New heat pump heating system underperforming in Italy... Advice needed!

Air Source Heat Pumps (ASHPs)

Last Post by robinlawrie 3 months ago

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robinlawrie

(@robinlawrie)

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Topic starter 19/08/2025 11:09 am

hi all, first post! I've just renovated a house in southern italy and spent a fortune on a 20kw heat pump system with two inverter fancoils, ducted to all rooms, for heating and cooling. the house is large and not well insulated hence the large capacity of the system.

the heat pumps (there are two, in master/slave config) are 10kw Ferroli Omnia 3.2. they are connected to a 150 litre buffer tank (i think thats the correct term) which then feeds the two fancoils which are situated above a false cieling in the main corridor.

here is a link to the brochure of the heatpumps, for reference:

having lived here for one winter, and most of a summer, i have been observing the system. firstly, in winter it struggles to get the house over 18 degrees, and in summer (when its 37+ degrees outside) it struggles to cool it under 26 degrees.

the installer has said repeatedly that it needs to be left on 24h a day to achieve the desired performance. this may well be true, however i have noticed a strange behaviour which is likely also contributing:

the control panel of the heatpumps reports the heat/cooling output of the two machines, and ive never seen the combined total go over 12kw in either heating or cooling mode.

usually it reports around 3-4kw for one machine and 5-6kw for the other.

the other day i checked it specifically after running for half an hour in cooling mode, with the water temperature set to 7 degrees (quite low for decent efficiency, but im trying to get the house cool, and i have solar panels so free electricity during the day)

water output temp reported from the pumps was 12 degrees and the return temperature was 16 degrees, this means to me that the buffer tank was not yet cooled down, hopefully eliminating the fancoils from the equation.

main pump was outputting 5.2 kw, slave was 6.4 kw. this is about as high as ive ever seen it.

what could be the cause?

the installer is being slippery, saying "its normal the output will vary all the time" "you are lucky, imagine the bills if it was running full tilt" and "leave it running all day itll be fine"

Once we have a decent battery system, ill be more happy to leave it running when theres no sun, but currently, leaving it on 24 hrs a day would absolutely massacre us on the bills, and thats without it running at the rated 20kw.

besides, thats a different discussion.

This topic was modified 3 months ago 2 times by Mars

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