Factors affecting combi boiler kW-rating choice

[bengasman]

, someone I know upgraded a 24 kW to 32 kW and founf that the incoming gas supply to the house was NOT capable of supplying the 6 m² that the meter is rated for. The pressure started dropping off at little more than 24 kW.[/q]
rule of thumb: 1m3 per hour feeds 10 kw. Standard meter should be able to deliver 6m3.

 

[BlueLightning]

I agree with gas4u. Why don't you consider the Worcester Bosch 30Si.

This has a 30kW to HW and a 24kW to CH (circa 82k Btu's). It'll cost less than the 30CDi by a good margin and is better suited to your heating output than either the 30CDi or 37CDi

 

[mikej2005]

I agree with gas4u. Why don't you consider the Worcester Bosch 30Si.

This has a 30kW to HW and a 24kW to CH (circa 82k Btu's). It'll cost less than the 30CDi by a good margin and is better suited to your heating output than either the 30CDi or 37CDi

Thanks for your thoughts. I've been working out which radiators to buy and I've realised that I'd missed off the lounge from my original estimate (doh !)

This takes my max radiator output to about 20kW.

Now the 30Si is rated at 7.2-24kW for CH and the 30CDi is rated at 8-30kW (37CDi is 9.8-30kW)

Would your recommendation still be the same with my revised total ?

I'm guessing that you need to allow a certain amount of overhead when sizing a boiler - or to put it more simply - the boiler must always be more powerful than the total radiator output ? This would also allow for upgrading or adding extra radiators in the future.

One last question - assuming that both the gas and water supplies are sufficient, should the 37kW model (15.1lt/min) give a more powerful shower than the 31kW model (12.6lt/min) ?

It seems kind of obvious to me that it should, but I thought I better check I wasn't missing something !

Cheers.

 

[Dan Robinson]

Whilst I am sure this is all sound advice, when sizing a combi you look to your hot water requirements.

If a 24kW combi will not do for your heating, it sure as hell won't do the hot water requirements.

 

[afc017]

If you do not want a long dead leg (cold water before it turns hot) a preheat may be a good option..the preheat just heats water and stores inside the boiler for when a demand is called. it reduces dead legs considerably. I couldnt tell you which boiler was best but from my experience green stars are very badly made. I fit one just a few months ago that leaked from poor design. case of boiler falls apart aswell.. 42kw will not make any difference to weather operating two taps at once reduces pressure. unless you have a a larger diameter pipe say 22mm for you mains and HW which is unlikely you will have the flow problem.

 

[Happyplumber]

mate u wanna stop replying to posts made in 2007!!!