Living with a heat pump

Who should read this guide?

If you are living in a home with a heat pump for your heating system, this guide will give you some general information about what to expect from it and how to get the best out of it. It isn't specific to any particular sort of heat pump, and it isn't about how to choose them. It does explain some things you should know if you move into a new home that has them.

What does a heat pump do?

A heat pump is used to heat your home using electricity and heat energy from outside – either the air, the ground, or sometimes a pond or stream. It works like your fridge. Your fridge pumps heat from inside the fridge to the outside. It uses electricity, because normally heat would flow from warm to cold and the pump is pushing it the other way. However, you can transfer 2-5 units of heat for each 1 unit of electricity used. This makes it much more efficient than electricity used directly, as in an electric heater or an electric night storage heater.

At the moment, gas central heating is usually similar in cost and carbon emissions to heat pumps. However, as we get more and more renewables for our electricity, the heat pumps will be more low-carbon. (It is hard to know what will happen to the relative prices.)

Payments from the Renewable Heat Incentive

It is possible that your system is registered with OFGEM and you will get quarterly payments through the Renewable Heat Incentive (RHI). However new homes in development schemes are not eligible for the RHI – only retrofits or custom built homess.

The RHI payments are based on the amount of renewable heat (heat minus the electricity used) that the system has been assessed to supply. It is very unlikely that this will actually be measured. The payments last for seven years.

What it looks like

Most people have an air to water heat pump. This takes heat from the air outside and puts it into the water that circulates around your radiators. The outside part of an air source heat pump looks like the outdoor fan on an air conditioning unit. The inside part is a large box (containing pumps etc) connected to your heating pipes with some controls. This is likely to be in a cupboard or utility room.

For a ground source heat pump most of the outside part is underground.

Heat pumps are more efficient when delivering lower temperatures

The main thing to remember about a heat pump is that the higher the temperature it is asked to deliver, the less efficient it will be. If you are used to gas central heating you will expect your radiators to be hot to the touch. However, most heat pumps can’t deliver those temperatures efficiently, so you can expect your radiators to be warm but not hot. Also, many homes using heat pumps have under-floor heating that works very well at the lower temperature.

Since it is supplying low temperature heat, your heat pump will not be able to heat the house from cold quickly. In cold weather you will need to run it all the time. This would be very wasteful in an old, leaky house. However, heat pumps should only be installed in well-insulated homes that don’t lose heat quickly. It will cost you more to run the heat pump for a short time at a high temperature, than to run it all the time at a lower temperature.

You may have an auxiliary heater but this should only be used occasionally

Your system should be able to deliver all your heating needs (room heating and also water heating) almost all the time. Most heat pumps have an auxiliary or booster heater that comes on if the heat pump is not enough by iteself. However, the auxiliary heater only gives you 1 unit of heat for each unit of electricity so it is much less efficient than the heat pump. It should only come on very rarely - just a few days in the year.

The auxiliary heater is not the same as the de-icing heater. The auxiliary heater is for heating inside the house. The de-icer is just to make sure the outside heat exchanger does not ice up. This will come on automatically when needed.

How do I know it is working?

You will hear the pumps running, when the system is working. For a ground source heat pump that is all you will hear because the rest of the system is underground. For an air source heat pump you will be able to hear the fan running outside.

You can also check the temperature of the radiators. These should be warm to the touch but not hot. If you have under-floor heating then it may be hard to detect the heat with your hand. However, if you put a book on the floor for 20 minutes or so and then pick it up the side that was on the floor will feel warm.

If you are seriously worried that your under-floor heating is not working properly, an infra-red camera is the best way to check for cold spots – you may be able to get a survey inexpensively from a local charity such as Cambridge Carbon Footprint. You can also use an infra red thermometer such as this one from Maplin. Thermometers gives you a temperature reading at one spot, rather than across a whole area but they are relatively cheap – from about £20. You can use this to scan across the floor and see if there are areas that aren’t getting warm.

You should also have a way to check the temperature of your hot water tank, if you have one.

What do I need to do? Is there anything I shouldn't do?

You may need to experiment with your controls to see what is best for you. Try not to make the system generate higher temperatures than necessary because this will be less efficient and you will notice this on your electricity bills! The important setting is the temperature that is being delivered to your radiators i.e. the heating circuit. The room temperature thermostat does not affect the efficiency. The heating circuit temperature will probably be 40-55°C for radiators or 30-40°C for underfloor heating.

Keep radiators and floor heating surfaces clear

If you have under-floor heating, do not cover the floors with carpets because they will reduce the heat flow into the room. Similarly, don’t hide radiators behind furniture. Doing this will make them less efficient so you will have to increase the circulating temperature which makes the heat pump less efficient – and increases your bills.

If you have radiators you should bleed them regularly in case of air locks and make sure the radiator circuit has corrosion protection - just as you would with traditional central heating.

Adjust the room heating

For the room thermostat and timer, it is usually best to run the system all the time, perhaps with a slightly lower thermostat setting overnight (e.g. 20°C during the day, 18°C overnight). If you turn it off completely overnight it could take a long time to warm up again in cold weather. (If you have solar electricity panels and want to use them as much as possible rather than electricity from the grid then you might try turning the heating off overnight. However, if you find it takes a long time to heat in the morning so you need to increase the circulation temperature for your radiators or under-floor heating then it is probably not cost effective.)

Heat pumps should not be turning themselves on and off at frequent intervals. If it is turning itself on for periods of less than about 15 minutes try reducing the temperature for the heating circuit – for the radiators or under-floor heating. This will also make the system more efficient.

Many heat pumps have weather compensating controls which means you don’t have a single set temperature for the heating circuit – it depends on the weather. In these systems you will be able to adjust the ‘heating curve’ or the ‘comfort level’.

Your heating system is likely to have a holiday mode for when you go away. When you set this you tell it when you are coming back and it will start the system up again 1 or 2 days before so your home will be warm in good time. If you turn it off and back on again when you return it will take a long time to get your home back up to a comfortable temperature.

You can turn the heating off in the summer time just as you would for a gas system.

Adjust the hot water temperature

Assuming you have a hot water tank, it should be heated to 60°C occasionally to control bugs such as legionella. Your system may have a ‘disinfect’ mode or a ‘legionella mode’ for this. The rest of the time, you should set a lower temperature: 40°C to 55°C. What you need depends on how much hot water you use and the size of the tank. If you have a lot of baths then you will need hotter water but you can run a shower at 40°C. If you have a separate control for the temperature of the hot water heating circuit then this needs to be 5-10°C warmer than the temperature you have set for the tank.

You should heat the hot water tank just for an hour or so each day, maybe morning and evening – the same as you would with an immersion heater or a gas heating system. It should be sufficiently well lagged to keep warm the rest of the time. In any case, you will probably not be able to heat the hot water tank and supply room heating at the same time.

If you don’t have a hot water tank, then you can experiment with what you need for the hot water delivery temperature.

Check the auxiliary heater isn’t coming on frequently

Your controls should allow you to monitor how often the auxiliary heating is used, if you have one. This should only be needed very occasionally for the room heating. However, if you have set a high water tank temperature it may be used for that.

Why is it making that noise?

All heat pumps make some noise – like a refrigerator. Also you may hear some odd noises when valves open and close such as when the system switches between water heating and room heating. However, if you hear any other clanks, bangs or bubbles, then something is wrong. You will also notice the fan noise from the outside part of an air source heat pump. This should not be intrusive.

What maintenance does it need?

Your heat pump should have a regular service, just like a gas boiler. The engineer will check the circulating fluid levels, check for leaks, clean filters and heat exchangers and lubricate the pumps if necessary.

If the fan on your ASHP gets clogged up you should clear it. Also, the outside unit for an ASHP will have a drain so that when the de-icer runs the cold water can drain away. This must be kept clear.

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