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How to Zone with a Single Room with UFH

Air Source Heat Pumps (ASHPs)

Last Post by Judith 1 year ago

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Renewables345

(@renewables345)

Eminent Member Member

Joined: 1 year ago

Posts: 14

Topic starter 19/09/2025 1:27 pm [#2469]

Hi all,

I am currently looking at a project to fit an ASHP for a client. I haven't come across this before, but I wouldn't imagine it being too uncommon nowadays. The ground floor is all radiators except for one room, which is an extension with underfloor heating. The first floor is then radiators. What are the options here?

I tried speaking to Vaillant, but I didn't seem to get anywhere, what's your guys recommendations.

Thanks,

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Judith

(@judith)

Prominent Member Member

Joined: 3 years ago

Posts: 555

21/09/2025 12:45 pm

We have exactly what you describe, one utility room with UFH but radiators elsewhere.

Design one single open loop, increase radiator size if need on a room by room basis. Use a down-mixer for UFH section from overall design flow temperature (often 45C or 50C) for worst external temp (often -2C).

The installer was trained through the Heatgeek system, changed the main pipe flow from ashp to DHW cylinder from 22mm to 26mm diameter and also about 15m of first section of main feed to radiators. The only “thermostat” box is the Vaillant control box in the entrance hall. Weather compensation set up with the slope parameter at 0.6.

The key to getting the design right is the heat loss analysis of the house. Personally I like the Heatpunk software.

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