Sizing a boiler for heating demand

[Matt0029]

Is the usual way of sizing the boiler for a C/H system to add up the kW of all the required radiators. Then add 10% for heat loss in the pipework? I know how to do it with regards to a combi and the flow rate rate required in litres per minute with a 35 degree rise in temperature. Thanks.

 

[SJB060685]

There are several calculators online or methods in the CIBSE domestic heating guide to guide you through. Each area you calculating fabric and ventilation heat loss and ofcourse there will be some through pipework as well.

 

[Matt0029]

There are several calculators online or methods in the CIBSE domestic heating guide to guide you through. Each area you calculating fabric and ventilation heat loss and ofcourse there will be some through pipework as well.

Thank I'm fine with sizing the radiators. It's getting from that to the size of the boiler best suited.

 

[ShaunCorbs]

yep room heatloss then add them together to give you your total heat loss then 10kw for a cylinder if they want it on the same time as heating

 

[SJB060685]

As Shaun says add each room up to give you the total and add what he said for HW to it if you want CH and HW on at same time, unless you use a system with PDHW or plan to heat separately.

 

[Matt0029]

Than

yep room heatloss then add them together to give you your total heat loss then 10kw for a cylinder if they want it on the same time as heating

Thanks by room heat loss, you mean the btu or kW rating of the radiator required per room?

 

[SJB060685]

Yes the heat loss figure in KW or BTU is the required radiator size to heat each room, plus 10-20% for pipe heat loss and initial start up. Bare in mind when using some more in depth calculation methods you factor in outdoor temperature to room temperature differential, outdoor temperature often being taken as -1°c and desired room temperature around 21°c. The higher the differential the more watts required.

 

[oz-plumber]

Are you trying to size the boiler for hot water requirements or for heating only.
There could be a big difference in the hot water demand to the heat output for radiators.
All manageable with the right set up of the boiler