Search with Wattson

Notifications

Clear all

Joining the Renewable Heating Hub forums is completely free and only takes a minute. By registering you’ll be able to ask questions, join discussions, follow topics you’re interested in, bookmark useful threads and receive notifications when someone replies. Non-registered members also do not have access to our AI features. When choosing your username, please note that it cannot be changed later, so we recommend avoiding brand or product names. Before registering, please take a moment to read the Forum Rules & Terms of Use so we can keep the community helpful, respectful and informative for everyone. Thanks for joining!

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

Air Source Heat Pumps (ASHPs)

Last Post by Judith 1 hour ago

2 Posts

2 Users

0 Reactions

17 Views

RSS

ragtime27

(@ragtime27)

New Member Member

Joined: 7 hours ago

Posts: 1

Topic starter 13/06/2026 4:23 pm [#3058]

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

Heat Loss Report — 10_34 12_06_26.pdf

This topic was modified 2 hours ago by Mars

Quote

Topic Tags

heat pump design

Judith

(@judith)

Prominent Member Member

Joined: 3 years ago

Posts: 537

13/06/2026 10:10 pm

I wasn’t sure reading your quote if I had correctly understood that they predicted you would be paying more in bills than at present. Then on p36 is is in no doubt that is what they predict. You don’t comment on that which I find surprising.

They don’t say how big your existing cylinder is (which might be my oversight in a quick skim read)., therefore it’s difficult to understand why they want to move it to the loft, where it will loose more heat, being outside your heated envelope. The DHW is the big disruptive aspect.

You've got nice big primary piping so no need for replumbing there. I don’t understand your comment on cold water feed dimensions, since you need less supply capacity with a cylinder than with a combi-boiler. What have I missed?

Taking the TRVs off seems unnecessary, because the old analogue ones close down gradually and don’t impact the volume suddenly (and hence induce fast cycling). You might want to keep them especially in the bedrooms for comfort and preference.

Yes 50c is on the high end but using 45C might mean changes to radiators which mean the room is less easy to use afterwards. You’ll only know if they do you a 45C quote too. But the radiators are easily changed later

In general it’s a sensible proposal to me but I’m sure other eyes will see what I didn’t.

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

ReplyQuote