On 05/03/2021 08:48, Tim Lamb wrote:


One point. I am not clear if the OP is using underfloor or radiators but
underfloor has a couple of limitations which may impact on boiler choice.

The system has a maximum running temperature in the 40-50 deg. C range.
Excellent for operating a modern boiler in condensing mode but you still
need 65-70 for HW.

Underfloor manifolds may have temperature management to deal with this
but consideration might be given to choosing a boiler with dual
capabilities.

It is UFH on both floors.
Only rads are heated towel rails in bathrooms (fed off DHR which is
mains pressure)

House is well insulated.

My Thermal store has Max temp of 60C though stat is low down, and
given the horizontal baffle .... top temp for DHW draw off is much higher.
Heating loop comes off low down so cannot exceed 60C (and likely a lot
less.

I gave a wrong figure in my OP .... I said Heating company stated boiler
requirement was output of 28kW ..... just checked it was only 16kW ...
in any event I have a current 30kW Baxi installed.

The boiler is fully modulating so combined with store it is working in
condensing mode. Run at about 60% of Max temp setting.