This is my first post so hopefully it will attract a bit of interest.

I've just bought five 4.5kw ASHPs (Calorex AW4502) - all fairly new and taken out of a Social Housing Scheme as they were undersized for the houses to which they had been fitted - apparantly a common problem for this, the smallest Calorex ASHP.

So, I'm doing everything the wrong way round - making the buildings to which they are to be fitted suit the pumps. I'll post the issues I'm considering a couple at a time.

The first question relates to the replacement of the 134N gas with R407C. This will cost perhaps £500 per pump, parts and gas, and gives an additional 1kw of maximum output and better low-ambient temperature performance, albeit at the cost of a lower maximum output temperature. This can mean additional heating of the DHW is necessary (eg for legionella control). Can anyone comment on this factory upgrade - its performance, who can do it (in the East Midlands, UK), etc?

Secondly, for the first house, a four-bed, mid-terrace which is stripped bare just now (but it will be well insulated and have UFH fitted), I think two of these pumps will suffice in conjunction with two 5kw log-burners (one of which has a back boiler) which will be at each end of the ground floor. I'm thinking of connecting two pumps in series, though I could use one alone for DHW, and another for space (UFH) heating.

What would you do?

Andy