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RHH Calculators and Tools: Development, Feedback and Discussion

Air Source Heat Pumps (ASHPs)

Last Post by Batpred 2 days ago

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4606

Topic starter 11/05/2026 10:23 am [#2990]

We're building a series of interactive tools and calculators for the site starting with a heat pump installation sense checker that's just gone into beta. Link below.

The idea is to give homeowners enough grounding to ask the right questions of their installer (on sizing, controls and commissioning) without turning them into engineers.

This thread is the place to discuss all of it. If you've used a tool and something doesn't look right, flag it here. If you think a threshold is too aggressive or too lenient, make the case. If you have ideas for tools we should build next, bring them.

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4606

Topic starter 11/05/2026 10:26 am

We've published a flow rate and pipe sizing calculator on the site. Your heat pump is rated at a specific output, but it can only hit that output if the primary pipework can actually move enough water to carry the heat. Get the primary pipe run wrong and the system is throttled before it's even switched on.

The calculator tells you the flow rate your system needs, checks whether your pipe diameter can deliver it, and shows you velocity and pressure drop across the run. Common copper and PEX sizes are preloaded.

https://renewableheatinghub.co.uk/is-poor-flow-throttling-your-heat-pump/

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4606

Topic starter 11/05/2026 10:31 am

This tool currently runs two independent checks on a heat loss estimate (W/m² against property age and fabric, and a cross-reference against historical gas consumption) then asks four installer qualification questions covering controls, buffers and commissioning. The idea is to give homeowners enough grounding to push back on a quote before they sign anything.

It's in beta. The sizing logic is solid but the building categories and W/m² thresholds are still being refined. If you run it against a real installation (yours, a recent one you've been involved with or a horror story from the forum) and something doesn't look right, please say so here.

https://renewableheatinghub.co.uk/does-your-installers-heat-loss-figure-actually-stack-up

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Judith

(@judith)

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Joined: 2 years ago

Posts: 525

11/05/2026 4:52 pm

@editor in the spirit of helping out here. I ran the checks on our house, and it points to some inaccuracies in your sums(!) There’s two screenshots here, one our actual needed power, 8kW and one of the example quotes we had, 10kW. But the 8 should have showed as ok yet both show as a problem when the answer should be 6-9kW. Good luck finding it!.

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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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4606

Topic starter 11/05/2026 5:02 pm

@judith very helpful, thank you. I know the ranges are out and we're working on getting them accurate.

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Batpred

(@batpred)

Prominent Member Member

Joined: 1 year ago

Posts: 877

12/05/2026 10:03 pm

A great idea, very useful tool. 🙂

Another example. In this one the wording does not seem perfect.

"Sizing sense check

Heat loss of 5.1 kW = 38 W/m2 (expected 45-65 W/m2 for a 20-50 year upgraded property). Gas-implied range: 4.2-6.3 kW. The two checks disagree - investigate before proceeding. Gas consumption is a sanity check, not a precise calculation."

Essentially the house is upgraded but probably should be categorised as 20 year old.

But the gas measure is unrelated as far as I can tell.

This post was modified 3 days ago by Batpred

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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Judith

(@judith)

Prominent Member Member

Joined: 2 years ago

Posts: 525

13/05/2026 1:08 pm

Perhaps it was me but the annual gas consumption does not seem to to be used.

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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Batpred

(@batpred)

Prominent Member Member

Joined: 1 year ago

Posts: 877

13/05/2026 3:40 pm

@judith it may well be not be used in the logic of the applet, but given it is referred to in the wording, it can mislead. If that is the case, easily fixed by placing that comment on a final sentence.

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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