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Heat pump design review please: 5 kW Vaillant aroTHERM Plus heat pump

ragtime27 · 2026-06-13T15:23:43Z

Hello all, I have received the heat pump design from eon after 6 weeks of waiting here's key points: The estimated heat loss is approximately 3.92 kW. with proposed a 5 kW Vaillant aroTHERM Plus heat pump. This sizing is based on continuous heating (24/7 operation) and does not include spare capacity for intermittent heating or temperature setbacks. A 250-litre Vaillant hot water cylinder is included in the proposal and is to be installed in the loft space, subject to a suitable base being constructed by a third-party joiner and approved by a structural engineer. Two radiators are proposed for replacement The proposed system flow temperature is 50°C for -1.7°C(London suburbs) scop 3.41 TRVs are proposed to be removed from all radiators to ensure sufficient water flow through the heat pump system. This helps support defrost cycles and improves overall efficiency in line with an open-loop system design. Upgrading the existing 15 mm mains cold water supply is not included within the scope of the heat pump installation. is the temperature flow 50°C quite high? Can I insist on lower design temp? primary pipes 28mm branching to 22mm then 15mm to the rads no UFH, propery is fairly insulated. is it a haggling process with eon since they can swap up to 60% of rads also, the existing water tank and the header in the loft seating just above a bearing wall. my concern is getting a structural engineer to calculate the load, only to tell me that it has to go where the existing tank is seating. what the solution here, do they need to swap and putting the cylinder, however platform is needed beforehand. have i missed anything I have attached the design proposal Many Thanks

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Air Source Heat Pumps (ASHPs)

Last Post by Judith 1 hour ago

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Judith

(@judith)

Prominent Member Member

Joined: 3 years ago

Posts: 538

15/06/2026 5:30 pm

@ragtime27 some rooms in our house only have one place where a radiator could easily go and the (possibly) larger radiator for 45C might mean putting it elsewhere. In our smallest bedroom that would mean a clash between the bed and the door. It depends on the detailed shape of your rooms.

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP >4) open system operating on WC

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