Sizing boiler

[akist]

When selecting a gas boiler the gas people (who have been to quote) calculate how many radiators, how many watts each, and the hot water cylinder, and they come up with a required boiler wattage. They have, all, so far, settled on the Bosch 35kW boiler.

I did some counting and I have 24 radiators and 29kW. Plus 15-18kW for the HW cylinder. Plus losses on the pipes, total maybe 50kW. So the Bosch 35kW is too small?

However the heat pump men said that a typical modern 450m2 house loses 15kW of heat, does that mean I only need a 15kW boiler (excl HW) ?

Also, is there any calculation anywhere about the amount of water inside radiators and pipes to correctly size the pump (or pumps) and expansion tanks?

 

[ianmcd]

Do you own a hotel ?

 

[muggles]

You wouldn't add that much for a cylinder unless you have very high hot water demand. Generally we don't actually add anything. The correct way to size a boiler is to use a proper calculator such as www.heat-engineer.com Highly unlikely you need 35kW let alone 50kW

 

[akist]

OK, my latest calculation shows 28kW (heatadviser) without losses on pipes and without hot water cylinder. I suppose the 35kW would be OK.

One more question if I may, is it possible that flow does not reach some remote radiators because it loses pressure at the previous ones? Or is it a case of increasing pump power until the most remote radiators also see some flow? Just wondering how it works in practice.