“What do the rest of us do about heating?” or why an Air Source Heat Pump may not work for you.
Over the last year or two, the term “Air Source Heat Pump” (ASHP) has entered the national lexicon. It’s been in the papers, it’s been on the TV, you may even know someone who has one of these mythical beasts installed. To the casual observer, ASHPs are being presented to us as the magic answer to help the UK reach net zero by 2050. There’s even been talk about gas boilers being effectively “banned” in the next few years. I have had friends and neighbours ask me “Where can I get a heat pump from? My boiler has packed up.”. If only it were that simple.
As an owner of a 19th century solid brick property that, with the best will in the world, probably leaks heat like a sieve but with a strong desire to move away from burning fossil fuels I very soon came to realise that an ASHPs was not going to be a good fit.
So let’s talk for a minute about what an ASHP is and why it may not be the best solution for your home either…….
What does an ASHP do?
It effectively pulls ambient heat from the air and through a condensing process (not unlike a refrigerator or air con unit) it can warm the coolant contained within the system, turning it in to a gas, which then gets pressurised which makes it hotter which is then used to warm water. This water can be stored in a hot water cylinder and/or pumped through your radiators or underfloor heating to heat your home.
ASHP - the pros:
They can supply your heating and hot water.
They are efficient. Although they still require electricity to operate, much is made of their Coefficient of Performance (COP). This is the ratio between electricity input vs heat output. You will see claims of a ratio of 1 to 3 or 1 to 4 for example, meaning for every 1 kwh of electricity input you will then get 3 or 4 kwh of heat. This is very appealing.
They can make use of your existing water filled radiators/underfloor heating
They do not produce carbon when operating and when driven by a renewable supply of electricity such as a green tariff from your energy supplier they are helping us all move to net zero.
ASHP - the cons:
A typical ASHP produces warm water at a temperature of 35 degrees for heating and 55 degrees for hot water. Compare this with a typical gas boiler that produces hot water at 70 degrees. If you pump that same 35 degree water through your existing radiators then it will take a lot longer to heat the space. To mitigate this, several further steps are suggested:
replace your radiators with bigger radiators
replace your existing pipe work with wider pipes allowing a higher volume of the lower temperature water to flow
install underfloor heating
increase the insulation of your home, not just the loft but internal/external wall insulation
take steps to make your home air tight
leave the heating running 24/7 to slowly build to the desired room temperature
Unfortunately many of these mitigants will cost money and cause significant disruption to your home.
The cooler the air temperature outside the harder the ASHP has to work to produce the desired temperature. The harder it has to work, the more energy it consumes and the less efficient it becomes. This is where the claims of a COP of 1:3 or 1:4 can be misleading (and based on warm summer air temperatures) as it is in the colder months that we need heating and this is when the ASHP will be at it’s least efficient.
ASHPs require a hot water cylinder to store the hot water. For many homes, we got rid of our hot water cylinders and airing cupboards when we were convinced to switch to gas combi boilers with the promise of instant hot water. We will now need to think about sacrificing space in our home for a large hot water cylinder.
ASHPs require ongoing maintenance. They are complex devices that operate outdoors in all conditions often running 24/7. Think of them like a fridge operating in your back garden. They should not be considered maintenance free.
ASHPs are relatively large devices that need to be located outdoors. They also produce some level of noise as they have a condensor and a large fan. Although, a single ASHP may not be too audible, if you live in a compact residential area and all your neighbours have similar devices the accumulation of this noise may be significant.
ASHPs require outdoor space to be located. For those who don’t have sufficient outdoor space ( those living in flats etc) this is not an option.
So, in summary, if you live in a new build, or even better a “passive” house, where your home is air tight, well insulated and you have the space and the money to throw at an Air Source Heat Pump and the various heating system upgrades that may be needed then an ASHP might work for you.
However, if like many millions of us in the UK, you live in an older property or flat and don’t have the outside space to give up to a large fan and condensor or the indoor space to give up to a hot water cylinder, or the £18k + that it night cost for installation and upgrades, what do we do? Do we just stick with our gas boilers? Does that make us part of the “problem” rather than the solution? Are we the “baddies”?