Is there a benefit if range rating down

[D_Hailsham]

I have checked on various sites and the size for my property seems to come out around 10-12kW.

I have had a go at calculating the output from the site you suggested. I believe I have 1x2100w Lounge, 6x700w Bedrooms/Hall/kitchen, 4x300 small rooms of the house.

Does w means watts or wide?

I used the delta 40. Total = 7420

Delta 40 =0.748 from the Elite leaflet. So your nominal output is 720/0.748 = 9920 watts. Is that correct?

 

[Gary27]

I have checked on various sites and the size for my property seems to come out around 10-12kW.

I have had a go at calculating the output from the site you suggested. I believe I have 1x2100w Lounge, 6x700w Bedrooms/Hall/kitchen, 4x300 small rooms of the house.

Does w means watts or wide?

I used the delta 40. Total = 7420

Delta 40 =0.748 from the Elite leaflet. So your nominal output is 720/0.748 = 9920 watts. Is that correct?

Yes sorry w means watts and 9920 watts is right

 

[D_Hailsham]

So your heating requirement is 10-12kW, and you have just under 10kW of rads. But the rad output is measured with a flow of 75C and a return of 65C.

If you want the boiler to condense you need a return of 55C. In these conditions the output of the rads will be 85.4% of the nominal output; with a flow of 65C and return of 55C it will be 74.1%.

This means that your rads will not be producing enough heat to provide a room temperature of 20C when the outside temperature is below 4C (65/55) or 2C (75/55). in these conditions your only option is to raise the flow rate to 75/65 or 80/60. The number of days when the temperature is -1C or below is only about 5% of the year.

If the temperature drops below -1C you will not be able to maintain an inside temperature of 20C without supplementary heating.

I am actually surprised at these results as it suggests that the radiators in the house were considerably undersized when they were installed - presumably before all the insulation improvements were made.

I know you have used several calculators to arrive at the 10-12kW figure, but as I don't know which they are, I am unable to comment on their reliability. The Whole House Boiler Size Calculator has been produced by the Building Research Establishment and is the recommended calculator. If you use this and deduct 2kW from the result (Domestic hot water allowance) you will get a reliable answer.

 

[Gary27]

So your heating requirement is 10-12kW, and you have just under 10kW of rads. But the rad output is measured with a flow of 75C and a return of 65C.

If you want the boiler to condense you need a return of 55C. In these conditions the output of the rads will be 85.4% of the nominal output; with a flow of 65C and return of 55C it will be 74.1%.

This means that your rads will not be producing enough heat to provide a room temperature of 20C when the outside temperature is below 4C (65/55) or 2C (75/55). in these conditions your only option is to raise the flow rate to 75/65 or 80/60. The number of days when the temperature is -1C or below is only about 5% of the year.

If the temperature drops below -1C you will not be able to maintain an inside temperature of 20C without supplementary heating.

I am actually surprised at these results as it suggests that the radiators in the house were considerably undersized when they were installed - presumably before all the insulation improvements were made.

I know you have used several calculators to arrive at the 10-12kW figure, but as I don't know which they are, I am unable to comment on their reliability. The Whole House Boiler Size Calculator has Dbeen produced by the Building Research Establishment and is the recommended calculator. If you use this and deduct 2kW from the result (Domestic hot water allowance) you will get a reliable answer.

Thanks I am understanding more what you are saying, but rating the boiler right down it still reaches a flow of 55c and the house does reach 20c eventually.

I think I need to monitor the gas usage and see how much more efficient this boiler is. I do monitor usage very closely I have solar PV and am very conscious of energy usage.

Thanks for your help, my problem was that I just thought this new boiler would just work, although I do like a challage, had plenty with my PV installation.