If you’re heading down the house renovation or extension route, it’s likely that heating is one of the jobs to tackle on your list. It was certainly the case for heating expert, David Hilton, who had an air source heat pump installed when he extended his home in 2018.
Although the property had been previously heated by an oil-fired boiler, home extension plans meant the heating had to be relocated, forcing him to make the decision to switch to a new system.
But, as with any technology, things can often change at a rapid pace, so we asked David now he’s used the system since it was installed, what are the changes he’s made and what does he think he’ll change in the future? Here’s what he said.
Why I made the switch to a heat pump
There are many reasons for buying a house and for us it came down to size. Our family was increasing in numbers, and we were also conscious that we needed to be in a good, and convenient, school catchment area. But, because budget was limited, the house we eventually bought needed lots of work.
And, when budget is limited there needs to be a priority list, which doesn’t always cover everything you have on your wish list. In our case, a new heating system was one of those items.
As the property already had central heating – retrofitted by a previous owner with an oil combi boiler as there is no gas in the street – we made the decision to keep the oil-fired central heating system and spend money elsewhere on the home. In fact, we kept it for longer than we had originally planned.
However, a growing family meant we needed to build an extension, and along with this, we made the decision to finally retire the oil boiler and install an air source heat pump instead.
The main reason for choosing an air source heat pump was down to location issues. The oil boiler was installed with the flue exhausting to where the new living room would be, meaning the oil tank would no longer be accessible for filling. I’ll be completely honest and say I also really wanted a new garden shed where the oil tank was located!
Energy prices were less of a deciding factor, as in 2018, oil was relatively cheap. But, given we had solar photovoltaic panels on the roof, I was quietly optimistic that I could manage the heat pump and solar PV operation, so that it used as much of the electricity generated by the solar panels as possible
Living with an air source heat pump
Fast forward seven years and life with an air source heat pump has been a journey of mixed outcomes, not least of all the fact it took at least a year to get used to the way a heat pump works.
An oil boiler effectively blasts heat into a home using a high temperature for a short period of time model. A heat pump is almost the opposite of that, producing a lower amount of heat delivered over a very long period of time, which is what makes it so efficient.
The other difference is that a boiler delivers the same temperature consistently to the home, whereas a heat pump will modulate its flow temperature according to the outside air temperature. The colder it is outside, the warmer the radiators will be inside.
During the first year of living with the heat pump we monitored what went well, what didn’t go quite as well and also when we were too cold and too hot. We in fact got too hot a lot!
The main reason for the temperature being incorrect comes down to how well you can evaluate the heat loss of a building, as it’s this heat loss that determines what the flow temperature of a heat pump is set to.
The current heat loss calculations are reasonably good at determining the transmitted heat loss, this is the heat that physically transfers through the fabric of the building, but the ventilation heat loss is a whole different challenge.
It’s not realistically feasible to test the airtightness of every existing home, and the calculations inevitably overestimate the heat loss of a building This in turn can lead to oversized heat pump equipment and incorrect commissioning settings, all of which then lead to inefficient operation of the heating system.
When our heat pump system was installed, the flow temperature was set quite high at around 48˚C – the level that had been determined by the heat loss calculation and the currently installed radiator sizes.
At this temperature, we were were told we only needed to change one radiator. But, we should ideally have been advised to change a further three radiators as this would have lowered the design flow temperature to only 43˚C. This which would have meant we didn’t get too hot, and the heat pump would have run more efficiently.
Changes I’ve made to date
In the time we’ve had a heat pump in the house, we have always had heat pump optimisation in mind when redecorating and remodelling. So, when re-decorating, I decided to change the extra radiators myself, and also increased the pipe size delivering heat to two other radiators. The results? The system now runs at a more comfortable, and efficient 38˚C.
The key phrase for heat pump systems is: low, slow and all about flow. So, if you can lower the flow temperature, slow the heat requirement of the property and increase the flow of water through the radiators, then the system will be optimised.
Big radiators, underfloor heating, and larger pipes are ideal, and increased home insulation is the low hanging fruit when it comes to reducing heat loss, so we have made sure our home is as well insulated as it can be, and still continually try to eliminate draughts and air leakage.
However, when reducing air leakage, we also discovered that a good ventilation regime was crucial. Why? Because as humidity changes so does our perception of heat. With higher humidity we often need higher room temperatures to feel warm. Lower humidity equals lower room temperatures and therefore more efficient heating.
So, as part of our renovations we decided to install a mechanical ventilation heat recovery (MVHR) system to ensure air quality and low humidity – even though the house isn’t a new, airtight building.
And finally, we also try and run the heating to take advantage of solar power generation and off-peak electric tariffs.
Future heat pump plans
Things have moved on in the heat pump industry since I first installed a heat pump, and the new refrigerants have much lower global warming potential. Not only are they better for the environment, but they can also reach higher flow temperatures, which means that you can heat your hot water to a higher temperature.
It also means that if you cannot feasibly change your radiators or central heating pipework, then a high temperature heat pump could still be an option, even if it is at a slight efficiency loss.
Some heat pumps are also now being specifically designed to be part of a home energy system, whereby the energy requirement of the whole home is managed as a single, harmonised system, rather than a building with bolted on infrastructure.
This is the way homes need to be managed and whenI have to change our heat pump, or in fact any of the home energy systems in the future, I will certainly want them to be fully managed and remotely monitored and optimised.
The benefits of operating in this way? As the family needs change and our requirements and lifestyles also change, so will the management of the home system, automatically adjusting settings to optimise the comfort of the occupants and the efficiency of the home system.
Currently considering making the switch? Find out the pros and cons of a gas boiler vs heat pump, and if you’re looking at installing a heat pump in a period property, make sure you follow the advice of the experts who answer the question, ‘are heat pumps suitable for old homes?‘
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