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....

Which gas boiler?

On the long list of decisions to make is the choice of gas boiler.

Given that hot water use will probably be higher than our heating requirements (and we are low water users to boot), we'll want a boiler that is very, very small. I'm hoping we'll be using less than 5000 kWh per year of gas in total.

A top of the price range, super-efficient boiler won't save us much, given how little gas we will use. A small and basic combi boiler at a correspondingly basic price sounds attractive right now!

Any suggestions?