Will heating your house constantly use more energy?

We are advised when we get a heat pump to change the heating schedule to be constant, or nearly so. This is because heat pumps are efficient when supplying gentle heat but not good at heating a home from cold quickly. This is completely the opposite of what we have learned about keeping our bills low when using a gas boiler. So how much are we currently saving, and how is this different with a heat pump? I have investigated this with a model of a semi detached house (using similar models to my work for BEIS [1]). In the boiler case, savings from intermittent heating are substantial - up to 21%. In the heat pump case, the difference is much less - at most 4%. 

Scaling up heat pump installation – counting the benefits

It is generally recognised that reducing carbon emissions is going to mean lots of heat pumps (or other electric heating systems) installed in homes to replace gas and oil boilers. However, heat pumps are (currently) more expensive to run and to install and not many households have been persuaded so far. The government is running a public consultation now on a market mechanism to increase the install rate [1]. By their own assessment this policy has a net social cost of £0.6 billion over 4 years. So how can this be sensible? Or is there a fundamental problem with the cost benefit analysis? - I think there is.

This chart illustrates the balance in costs and benefits – it is quite finely balanced.

Data from the consultation 'A market based mechanism for low carbon heat' cost benefit analysis [4]

Are buses doomed?

Bus use has been in decline since well before Covid - in fact since deregulation in 1986 and more recently - since about 2012 - even in London. Cycling on the other hand is on the increase. Many schemes have tried to persuade people to switch from cars to buses with limited success. More home working is likely to increase commuting distances making buses less practical. More and more people are discovering the joy (and health benefits) of electric bikes. Purchase price is a barrier for some but you can now buy an E-bike on a subscription basis for less than the price of a bus season ticket. Is there still a role for buses? - probably, but less for commuting and not the same sort of buses. (This is an opinion - tell me if you agree.)

The main driver for shifting is to save time. Low cost has a lesser role.

Environmental awareness has an impact but the main driver of mode choice is to save time - even in the context of free bus fares. This diagram illustrates the mode shifts observed in the various studies described below assuming very low cost or free bus travel. Cheap fares do increase use of buses, but a lot of this is due new travel demand or shifting from walking. On-demand buses are preferred because they are quicker to use than normal buses and more accessible to people with mobility needs. On-demand buses can also be quicker than walking or cycling in some circumstances. E-scooters and E-cycle are often quicker than the bus and sometimes quicker than a car.

Squatting on the Grid?

A friend has been complaining to me about EV charging stations being unusable for months on end - Soham and Sutton EV chargers in particular were mentioned. What is the hold-up? It could be equipment problems, or perhaps delays in getting capacity on the grid to supply - or is it unscrupulous business practice? It seems complete madness to me but Euan McTurk talked about this in an interview with Robert Llewellyn on his Fully Charged Show (12th Nov, about 4 minutes in). He seems to think large companies may be grabbing up capacity on the grid for fast chargers and not bothering to commission or maintain the equipment - but while they are there no-one else can get on without paying huge sums for a grid upgrade. 

These charging points in Soham have been 'coming soon' since December 2020

Can this be true?

Review of the Heat and Buildings Strategy

Last month the government announced the long awaited Heat and Buildings Strategy [1] which sets out plans to convert this sector to net zero GHG emissions. This came out almost at the same time as the wider Net Zero strategy [2]. One aspect I was particularly interested to see was the plan for hydrogen in heating – there is still indecision in this area we will have to wait until 2026 for more certainty. Another aspect is the balance between electricity and gas energy costs, also support for retrofitting heat pumps into homes and building up the supply chain for retrofit. There are definitely some good things in this policy but some serious gaps.

Scenarios: high hydrogen, high electric or in-between? 

The future role of hydrogen is still uncertain and the Net Zero Strategy refers to three scenarios for heating in the future. In all cases, heat pumps have a very large role. As well as the net zero in 2050 target there is an interim target to reduce GHG emissions from this sector by about two thirds by 2035.

By 2035, the target is for 13 million homes to be on low carbon heating of which two million will be on heat networks. For the rest there are different scenarios. If hydrogen does not work out, almost all the rest will be on heat pumps. If hydrogen does work out, then we can expect up to 4 million on hydrogen gas by 2035 and 7 million on heat pumps. Or, it could be something in-between.

Whatever happens, at least a third of homes in the UK need to be heated by heat pumps by 2035 – a lot more than on hydrogen.

How much does it cost to install a heat pump?

The recently announced Net Zero Strategy includes a boiler upgrade scheme with a £5000 grant towards installing a heat pump. How does this compare with actual heat pump costs? To be fair, you should bear in mind that when you upgrade your boiler you only need a new boiler slotted into the same space as the old, whereas when you convert to a heat pump there are additional one-off costs for plumbing and other work. So subsequent heat pump upgrades will cost less. Still, there is no doubt that heat pumps cost more than just replacing a boiler, which is usually £2,000 to £3,000. Here are some top level estimates for a heat pump installation – as you can see they vary greatly We will break this down in a minute.

Energy Savings Trust (2021)	£7,000 - £13,000
Renewable Energy Hub (2019)	£5,000 - £8,000
EDF Energy (allows 20% for installation costs)	£5,000 to £10,000
Heat Pump Retrofit in London (Carbon Trust, 2020)	£7,000 (3.5 kW) - £11,000 (11 kW), mean £8,800
Cost of domestic heating measures (Delta EE, 2018)	£9,000 (8 kW) - £15,000 (16 kW)
Development of trajectories for residential heat decarbonisation to inform the Sixth Carbon Budget (Element Energy , 2020) – excluding the fabric upgrades.	£10,000 (mean).

Turning down the radiators in unused rooms

To reduce our heating bills we are often advised to turn down radiators in rooms that we are not using. However, this can be a bad idea if you have a heat pump. The adjacent rooms leak heat into the colder room which means the working radiators have to work harder. This is generally OK with a boiler but not with a heat pump which gives better efficiency at low temperatures. With the radiators working harder they need to run hotter which often means you end up using more energy rather than less [1]. I have done some modelling to see what this effect looks like. The savings on the overall heating demand is probably smaller than you might think – typically 3.5-5.5%. On the other hand the impact on the radiator heat demand surprisingly high – 20% or more.