Heat pumps
Our knowledge base
Here you can find more information about heat pumps: how they work, what they could mean for your home, things that you would need to consider, and what effect it might have on your energy consumption and environmental impact.
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Introduction to heat pumps
What are heat pumps, and how do they work?
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Good to know
Things you need to know before installing a heat pump.
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Who are Thermly?
A little bit more about us - and why we’re here.
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What is a heat pump?
Simply put, a heat pump is a technology that is used to heat your home, instead of a conventional boiler. They are powered by electricity.

One fundamental difference to a standard boiler is that they operate most efficiently at lower temperatures. Because of this, they are operate better in insulated properties. There are a myriad of different type¬s, operating temperatures and configurations, but the functioning principles are the same.
How do they work?
They work by upgrading the energy that already exists in the air, water or ground for use in your home. They require a bit of space externally to locate the system, and also store heat for hot water use internally, so an airing cupboard or somewhere like that is ideal. They’ve been around for decades, it’s just here in the UK we’ve been a bit slow to adopt them.

Installed properly they can be 300%-500% efficient, depending on the technology. Sounds bonkers but it’s true. It’s a combination of compression and expansion of refrigerants with very low boiling points.

Imagine the energy in the air being sucked in, concentrated in a small space so that space gets much warmer, and then it’s released into your home at a nice temperature. Well, it’s not quite that. But we’ve yet to find a simpler way of explaining it!
Is it for me?
Good question, and that’s what we’re here to establish, so please take a couple of minutes to work through our very simple set of questions by following the ‘Get Started’ button.

If your home is heat pump ready, we’ll tell you. If it isn’t, we’ll say so and tell you why, and possibly what you would need to do to make heat pumps a success in your home.
Still have a question?
We’re in the early stages of building this area, so if there’s something you haven’t found please just drop us an email using the contact details below. We’ll get back to you with a direct answer, and we’ll add it in here too if need be. If you’re the first to ask and we add your query here, we’ll send you a Thermly t-shirt as a thank you.
Frequently Asked Questions
  • Heat pumps
  • Installation
  • Support
  • Good to know
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Are heat pumps noisy?
The do make a noise, but the legal maximum is 42dB measured from your neighbour’s property. They might be a bit noisier close up. Whispering can be about 30dB and chatting is about 60dB. That should give you a good idea.
Do I need a very well-insulated house to have a heat pump installed?
Heat pumps operate ideally at lower temperatures – when they can be more efficient because they don’t work so hard. If your home is well insulated, and doesn’t lose heat easily, then it’s easier to maintain internal temperatures. This enables your heat pump to be smaller. It’s not impossible to whack a massive heat pump into something akin to a two storey tent, but we wouldn’t recommend it! The smaller the heat pump, the lower the installation cost, and the lower the ongoing running cost.
What if I have (uninsulated) solid walls?
As a minimum we would tend to recommend walls and loft are properly insulated before installing a heat pump. However, it may be the case that the costs of externally insulating a solid wall are prohibitive, in which case you’d need a bigger pump - and have to put up with the higher running costs. Our installers will talk the options through with you if you’re keen to progress.
Heat pumps aren’t massively attractive, are they?
Beauty is in the eye of the beholder, and some people do like a big white box (we appreciate that’s probably not many). However there is a growing range of heat pumps and manufacturers are finally cottoning onto the visuals, with many more smarter looking external units coming onto the market.
Is there a grant available to help with the cost?
Yes. Households can currently get a grant of £7,500 towards the cost (ch-ching!). The installer will apply for this for you if you decide to go ahead.
How long does a heat pump take to install?
You should allow a few days, depending on whether you’re having radiators and pipework replaced.
Do heat pumps provide a pay back?
It depends on your circumstances (is the politician’s answer whilst sitting on the fence). It’s a requirement of the Microgeneration Certification Scheme that accredited installers don’t promise any particular cost saving. What does it depend on? Well, how long have you got? How much you paid. How well it’s installed. The efficiency and quality of the system itself. How you use it. How you used your previous system. What your previous system was and the fuel it used. How energy efficient your property is. And so on. We’d like to say – “yeah, it’ll save you £X grand per year” - but we can’t. If you’re doing this now it’s because you see the long term value in futureproofing your home, because it reduces your environmental impact and because fossil fuels are so passe. If the government gets their heads round the problem, and decouples electricity pricing from gas pricing, you’re much more likely to be quids in too. But we’re not the government, so we can’t promise that either.
Can any plumber or heating installer put in a heat pump?
Well they could try, but you won’t get the government grant and there’s no guarantee it will work. We only engage local, fully Microgeneration Certification Scheme certified installers. We vet every installer on the Thermly platform and they need to demonstrate proven competency on the specific heat pump products they propose to install (i.e. manufacturer accreditation). We don’t let just anyone on the platform, just as you wouldn’t let anyone into your home.
Are they expensive to maintain?
They should be no more expensive to maintain than a standard heating boiler – and as with standard boilers they should be serviced regularly.
What's the difference between air and ground source heat pumps?
An air source heat pump converts outside air into heat, whereas a ground source heat pump absorbs heat from the ground. The latter needs a pipe dug into the ground – either horizontally using coiled pipework in trenches, or vertically using pipework in a borehole, whereas the former needs a heat pump fitted outside the house. Watch our video to understand more about how an air source heat pump is installed https://youtu.be/u1TyPArQtWY
How do I finance a heat pump installation?
The Government wants to encourage homeowners to install a heat pump. Since April 2022 it has been offering a range of grants for an air source or ground source heat pump, and even better, these grants went up on 23rd October 2023. The current scheme is running until 2025.
You can get one grant per property – and it’s currently worth £7,500. These grants help with the upfront cost of installing a low carbon heating system and encourage us all to make our homes more environmentally friendly.
In addition to the grant support, your local authority may offer additional low cost finance solutions, and over time we’ll be able to recommend and refer you to potential providers. If there are local council solutions in your area, we’ll sign post you to them when you go through the Thermly platform.