A Year with Our Heat Pump: One Family's Diary

When the Henderson family in Warwickshire replaced their 18-year-old gas boiler with a Vaillant aroTHERM plus 7kW air source heat pump, they kept a month-by-month diary. Every temperature reading, every electricity bill, every frustration, and every pleasant surprise. This is their year — unedited and honest — and it paints the most complete picture of what living with a heat pump is really like.

The Property

Month 1: October — Installation and Nerves

Claire writes: "Installation day was nerve-wracking. Two engineers arrived at 8am and worked until 5pm. Day two was finishing touches and commissioning. By the end of day two, the old boiler was out, the heat pump was in, and three radiators had been swapped for larger ones. It was remarkably tidy — less disruption than we expected."

Michael writes: "The commissioning took about an hour. The engineer explained the weather compensation curve, showed us the app, and set the hot water schedule. I understood about 60% of it. The radiators felt warm, not hot. Claire immediately asked, 'Is it working properly?' The engineer smiled — he clearly gets that question a lot."

October electricity cost (heating + hot water): £42

Comfort level: 7/10 — warm enough, but not confident yet

Month 2: November — The Learning Curve

Claire writes: "Week one, I kept turning the thermostat up because the radiators did not feel hot. Michael showed me the room temperature — it was 20.5°C. The house was warm. I just was not used to radiators that do not burn your hand. By week three, I stopped noticing."

Michael writes: "I became mildly obsessed with the app. Watching the COP reading in real-time, checking daily electricity consumption, comparing outdoor temperature to flow temperature. The COP averaged 3.1 this month. The engineer said that is good for November."

Sam (age 8): "The radiators aren't as hot. Mum says that's good because I won't burn myself. The house is warm though."

November electricity cost: £58

Comfort level: 8/10 — adjusting and feeling warmer about the decision

Month 3: December — The Cold Test

Claire writes: "December was the test. Temperatures dropped to -3°C on two nights. I will be honest — I was worried. But the house stayed at 20°C the whole time. The heat pump just worked harder. I checked the app: COP dropped to 2.5 on the coldest night but was still producing 2.5 units of heat for every unit of electricity. I stopped worrying."

Michael writes: "Christmas Day was the first time we had the whole family round since the heat pump. Everyone commented on how warm the house was. Nobody noticed the change from a gas boiler. That felt like the ultimate test passed."

December electricity cost: £82

Comfort level: 9/10 — the cold test, passed

Month 4: January — Confidence Building

Claire writes: "January was a turning point. We stopped thinking about the heat pump at all. It is just there, keeping the house warm, doing its thing. I compared our electricity bill to what we would have been paying for gas — and we are spending about £35 less per month. Not a fortune, but real money over a year."

Michael writes: "I switched us to a heat pump tariff this month. Lower unit rate, slightly higher standing charge. The maths works out at about £120/year cheaper than the standard tariff. Wish I had done it from day one."

January electricity cost: £88

Comfort level: 9/10 — normal life, just warmer and cheaper

Month 5: February — The Cold Snap

Claire writes: "We had a week of -5°C to -7°C in February. The heat pump ran 24/7 and the house never dropped below 19.5°C. I checked the defrost — it triggered twice a day for about 5 minutes each time. Barely noticed. Our old gas boiler used to struggle in cold snaps. This just kept going."

February electricity cost: £94

Comfort level: 10/10 — fully confident in every weather condition

Month 6: March — Spring and Savings

Michael writes: "March was interesting — outdoor temperatures started rising, the heat pump worked less hard, and COP hit 3.5. Our electricity cost dropped to £48. We have now completed a full winter. Total winter heating cost (October to March): £412. Our gas boiler would have been approximately £700 for the same period. Saving of about £290 in six months."

March electricity cost: £48

Comfort level: 10/10

Months 7-9: April to June — Coasting

Claire writes: "April: heating mostly off except for a few cool evenings. May: heating off entirely — just hot water. June: the heat pump runs for about an hour a day to heat the water cylinder. Electricity costs for heating and hot water: April £28, May £18, June £14. It is barely noticeable on the bill."

Michael writes: "We are seriously looking at solar panels now. If we can generate our own electricity in the summer months, the hot water could be essentially free from April to September. We have got quotes coming."

Months 10-12: July to September — Summer Bliss

Claire writes: "Summer with a heat pump is a non-event. It heats the water cylinder for about 45 minutes each morning and that is it. July: £12. August: £12. September: £18 as we started needing a little heating on cool evenings. Total summer cost (July-September): £42. For comparison, our old gas boiler cost about £80 in summer just for hot water."

Lily (age 11): "I showed the energy app to my friend and she thought it was cool that we can see how much electricity the heat pump uses in real time. Her parents are thinking about getting one now."

The Annual Summary

Note: Gas equivalent estimates based on the family's previous boiler consumption pattern at current gas prices. Electricity costs on heat pump tariff from January onwards.

Claire's Year-End Summary: "If I could tell myself one thing from 12 months ago, it would be: stop worrying and just do it. The first month is odd. By month three, it is normal. By month six, you cannot imagine going back. And by month twelve, you are telling everyone you know to get one."

Michael's Year-End Summary: "The numbers speak for themselves. £361 saved in year one, on a system that cost us £5,400 after the grant. That is a 15-year payback on savings alone — and the system will last 20-25 years. Add solar panels and the payback drops to under 10 years. It is a good investment."

Frequently Asked Questions

What heat pump did this family install?

A Vaillant aroTHERM plus 7kW with a 200-litre cylinder, in a well-insulated 3-bedroom semi-detached 1990s house.

How much did they save?

£361 in the first year compared to their previous gas boiler. They expect this to increase with a heat pump tariff for the full year and planned solar panels.

What was the hardest month?

October — the first month. Learning to trust the system and accept that warm (not hot) radiators still heat the house effectively.

Did the children notice?

They noticed cooler radiators (a safety benefit) but otherwise just noticed the house was always comfortable.

Would they do it again?

Without hesitation — and sooner. Their only regret was waiting.

Are they adding solar panels?

Planning to add 4kW of solar panels in year two, expecting to reduce heat pump electricity costs by 35-40%.