Replacement Boiler Duty Question

[Grayfly]

I have searched but couldn't find a similar recent question.

I have lived in my present house for about 30 years and have replaced the existing floor standing heat only gas boiler a couple of times. Each time it was a 23kW output, 29kW input boiler. The existing one is nearing the end of its life and I need a new one. I can't re use the existing boiler location as it doesn't satisfy current regulations. I have now found a wall mount location for a new heat only condensing boiler, flue through wall to outside space all in line with regs.

I have had two quotes so far to replace and install, however, the quotes tell me I only need a 19kW heat only boiler as new condensing boilers are more efficient. I thought a boiler being more efficient would impact the heat input not the output. In order for a 19kW boiler to produce 23kW output it would need to be more than 100% efficient. Or am I missing something?

 

[doitmyself]

I have searched but couldn't find a similar recent question.

I have lived in my present house for about 30 years and have replaced the existing floor standing heat only gas boiler a couple of times. Each time it was a 23kW output, 29kW input boiler. The existing one is nearing the end of its life and I need a new one. I can't re use the existing boiler location as it doesn't satisfy current regulations. I have now found a wall mount location for a new heat only condensing boiler, flue through wall to outside space all in line with regs.

I have had two quotes so far to replace and install, however, the quotes tell me I only need a 19kW heat only boiler as new condensing boilers are more efficient. I thought a boiler being more efficient would impact the heat input not the output. In order for a 19kW boiler to produce 23kW output it would need to be more than 100% efficient. Or am I missing something?

How do you know that the 23kW boilers were the correct size? Hopefully the two quoters carried ou a heat-loss calculation, which is why you have been quoted for a 19kW boiler. Ask them!

 

[Grayfly]

How do you know that the 23kW boilers were the correct size? Hopefully the two quoters carried ou a heat-loss calculation, which is why you have been quoted for a 19kW boiler. Ask them!

None of them carried out any calculations, they just looked at the existing boiler. I don't know if the existing boiler is the correct size, I only know that the existing boiler got us through some very cold winters when turned up to max. it's a 4 bed detached house.

 

[gmartine]

How large and how well insulated would you say your house was?

 

[Grayfly]

How large and how well insulated would you say your house was?

It is about 150 sq m. floor area and 1970's insulation standards. DHW cylinder also heated from the system.

 

[gmartine]

If you haven't improved the insulation standards over the years you may legitimately have some concern.

Get another quote and ask them to confirm the size of boiler and show their heat loss calc. Try it yourself with a couple of online heat loss calculators it's not particularly difficult.

 

[doitmyself]

The Myson Heat Loss Manager is good.

 

[Grayfly]

Thanks for all the suggestions.