Published on February 14th, 2023

A Guide to Central Heating and Heat Pumps

As a core component of your home, central heating should be high on the list of areas to review while considering retrofit. After many years of minimal change within this space, the needle has begun to move with a renewed focus on heat pumps.

12 mins Retrofit Guides How to be more energy efficient Handy Guides Heat Pumps

As a core component of your home, central heating should be high on the list of areas to review while considering retrofit. After many years of minimal change within this space, the needle has begun to move with the renewed focus on heat pumps, thanks in part to the UK Government’s grant schemes for consumers.

What you might not be aware of is the close relationship between heat pumps and underfloor heating.

Both systems function comparatively slowly and have a low flow temperature - that is, they operate more efficiently when they provide a temperature only a few degrees higher than the ambient internal temperature. Compared to the frenetic burning of gas from a boiler, which tends to provide heat at the 60 to 70 degree range, UFH provides heat in the mid 20s. Due to its increased coverage and lack of cold spots, it can heat a larger space at a lower temperature.

Book a home assessment and start your journey to a healthier home with Furbnow.

Contents:

  1. What is central heating?
  2. What are the different types of central heating?
  3. How does central heating work?
  4. How do you control central heating?
  5. What's the most efficient way to run central heating?
  6. What are heat pumps?
  7. How do heat pumps work?
  8. How efficient are heat pumps?
  9. What types of heat pump are there?
  10. What is an air-source heat pump?
  11. How does an air source heat pump work?
  12. What is a ground source heat pump?
  13. How does a ground source heat pump work?
  14. Can you retrofit a heat pump?
  15. What should I consider when getting a heat pump?
  16. What are the main benefits of heat pumps?
  17. How much does it cost to convert to a heat pump?
  18. What are the ongoing costs for a heat pump?

Read on for our complete guide to heat pumps and central heating:

1. What is central heating?

It is a system in your home that means you can heat your house. In most houses in the UK it comprises a central ‘furnace’ (usually a boiler) which heats up water before pumping it into pipes, which lead to radiators, or to the taps, providing hot water.

Once used, the water goes back to the boiler for reheating and pumping out the next time it’s needed.

In a standard boiler / radiator set-up, there are two potential boiler setups. A conventional boiler, which consists of a pump, a timer and a room thermostat. You control the heating and hot water separately, by using the timer. The hot water needs to be heated in advance of use.

The other option is a combi-boiler. In this setup the boiler controls the heating, and heats hot water on command - so you don’t have to worry about setting timers, or running out of hot water. 

Read: 7 signs your home isn’t energy efficient

2. What are the different types of central heating?

There are a number of types.

  1. Wet central heating
  2. Warm Air Systems
  3. Underfloor Heating
  4. Electric Storage Heating

Wet central heating is the most used in the UK and is the boiler + radiator combo you most likely know. Pipes transfer hot water through the house providing the heating.

Warm Air Systems bring in air from the outside, before heating it in a boiler and then distributing that via vents in each room. They are useful in smaller houses without rooms for radiators.

Underfloor heating (UFH) can either be wet (via pipes) or dry (via electric cables) and works by heating the floor, rather than a radiator. Heating tends to be more even with UFH than with radiators as it covers the whole floor and there aren’t any ‘cold spots’.

Electric Storage Heating is also known as ‘night time heating’, is a form of radiator that is designed to specifically utilise off-peak electricity tariff prices. It warms ceramic or clay bricks inside it overnight, and then releases the heat from them during the day.

Read: From heat-pumps to insulation: 5 ways I can reduce my bills for good

3. How does central heating work?

The heat that exists to help you warm your house is stored in natural gas as a chemical compound. Your house is connected to a main pipe which brings natural gas into your home. 

When the heating turns on, the boiler burns the gas, transferring this heat energy from the gas to the water.

Once the water is hot, an electric pump pushes the heated water through the system. Most modern heating systems use a two pipe layout to manage this. 

One pipe carries the hot water around the house, and into the radiators, and a second pipe takes the cold water back to the boiler for reheating.

The water flows through the pipes - entering radiators on one side and leaving on the other. This is a result of the water being cooler once it passes through the radiator. 

The cool water returns to the boiler and is reheated. The process repeats until the  temperature hits the correct level.

The overall heat of the system is managed by a thermostat, which turns the boiler off when it reaches the appropriate temperature.

Any wasted gas leaves via the boiler flue and is dispersed in the air.

Read: What could a whole house retrofit do for you

4. How do you control central heating?

In the majority of the systems, you control the level of heating required via a thermostat. The thermostat sits in a central location and uses sensors to detect the temperature of the room, sending a signal to the boiler to make changes if required. 

In some systems, there are also thermostatic radiator valves (TRVs). You can use TRVs to add an extra layer of control to each radiator, by setting the level of heat required per room. They use the heat from the radiator to know when the correct temperature has been reached, at which point  the valve from the pipe to the radiator is shut to prevent hot water continuing to heat the radiator above the required temperature

You also have the option of a Smart Thermostat or Smart TRVS - these are linked to an internet connected hub which allows you to control your heating remotely, either for the whole house or by setting a specific temperature for each TRV.

Finally, with conventional boilers, you can programme a timer for when you want the heating to come on and go off. You have less control with this, but it’s useful for a routine and making sure you have enough hot water available.

Read: How to improve the energy performance certificate of your home and reduce your bills

5. What’s the most efficient way to run central heating?

Is it more efficient to turn on the heating when you’re cold, or have it running consistently over the course of the day to keep the ambient temperature up?

From a cost and energy perspective, it is more efficient to only use the heating when you need it. This is because you’re likely to burn less fuel if you do this.

You should also review which rooms you spend most time in and adjust your TRVs to be warmer in these rooms, and colder in the others. This will ensure there is minimal wasted heat.

If you have a timer, you should also set the heating to come on 30 minutes before you wake up - so the house is warm enough to encourage you out from the duvet - and off 30 minutes before you go to bed. This will ensure there is no wasted energy once you’re in bed.

You should also consider maintaining a consistent temperature at the thermostat. A typical house is warm enough between 18 and 21 degrees.

Read: How Retrofit Underfloor Heating Works

6. What are Heat Pumps?

Heat Pumps are an alternative to boilers, and an environmentally friendly way to heat (or cool) your home. In the same way boilers convert the heat potential from gas into hot water, heat pumps convert existing heat into heated air in your home. They are more environmentally friendly than boilers as they don’t require fuel to burn to create heat.

There are two types of heat pumps, air-source, and ground-source (also known as geothermal pumps).

Air-source heat pumps work by transferring heat from the air outside the home, into heat inside the home.

Ground-source pumps work in much the same way, transferring heat from the ground into heat in the home.

Heat pumps are able to both heat and cool air, so can also be used as alternatives to air-conditioning systems.

7. How do Heat Pumps Work?

Heat Pumps transfer energy from one place to another, rather than burning fuel to generate energy. Electricity is used to power the process, but the energy used is much less than it creates, and in the process used by boiler heating.

To fully grasp how heat pumps function, you need an understanding that we are surrounded by thermal energy in the air - heat. Heat naturally flows to colder environments, where there is less pressure. 

Air is a gas. When the pressure of a gas increases, the temperature increases. When the pressure decreases, the temperature decreases.

A heat pump adapts the natural process by swapping the ‘cold’ air inside our house for the warm air outside.

The Heat Pump utilises a gas known as a ‘refrigerant’. As the pump pulls the outside air in, it uses electricity to compress the gas, raising the pressure and therefore, the temperature. It then disperses this warmth as air inside the house, or into water

8. How efficient are Heat Pumps?

Standard boilers cannot operate at 100% efficiency as they can’t fully utilise all of the energy produced via the heat transference process from fossil fuel to heat. There is always some wasted gas.

In contrast, Heat Pumps can offer at least 100% efficiency during their process as they literally transfer heat from one place to another, instead of converting from one form to another. Indeed many heat pumps offer over 100% efficiency as they output more heat than they take in.

The level of efficiency depends upon the results being asked of the pump. For example, if you live in a cold climate and ask the pump to increase the internal temperature by a large amount, its efficiency will be reduced as it will need to use more electricity to reach the desired levels. In a climate where the indoor temperature is required to only be a few degrees higher than outside, the heat pump will be able to operate much more effectively. 

A Heat Pump can work and find heat to transfer in conditions up to -14C.

9. What types of heat pumps are there?

There are two main types: Air Source and Ground Source. They both perform the same basic function of getting heat from outside the house and transferring it inside, but the source of the heat is different.  

10. What is an Air-Source Heat Pump?

An air-source pump uses the air outside the house as the source for collecting heat, and as the ‘sink’ to replace the heat indoors if they’re being used to cool the internal climate.

They come in two forms - Air to Air Heat Pumps and Air to Water heat-pumps. In the UK, you’re likely to find more Air to Water heat pumps as our existing heating systems are water based.

11. How does an Air-Source Heat Pump work?

Heat from the outside air is absorbed into a fluid. This fluid then passes through a heat exchanger into the heat pump which raises the temperature before transferring that heat to water, which flows through the pipes in your home.

Air to Air heat disperses it using a Warm Air heating system via vents. This can also be used to put cold air into the house, so if you’re replacing an air conditioning unit this would be the option to go for)

Air to Water heat pumps transfer the heat into water. This water is then passed through the house, providing heat to the radiators, and hot water to the hot water cylinder.

12. What is a Ground Source Heat Pump?

A ground-source pump is a heat pump that takes the heat from the ground, rather than the air. It’s also known as a geo-thermal pump. It requires more initial installation than and Air-Source pump as it requires pipes to be buried underground before being connected to the heat pump outside your house.

13. How does a Ground Source Heat pump work?

A ground-source pump takes heat from the ground and uses it to heat both the internal space, and the water within the home.

A network of pipes are buried underground next to your home. These pipes are then pumped full of water and antifreeze, creating a mixture called Thermal Transfer Fluid (TTF). The TTF moves around the pipes, absorbing the naturally occurring heat that is stored in the ground.

When it reaches the pump, this mixture is then compressed (similar to the air source pump) and then pushed through the heat exchanger which removes the heat and transfers it to the heat pump, where it is then pushed into the home heating system.

14. Can you retrofit a Heat Pump?

Yes, in fact heat pumps are an ideal option to be part of your energy retrofit renovation. They pair particularly efficiently with underfloor heating, also a good option when you’re reviewing your heating strategy.

15. What should I consider when getting a Heat Pump?

There are several items to consider when looking at getting a heat pump.

The space available

Heat Pumps can either be monobloc or split. Monobloc systems are one block that sits outside your house, with pipes leading in. Split systems have half indoors and half outdoors. 

Monobloc systems tend to be cheaper as they’re simpler to install. Split are slightly more effective, as the heat transfer takes place indoors, so less heat is lost.

You will also need somewhere for the hot water cylinder for your hot water - unless you opt for a hybrid approach and use a combi boiler for the water.

If you have land outside, it is worth thinking about ground-source pumps as well as air-source.

The internal space heating

In addition, you should think about how you want to heat rooms. Will you be keeping any radiators, or converting to underfloor heating. Perhaps you want to install something new - such as a warm air system, and vents?

Heat Pumps work especially well with Underfloor Heating, so if installing one is part of a bigger retrofit project, this should definitely be part of your considerations

Your insulation and EPC rating

The insulation of your house must also be taken into account. The UK Green Building Council - responsible for advising on increasing the proposes that a ‘fabric-first’ approach should be taken when retrofitting an existing property. If the fabric of the house can’t retain heat (i.e. the insulation), any additional changes made to improve energy efficiency will be rendered nearly pointless as the heat will escape through gaps in the windows, walls or loft. 

Your insulation will feed into your ‘Coefficient of performance’ (COP) - which is a rating given to your Heat Pump system to illustrate how effective it will be once installed. The COP is affected by the environment and how much electricity will be required transferring the heat energy from one place to another.

On average, an air source heat pump usually has a COP rating of 2, and a ground-source heat pump has a COP rating of 3 - but it can go as high as 5. The number refers to the units of energy produced per unit used. So a rating of 3 shows that 3 units of energy are produced for every 1 used.

Getting a qualified contractor

You should ensure that your installer has been certified as part of the microgeneration Certificate Scheme (MCS). This will mean the quote and recommendation given will be tailored to your home, demonstrating costs and potential savings. 

All of the engineers we work with are MCS certified. 

16. What are the main benefits of Heat Pumps?

Energy Efficiency.

Heat pumps are much more energy efficient than standard gas boilers as they transfer heat from one place to another, rather than burn an energy source to convert it. 

Environmental impact

As no fossil fuels are burnt in their operation, there is a large reduction in carbon emissions. You will be helping reduce your carbon impact. When used in conjunction with other energy creating sources such as solar panels, it is possible to make your house carbon neutral.

Cost

Although the initial outlay is expensive, if you’re replacing an old boiler, you will start to see monthly savings.

Safety

You can replace your boiler with a heat pump, and your cooker with an induction or electric cooker and remove the need to have gas enter your house entirely.

House Value

As we move towards a net zero future, all new build properties are being constructed with an aim of zero carbon impact. As Heat Pumps don’t burn fossil fuels, they are considered an excellent part of the zero or low-carbon house of the future. By adding one to your property, you will be future-proofing it and adding value to it in the process.

17. How much does it cost to convert to a heat pump?

It will depend on the type of pump you choose, but the initial capital required is somewhere between £7k and £20k.

An Air to Air source pump is the cheapest - usually costing around £1,500. This is because it only does the heating, and not the hot water.

This is followed by the Air to Water Pump, which falls between £8,000 and £15,000. This will fully replace your boiler.

Finally, a Ground Source heat pump can cost anywhere from £15,000 to £45,000. 

All of the costs will vary depending upon the exact requirements of the installation - the size of the pump, where it will be installed and so on.

You will need to ensure your house is fully insulated to make the most of the heat pump, so do factor that in. You may want to consider upgrading your existing pipework and converting to underfloor heating.

Thanks to the government’s Boiler Upgrade Scheme it is cheaper than ever to get a heat pump - you could save up to £5,000 on the installation of an Air Source Pump, or £6,000 off a ground-source pump.

18. What are the ongoing costs for a heat pump?

Maintenance costs will be roughly £140 to £250 per year.

Running costs are slightly unpredictable as they rely purely on the cost of electricity, but to help you figure it out, you need to look at the system efficiency and multiply it by your household needs. 

For example, if your system efficiency rating is 3, and you use 12,000kWh of energy a year, you will require 4000kWh of energy for the pump. Based on a cost of 15p per kWh, you would spend £600 per year.

Your central heating system is a core component in ensuring your house is comfortable. If you’re contemplating making some changes to improve your energy efficiency, or even just thinking about moving to underfloor heating, swapping your boiler for a heat pump could be a sensible choice.

A retrofit project can be quite overwhelming. We can help you with everything retrofit - whether it’s replacing the heating system or doing a whole lot more, including insulation, underfloor heating or installing solar panels.

If you’re interested in exploring how best to replace your existing heating system with a Heat Pump, contact our customer service team here.

Book a home assessment and start your journey to a healthier home with Furbnow.

Written by

Oisin Teevan

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