Gas boilers and heat pumps – is it all just hot air?

By Florence Collier CEng Meng MIMechE, humblebee

19th October 2021

Well, times are certainly interesting, albeit not in a good way. Systems are breaking, whether intentionally, or with foresight, or not, and the most tangible result – in this country at least – is a gas price spike, as well as claiming its first victims among the smaller energy providers[1].

The latest IPCC and UK CCC reports have been blunt: it’s time to stop investing in new fossil fuels, and it’s time to phase out gas boilers, ideally by 2033 and no new connections by 2025[2].

One of the fronts we need to be working hard at is our buildings which represent at least 27% of UK carbon emissions, and in particular our existing homes, accounting for 14% of UK carbon emissions[3]. In parallel we have a fuel poverty crisis: some households face a heart-breaking decision each winter to “heat or eat”.

The good news is that we have solutions that will address both those crises, and make us more comfortable and healthy in our own homes at the same time.

We are so used to gas boilers: they’ve become such a commodity and so cheap to install. We have a system and we’re happy with it. We want heat, it’s almost instant: burn fuel, heat water and there you have it. Sometimes it breaks down, so we call out an emergency gas engineer, they come, they fix. Bills are just another one of our outgoings, along with all our subscriptions, right?

Running costs aside, even if we heat our spaces to a reasonable temperature, are we also overcoming uncomfortable draughts? Are we ventilating (letting cold air in) enough to prevent

mould from appearing in the corners of the rooms and on window frames? Through our winter Thermal Imaging surveys at Transition Wilmslow there is scarce evidence of achieving both comfort and healthy environments.

So what’s the solution? Is it hydrogen to every home? At the moment the bulk of that hydrogen comes from reformed methane steam (RMS) or cracked methane[4], and not necessarily from a renewable or waste source (like the one that recently won one of the Earthshot prizes). Both the traditional processes leak gases with higher global warming potential than CO2, including methane itself.

The inefficiencies of hydrogen supply have led leading professionals to conclude that it’s best used in grid energy production[5], followed by industrial processes (where high temperatures and steam production are needed, and where hazards are routinely assessed and can be dealt with).

We need to come off fossil fuels and fast; and we need to stop emitting CO2, so rapidly phasing out boilers is the right course of action, as there is no “green burning methane”.

Electricity based heating is our only real alternative, wherever possible, while understanding that at the moment the grid is not yet decarbonized (typically 55% of our power is currently generated by fossil fuels including coal). In order for the grid to become decarbonized, however - and with growing pressure on the electricity network - we need to both generate renewables where feasible AND reduce demand. Only by doing these two things together will a green energy future and economy be possible. And it’s highly achievable, if we put our collective minds to it…

You have the power to do your bit.

Heat pumps

Heat pump technology has hugely improved over the last decade but has had a bad press, usually due to poor design, installation, or a lack of sound commissioning.

A heat pump is not new technology (you have one powering your fridge) but is more sophisticated than a boiler: it takes advantage of the refrigeration cycle - the transition from liquid to gas and back again while taking heat out of the (even cold) air outside - and exploits those processes to give out more heat energy than the electrical energy needed to operate it. The efficiency of a heat pump is called Coefficient of Performance (COP): a COP of 2 means that 1kW electricity gives you 2kW of heat energy.

It’s important to get the size of the machine matched to the amount of heat lost from the home as its overall efficiency very much depends on it. Another key aspect is to operate it at low temperature inside the house to get the most out of it – this requires careful attention to the heat emitters in the home (larger radiators or underfloor heating) and the hot water system.

So, can I just switch my boiler out for a heat pump then? Not quite. If you did a straight swap out for your boiler you would probably need larger radiators, and you would definitely need a hot water cylinder if you haven’t got one already. And not if you want to keep your bills in check.

The most you’ll get out of a heat pump that’s been installed to just “do the job” is an average COP of about 2.5-3. This means your consumed energy (at the meter) for heating and hot water will more than halve, but because electricity cost is about 3 or 4 times gas, your utility bill will likely go up (and will rise in line with gas prices, seeing as gas typically contributes 40% of grid generation[6]).

Whole House Retrofit

But were you to invest in the fabric of your home (insulation, windows, airtightness, ventilation) while considering a heat pump, you could aim to reduce your energy demand to over 1/3rd of existing, and that, at least, would be cost-neutral in running terms. (There are also heat pump friendly, smart tariffs which you could shop around for, like this one from Green Energy UK.)

You will also save upfront cost if you manage to get the size of the heat pump down: at a cost of about £800-£1,000 / kW, you could be spending approximately £12.5k-£14k, for a 3 bed, semi detached house.

There are measures to suit all budgets – from initial interventions such as loft and wall insulation to incrementally deeper retrofits. Should you go further, say, to Passivhaus levels (EnerPHit), you would be able to run a very small unit and save significantly on running costs. You might even go as far as simply using direct electricity (electric panel radiators) and top up your hot water demand through your own solar (thermal / PV) installation.

Here’s the best part of an energy efficient retrofit: more comfort, more of the time, without even switching your heating on, and with controlled ventilation your air quality will improve, leading to a healthier environment. You can do this and “phase out” your boiler with confidence.

But, if you’re all ready to make the switch, be sure to do the research and get sound independent advice because not every home will be suited to a heat pump straight away. Manchester’s Carbon Co-op have put on a series of webinars which you can access for free.

Grant funding (England)

Following the demise of the government’s national Green Homes Grant scheme, some of that money has gone directly to Local Authorities to administer to people on low incomes and benefits: do check out their own grant schemes which are open for application until March 2022 (here for Cheshire East).

The Renewable Heat Incentive (RHI) – a grant for heat pump and solar thermal installations that is paid in instalments over 7 years – is also available for accredited, installed systems and new applications until March 2022.

The government have just announced a £5k upfront grant for heat pumps will be available from April 2022 – but it’s not a huge pot so you’d have to be quick off the mark!

Wilmslow’s Festival of Nature

Florence will be talking on 3rd November about her and her collaborators’ entry in the Home of 2030 competition, where they were one of six finalists. Book here for the event.

If you would like a Thermal Imaging survey through Transition Wilmslow, please drop us a line at

[1] [2] [3] [4] [5] [6]

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