Was the heatloss done based on the property’s current fabric or with the internal insulation taken into account? Another point worth mentioning is that regardless of the above, MCS calculations tend to overestimate the heat loss. 

Thanks for your reply. the heat loss was done taking into account the new internal wall insulation.

Posted by: @dannyboy

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Hi all I hope you can help. We have a 5 bed home mostly solid wall with parts of it that were built in the 1700’s. Under the eco4 scheme we have qualified for ashp and internal wall insulation. The heat loss calculation states we need a hump with an output of 16.6kw when it’s -3degrees C but they have proposed to install a Samsung system HHSM- G600016-1 which as far as I can see can’t achieve this output.  This system also seems to have been around since 2019 and therefore not as efficient as the latest system. Would there be a reason for this? I am wondering whether a cascade of a newer system comprising a 12 & 6kw system would be better?

as I say I am a noob so any info would be great

A Samsung HHSM- G600016-1 won't produce anything like 16.6kW at -3.  The link below suggests more like 12-14kW at these low temperatures.  

SECONRENEWABLES.COM "https://www.seconrenewables.com/ekmps/shops/seconsolar/resources/Other/secon-r32-price-file.pdf"

You should ask your potential supplier to explain why they are recommending an ASHP that can't deliver the calculated heat loss.  What is the flow temperature and room temperature at -3 deg ambient in your heat loss calculation? 

If your heat loss really is 16.6kW at -3 deg, by the time you factor in hot water and defrosts (the dip in the graphs in the link) you are likely to need a backup heating system or some extra jumpers.  

The newer ASHPs may be a bit more efficient but a well designed system matched to your heat loss is more important. 

 Feel free to share more details of your quote if you want further comments.

From what I have been researching that is exactly what I was thinking. They did at one point suggest cascading two pumps and the latest generation ones seem to be output stable despite external temp or that may be marketing guff. The flow temperature is supposed to be 50 degrees C and internal is 20degrees C. 

Posted by: @dannyboy

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From what I have been researching that is exactly what I was thinking. They did at one point suggest cascading two pumps and the latest generation ones seem to be output stable despite external temp or that may be marketing guff. The flow temperature is supposed to be 50 degrees C and internal is 20degrees C. 

The ones that can deliver what it says on the badge when it's cold outside will be able to deliver more under the right conditions.  A 14kW Ecodan will deliver 14kW when it's cold and can do quite a bit more - over 16kW - under very favourable conditions.  Other makes may be similar; I'm only quoting Mitsubishi because I have one.  It can all be very misleading.