The gas boiler arrives

After the recent post on gas boilers, Alan Clarke gave the following pointers relevant to our ultra low energy refurb...


With a small  radiator system it isn't critical to have an ultra small boiler, but roughly speaking the capacity of the radiators ought to match the minimum boiler output - though this will be higher than your heat loss (smallest system boiler is 3kW min I think).

If you'll be having a combi, these have to be reasonably powered to heat water quickly enough for a shower - and hence have a higher minimum output too at 6-7kW - so will need more radiator capacity.

Then I think it is important to have good controls to control the radiator temperature, to derate the output to suit the low heat load of your house.

I like the rehema avanta boilers for dealing with low heating loads this way, these have either a simple room-compensating controller, or a fancy programmable thermostat, which also offers weather compensation. But having used one of these with a local builder in a passivhaus he's asked to use Worcester Bosch for the next job as they are easier to deal with for spares and servicing - and Worcester Bosch now also do boilers with "intelligent controls".


In the event we have gone for an Atag - but it may be some time before know whether this was a good choice or not. Hopefully we'll have moved back in and be using it for hot water in the autumn, and won't need to heat any radiators until November / December....