Retrofitting an Air Source Heat Pump
1 year on from installing an ASHP to a 1970s property
Since moving into our house 7 years ago (a detached, 4-bedroom 1970s build) one downer was the oil boiler that sat behind the kitchen and powered our heating and hot water.
The boiler smelled bad, it was noisy, required a huge tank of water in the loft, and was attached to a 1,000 litre oil tank in the garden that also smelled bad.
Over the years I looked into gas as an alternative, but the cost of installing a mains pipe as well as replacing the internal systems seemed prohibitive. It also didn’t seem like the best long term option given environmental concerns.
Eventually I heard of air source heat pumps as an environmentally friendly way of heating a home. However there was a lot of FUD around the technology at the time, and the upfront costs seemed prohibitive.
Eventually though we got three quotes to try and find a solution:
- In 2019, with the Renewable Heat Incentive (RHI) in mind we got a quote from a company who did a survey in-person, took a lot of measurements, but they never followed-up after the home visit. They didn’t seem very credible so we dropped it.
- A quote from EDF in mid-2020, who had a good financing model — small up-front payment, then sign over the RHI payments (which are phased over 7 years) to them to cover the majority of the cost. However this was for a hybrid heating system — so you still keep the oil boiler in place, and add to that equipment with a heat pump to take load off (EDF claim up to 80%). I was determined to get rid of oil completely and make our system less complicated, not more, so this wasn’t something we continued with.
- The government’s announcement of the doomed Green Homes Grant in late 2020 prompted our third quote from a local company who seemed very knowledgeable and credible. They came back with a reasonable quote as well as a realistic assessment of the challenges of retrofitting a new heating system to a 1970s house.
Once we decided to go ahead, the details of pressing ahead required a few further visits, and we established a few issues we would face:
- We needed a bigger and more modern immersion tank than the one we had in our airing cupboard
- We were hoping to put a replacement immersion tank in the loft, but the pitch of our roof was too steep to fit any of the available models
- We discussed putting the immersion tank in the garage at the front of the house, but it was too far away from the rest of the house’s plumbing to be practical
- Our power shower needed replacing, as the new system would go from gravity fed (from the smelly water tank in the loft) to an unvented system where water pressure would be even throughout the house
The placement of the immersion tank was the biggest issue, and we eventually settled on sacrificing one bedroom’s built-in wardrobe and building into the bathroom a little.
The other issue was the Green Homes Grant application process, which was badly administered at all levels, but we were lucky to have been successful in applying and receiving the grant in a reasonable timeframe.
Once designed, the installation itself took about 4 weeks, as there was quite a lot of work that needed to be done, including:
- A large amount of pipework, a lot of it fixing decades of bad plumbing over the years
- Taking out the old immersion tank, which appeared to have had the airing cupboard built around it
- New electrics and monitoring equipment for the heat pump
- Removal of the old boiler
- Small extension of the old oil boiler’s concrete base, to fit the new ASHP
- Replacing the power shower
One thing we didn’t do was to replace a single radiator in our house.
This has been a source of FUD around ASHPs for a long time. We have relatively modern radiators downstairs, and very old single-panel radiators upstairs. All of them are under-powered compared to what our heat loss survey recommended, but we didn’t have the budget to replace any at the time of installation.
How has it been?
We’ve been very happy with the heat pump — yes it takes longer to heat the house, but with smart controls it’s not been a problem for us. We just set the timer to heat a few hours before we’re up in the mornings.
There were a few times where the house was a bit cold for a few hours, as it takes about 3 hours for the house to heat up once you’ve changed the thermostat. But given the house is at a constant, moderate temperature, it’s not been a major issue.
One of the concerns people have before installation is about the noise from heat pumps — this is not something I’ve had any issues with at all. In fact when we’re in our garden, our neighbour’s oil boiler burns louder than our ASHP.
Other benefits I hadn’t considered was the consistent water pressure we now have across the house is great, I was very happy to get rid of our noisy power shower. I also took great pleasure in cutting up the water tank in the loft and boarding over where it used to sit collecting dust, dead spiders and other gross gunk.
Installation Cost
In total the system cost us around £12,700 to install, £600 for extra plumbing (ie new shower), and £300 for oil tank removal. So with the GHG payment about £8,500 in upfront costs. We also qualified for around £2,500 in RHI payments, phased quarterly over 7 years, so eventually that will be more like £6,000.
Running costs
It’s hard to compare running costs with oil year-on-year, as both oil and electricity prices have gone haywire since we had the system installed.
If our electricity had stayed at the rate of 16p/kWh it was when we had the system installed, our 12 month costs would have been £646. As it is, the energy prices pushed that up to £992.
As the chart below shows — we started feeling the effects of energy price rises in November 2021. As we’re with Ecotricity they do not qualify for the energy price cap.
Would the running costs have been cheaper with oil? It’s hard to tell as I didn’t track the figures accurately beforehand.
My best guess is we got through about 1,400 litres of kerosine each year. If the oil price stayed £0.43 p/l as it was on the day our heat pump kicked in, that would have come in at £632, so including delivery costs and the electricity cost of running the oil boiler, probably slightly more expensive than the ASHP.
Of course oil prices have been anything but stable. Assuming a standard year’s order pattern, the oil cost would have been more like £1,200.
Carbon emissions
More importantly though, the main reason we took the decision to install a heat pump was to reduce our CO2 footprint. So how does that work out?
Assuming 1,400 litres of kerosine oil burned per year, according to carbon-calculator.org.uk that amounts to 4,152 kgCO2e. Over 4 metric tonnes! Every year!
That’s pretty satisfying — and roughly equivalent to taking 2 and a half cars off the road!
Finishing up
Our installation didn’t include getting rid of our 1,000 litre tank in the garden. We ended up paying £300 for a local oil company to empty the tank and take it away.
It also didn’t include removing the old oil boiler, which was large and very, very heavy. It was in good condition so we tried selling it on eBay, but had no luck there. In the end we got a local scrap metal company to come and take it away for free.
