 a year you'd save the princely sum of £100-£120.

A shiny new boiler could cost £2000 installed which means it would only take you 16-20 years to get your money back

BUFF

It's not just the efficiency of the boiler itself but also the CH controls used*, building construction & local environment, what temp you heat to & if you have a DHW tank how well matched it's size is for demand/how well insulated it is & what temp. you keep it at.

As Astria says it will probably cost you more to change a working boiler than it will save. When it needs major investment/repairs though it may be worth biting the bullet (will also improve your house EPC if selling) ...

*when I replaced my balanced flue, non-condensing Worcester Highflow with a fan-flued condensing Highflow (properly set up to condense most of the time) I reckon that over 13 years the energy savings have paid for the installation - however, I reckon that 1/2 of that was due to upgrading the controls from basic programmer+TRVs to a more advanced programmer+room stat+TRVs. There is probably another few % efficiency to squeeze out by replacing with a load/weather compensating stat but that won't pay for the cost of standalone replacement (will do with next boiler replacement).

molerat

richardjones9191 said:

RelievedSheff said:

We have a 3 year old detached house running a 30kW Ideal Combi boiler with 10 radiators. 

I am currently working from home and for the last couple of days have had the heating on all day as it has been a bit chilly. Yesterday we used 42kWh of gas, today looks set to be a similar amount. 

When it isn't quite so cold outside and I don't have the heating on all day a more normal figure for our house is around 30kWh of gas at this time of year.

Hi thanks for you reply, That seems very good! I have just checked my smart meter and so far it has used 19kwh of gas today and heating has only been on for 1 hour 30 mins. Seems my boiler is highly inefficient perhaps.

If that is heating the house from cold then it will use more in that first period than it will once the house is warmed up and maintaining.  I have a good old 1985 boiler, highly inefficient, heating my 3 bed detached with 11 rads + background in my conservatory in N Scotland and the most I have ever used with the heating on for 24 hours a day is 12 cu m which is around 134 kWh so <6 kWh per hour on average.

wild666

What you use per hour will be dependant on what you use in heating and hot water. My Combi boiler uses around 1 unit, between 11.2 and 11.4 kWh, of gas per hour, kWh dependant on calorific value, last week I used 9 kWh of gas, less than one unit on the smart meter.

JohnSwift10

I use approx 67 kWh of gas a day for a 3 bed semi with the heating on all day from 07:45 to 23:30 with about 20 - 30 kW of gas used in the first 2 hours, to raise the temperature up to 21 deg C from whatever it has dropped to during the night when the heating was off and a couple of showers.

Then the heating kicks in every so often during the 13 3/4 hours  left in the day, about 2 - 3 kW every hour until 23:30.

colmel16

We changed our boiler in April this year and have been happy with the results. Old boiler was a gloworm 26 yrs old running a similar system to you ie tank fed and hot water storage for a 3 bed semi. Not full year results yet but 2021 for June, July, Aug, Sept we averaged 80 kWh for each month compared to 290 kWh for the same months in 2019 and 2020. For December we averaged 47.5 kWh per day and our only gas appliance is the boiler. New boiler is Ideal logic.

meinnit

Astria said:

Don't worry about the difference between a normal boiler and a combi boiler, worry about the efficiency of your boiler.

Check the SEDBUK rating of your boiler to easily compare.

Mine is stated as 'A' as is 88.6% efficient.

The Potterton Suprima that you mention has a rating of 78%.

The most I've seen is 91%.

All these figures depend on everything being ideal of course, so all figures could be lower in reality.

Before you start ripping out a good working boiler, consider how much you could save compared to how much it costs to replace.

You'll only get the top of end of efficiency if your system is set up to optimise condensing eg. Correctly sized radiators, low return flow etc. If you put it on max you won't hit anywhere near the quoted efficiency rating

Combi boilers are useful for low usage households as you don't need to keep a tank full of water warm all day only to be used a few times

savers_united

Usage is obviously dependent on outside temps, but what I have found is that I can use 100kw of gas in 24 hours and 85kw in 7 hours. For older / larger properties there is mileage in having the heating on longer periods using the room stat to control the temp, if I just blast it for a few hours here and there I can use just as much as leaving it on all day. 

markin

The 2-3K may be better spent on solar, and manually heat the water or spend the £350 on a solar diverter

Coffeekup

JohnSwift10 said:

I use approx 67 kWh of gas a day for a 3 bed semi with the heating on all day from 07:45 to 23:30 with about 20 - 30 kW of gas used in the first 2 hours, to raise the temperature up to 21 deg C from whatever it has dropped to during the night when the heating was off and a couple of showers.

Then the heating kicks in every so often during the 13 3/4 hours  left in the day, about 2 - 3 kW every hour until 23:30.

Your house must be nicely insulated, in your case it'll be cheaper to never have the heating turned off