Estimate your home's Heat Transfer Coefficient (HTC) — the key number that determines the right heat pump size. Cross-check your MCS installer's quote before you sign.
Methodology based on the work of Michael de Podesta — physicist and heat pump pioneer.
📊 Based on real physics🎯 MCS sanity check tool🤖 AI-powered analysis🆓 Completely free
🌡️ Household Temperature Profile
Enter the temperatures you keep different zones of your home at during winter. This lets us calculate your average daily indoor temperature — a key input for the heat loss calculation. Think about morning, daytime and sleeping temperatures.
Lounge, kitchen — when occupied
Hallways, spare rooms, daytime bedrooms
Bedrooms overnight
Typically 6–8 hrs (evenings + morning)
Typically daytime if out at work
Overnight sleeping hours
Calculated average daily temperature:
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🚿 Hot Water Usage
We need to separate the gas used for hot water from gas used for space heating. This is important because a heat pump handles both but at different efficiencies — and getting the split right gives a more accurate HTC.
Each person uses roughly 50 litres of hot water per day
This affects hot water consumption significantly
Estimated daily hot water energy:
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⛽ Gas Consumption & Boiler
Your annual gas consumption is the foundation of the calculation. Look at last year's gas bill for the total kWh figure — or use your smart meter data. This is the single most important number you'll enter.
5,000 = small flat · 15,000 = average house · 30,000+ = large house
Check your boiler's installation date if unsure
The coldest temperature your heat pump must handle. -3°C suits most of England; -7°C for Scotland.
🏠 Your Home Details
A few details about your home help us calculate the insulation figure of merit and give context to your heat loss result — and help our AI give you more specific advice.
Total heated floor area across all floors
Enter this if you have a quote to cross-check
Sometimes shown on MCS design documents
All data stays in your browser — nothing is sent to any server except the anonymised values used to generate your AI analysis via Claude.
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Heat Transfer Coefficient
W/°C
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Suggested Heat Pump Size
kW
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Insulation Figure of Merit
kWh/m²/year
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📊 Calculation Breakdown
⛽ Annual gas consumption
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🚿 Hot water energy (estimated)
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🔥 Space heating energy (thermal)
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📍 Location heating degree days
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🌡️ Average indoor temperature
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🏠 Reference temperature (HDD basis)
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📐 Floor area
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🔍 MCS Quote Sanity Check
Compare our estimate against your MCS installer's figures. A well-sized heat pump should be within 20–30% of this estimate. Large discrepancies warrant a conversation with your installer.
Our estimate — Heat Pump Size
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Based on your gas usage & location
MCS installer's figure
Not entered
From your MCS design document
Enter your MCS figures in the Home Details step to see a comparison.
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AI Analysis & Recommendations
Powered by Claude — personalised to your specific home profile
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