18/06/2026
How well does a heat pump work in an old house?
After 5 years of learning from the best I designed and installed my first Air Source Heat pump with a full heating system. After living with it in our 300 year old home for over a year and a half I’m blown away with how well it works. The cheapest and best way to heat our home.
Constantly warm in every room and a full year- whole house energy bill of £1547 for heating, hot water, cooking, washing and every thing else. No solar, no battery. That’s a family of 4 in a 5 bedroom historic house (250m2) with predominantly solid wall construction. (Note- Partial year on the OVO heat pump tariff and partial year on a standard rate tariff).
2025 full year SCOP shown as 5.6 (note that comparing Viessmann SCOP with independently monitored Viessmann performances - real world SCOP likely to 4.6-5.6). That’s at least 460% efficiency over the year for heating and hot water.
From July, a £9000 grant is available when replacing an oil boiler (or LPG boiler). £7500 for a Natural Gas boiler or direct electric heating replacement. I would almost always install a heat pump system on a full renovation like this or a new build. Retro fit can be more of a challenge but the vast majority of UK homes are suitable.
What about the installation cost? With the £7500 BUS grant I received I estimate it was £2500 cheaper than an oil heating system or £4500 cheaper if a new oil tank and trenching to be installed. I think it would be a similar cost to a new Natural Gas boiler and system of this size.
The plant room area was a luxury space to work in- most systems only need an airing cupboard inside.
The system is future proof and running costs could reduce even further if we get solar and or batteries.
Thanks to Damon Blakemore for the MCS, commission day and technical phone support when installing the kit for the first time.
OSO Hotwater (UK) Ltd Viessmann Climate Solutions ESBE Ltd
