Which boiler for existing CH system

[aroundM21]

How would I chose a Combi boiler (which I want to modernise and get rid of the loft tanks) for my EXISTING CH system ??

I have a 3 bed average semi house, the CH has 'micro' pipes, 8 Rads in all. I understand that the output from Combis is higher for DW than CH. So when they have numbers such as 18/24/28/32, what are these referring to ?? Can the CH output be 'tuned' so as not to be too high pressure for example ...

Many thanks !!

Mike - Manchester

 

[Agile]

A combi boiler is rated for the hot water output. Originally 24 kW but more recently 28 kW or even higher which gives one good shower but never full two outlets of HW.

The problem is most three bed semis need only a maximum of 10-12 kW and that is the minimum that a large combi can give on Ch so the boielr has to cycle on/off to average the heating demand which can be about 5 kW once its warmed up. Thats less efficient.

Tony

 

[gas4you]

If you have 1 bath/shower go for a Vaillant Ecotec Plus 831 and get it range rated down to around 10-12 Kw for the ch.

 

[Agile]

But 10-12 kW is the full heat required to heat a typical semi in the coldest weather when its freezing outside. The boiler then has to switch on-off which is rather inefficient.

Unfortunately the current boiler designs can only manage a modulation range of about 3:1 which makes the larger combis less efficient on heating which typically constitutes about 85% on their gas consumption.

I can misadjust a conventional burner to give about 5:1 but the premix are set in the program chip and so non adjustable.

Tony

 

[gas4you]

I agree but it's still better than a non range rateable combi running at 24Kw for ch.