30kW System Boiler Choice

no... because the minimum default call for heat is one minute on...many condensing boiler won't get out of minimum power in that time....you can adjust the minimum call for heat but who does that...

I only learnt this from Mr Hailsham!

much better just to use on open therm controller that demands a flow temperature and let the boiler for it self out..

Oh sorry OT isn't available in the UK!
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For example the latest Baxi boilers can modulate down to 3.5kW and Remeha are soon to launch a boiler with a 7:1 modulation ratio.

Higher turndown ratios come at a higher cost , flame stability being the achilles heel at low loads , the commercial sector has it pretty much in hand with regard to higher turndown ratios , the domestic market seem to struggle due to the costs involved due to machining/design of the premix burner , I don't know of any domestic boiler with turndown ratios exceeding 5:1 (20%) , not sure about the 7:1 Baxi , most turndown ratios are around 3:1 :confused:

With regard to the 3.5kw then that will be dependant on max input rating (12kw at 3:1) so a moot point. :confused:
lower modulation is a nice idea but with compensation controls it would have to be a very mild day to get the the heat load right down...

its all a bit of a nonsense to use low modulation to keep radiators at say 70c... thats only needed a few days a year when its -2c outside..
After reading this thread it seems google has been overloaded :LOL: , I'm with namsag not Alec on this one , seems some on here have no experience in the real world when it comes to design principles of a heating system. :mrgreen:

My house got lovely and warm when we had the dreaded 10c outside temp. :LOL:
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GW what are you so uncomfortable about with respect to what others say?

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