Are you heat pump ready?

Whilst certain sections of the British media would have you believe you can only fit a low-temperature heat pump after gutting your house, insulating every last surface and replacing all elements of the existing heating system, this is simply not the case. These self same ‘experts’ have loudly decried heat pumps as ‘not suitable for the British climate’, despite their successful deployment in the far more frigid climes of Scandinavia for decades (and, more latterly, Ireland). Behind this blanket dismissal of anything new or progressive, hides a nugget of truth - albeit misleadingly phrased in order to promote panic amongst the good folk of Middle-England:

‘Heat pumps are not suitable for the British housing stock’.

Or, that phrase can be flipped to read ‘British housing stock is not suitable for heat pumps’, which is more accurate, but still not strictly true.
Technically, all properties are ‘heat pump ready’ - it’s just that some would require far larger units which would be much more costly to run. Some (but certainly not all) may require the existing ‘flow and return’ pipework to be upgraded if the existing setup is on thin, ‘microbore’ type pipework - i.e. anything below around 15mm diameter - although some installers have been able to work around this. Around 70% of properties will require some radiators to be upgraded so that the same level of comfort can be achieved at a lower flow temperature of 45oC, versus 65oC+ for many traditional boilers. The lower the flow temperature is, the larger the emitter needs to be to provide the same amount of heat as a higher temperature boiler would have.

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Do try this at home

A good experiment to test your home for a heat pump is to turn any radiator valves to fully open, then turn your combi boiler’s* flow temperature down from around 65oC to 55oC (go even lower if you’re brave enough!) and see how long your home takes to get to target temperature. You will probably find you need to extend your heating periods to achieve a good level of comfort, as instead of ‘blasting’ the home with heat and then letting it cool down again, running ‘long and low’ continually ‘tops up’ the heat being lost from your home through the fabric and draughts to maintain comfort. Congratulations! Not only have you made your existing boiler run more efficiently (and cheaply), you’ve also experienced how it is to live with a heat pump - running long and low, with minimal impedances around the system. Additionally, you’ll have a better idea as to what rooms struggle to reach temperature - indicating possible radiator upgrades ahead of time.

*Not suitable for ‘regular’ or ‘system’ boilers with a hot water cylinder due to the risk of Legionella. Always refer to the manufacturer's instructions if in doubt.

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Future proof heating

Heat pumps, running on electricity instead of gas, can slash your household carbon emissions by around 70% - a figure that will only increase as the grid further decarbonises with more renewably generated power. So, if your main motivation is reducing carbon emissions and you can afford it, install one as soon as possible.

Unfortunately, the electricity unit price is currently around three times that of gas - although one of the major selling points of low-temperature heat pumps is that a well designed and commissioned system should run at 300%+ efficiency. This means that for every unit of electricity a heat pump uses, it will provide at least three back in the form of heat - the theory being that your new heat source should cost you no more to run than the outgoing gas or oil boiler. In practice, some heat pump systems achieve even higher efficiencies: 400, or even 500%+ have been attained, meaning running costs can even be (considerably) lower. There is also lobbying from the electric heating industry, who want to see the fuel unit price lowered. Somewhat ironically, the current unit price is set by the cost of gas powered electricity generation. If this was to be decoupled, and reattached to a cheaper method (such as wind generation), then the unit price could be reduced.

Wow! So I could be quids in?

Yes and no! If you only currently run your heating system in a very frugal manner i.e. for a couple of hours per day, and you accept feeling cold outside of those times, then your fuel bills will inevitably rise due to the much longer heating periods required to run the heat pump well. You will, though, be heating your home to a comfortable temperature, which will have numerous benefits for both the health of the building and its occupants. You’ll also be saving almost £120 per year for the gas standing charge too (provided you don’t have other gas appliances, obviously!).

Your bills would also rise if you were to treat the heat pump like a gas boiler - short ‘blasts’ of heat would lead to it running inefficiently as it attempts to run at full tilt to rapidly heat the house - i.e. the polar opposite of how it should be running. In this case, your home will struggle to ever get to the target temperature, your bills will go up and, through no fault of its own, the heat pump will be deemed ‘not fit for purpose’. Fitting a heat pump isn’t just about changing the heating system, it’s equally about changing how you use that system too.

How much insulation do I need to install before I can fit a heat pump?

A very simple rule of thumb can be applied here - if your house is currently warm (at 18-21C) most of the time with the existing heating system, this should mean that a heat pump can be fitted, and you may just have to change some radiators and possibly some to achieve the same level of comfort at the lower flow temperature offered by the heat pump. Modern (post-1990) properties should have reasonable levels of insulation already fitted, although it’s always worth checking this due to the vagaries of building standards over the years.

If your home is currently cold, it will be no warmer just by fitting a heat pump, and, to enjoy increased comfort and reduced running costs, some retrofit works should be undertaken. There is no simple answer as to what measures you are best off employing - it is very much dependent on the individual property - but if we were to take say, a 1930s property with draught-proofing, double glazing, good loft insulation and filled cavity walls, this should be ‘heat pump ready’ for a smallish heat pump (5-6kW unit) at around 350% efficiency, depending on the quality of the installation.

The further you go with fabric upgrades, the smaller the unit you can fit. It is worth shooting for a maximum 7kW unit where possible, as this size is more likely to comply with the permitted development rules and not require planning permission, especially in more urban locations, due to running more quietly than larger units. This may be tricky due to constrictions with either the property type or budget for retrofit, but take heart, there are many ways of making a house more energy efficient, and insulating walls is not always a pre-requisite - although good airtightness and at least double glazed windows usually are. You may even find that some fairly straightforward draught-proofing work and topping up the loft insulation may be all it takes to reduce your home’s heat demand sufficiently to be able to fit a sensibly sized heat pump.

One thing to be very aware of is not substantially extending or retrofitting your home post heat pump install - heat pumps are sensitive beasts and increasing, or indeed, decreasing the heat load by too big a margin will result in the heat pump working inefficiently or struggling to meet the new demand. You do have a certain amount of ‘wiggle room’ as modern units can modulate to a degree, or you could also use a higher flow temperature temporarily, but, If possible, you want to have your home’s heat loss calculations carried out including any proposed extensions / retrofit measures you are hoping to carry out before sizing the heat pump - this way you’ll be sure to have a model installed that effectively meets both current and future loads.

Other factors to consider

Heat pumps do not provide hot water on demand - some form of water storage is required, such as a cylinder. Space can often be at a premium in the age of ‘peak stuff’, so this will have to be factored in, or possibly the cost of an alternative, more compact storage medium known as a ‘heat battery’.

Whilst the main unit is situated outside the house (at least in the case of an air source heat pump), there are still some internal parts to consider such as the buffer tank or expansion vessel, not forgetting the cylinder / heat battery too.

An air source heat pump will require some external space where it can be sited. Depending on the size of the unit to be installed, this can take some planning due to noise issues and proximity to neighbouring properties. The heat pump will need to be sited on a stable area (ground or wall) with suitable drainage to allow condensate to drain away without creating a slip hazard.

People Powered Retrofit can perform impartial heat loss calculations for your property to determine potential heat pump size and what, if any, radiators will need upgrading. We can also advise on how you can improve your home in order to fit the smallest heat pump possible, or meet a tight budget. Our ‘full’ service includes the Home Retrofit Scenarios report, which details a number of scenarios for your home covering fabric upgrade options, the impacts of installing a heat pump system at different junctures and even adding generation / storage - all with real world costs and your actual bill data included to help you make informed decisions against your current running costs.

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