Renewable Heating Systems

Heating systems can use renewable sources of energy, as opposed to gas, oil and coal.  Heat makes up two-thirds of the energy used in the home.  Moving to a renewable heating system such as heat pumps can make your home zero carbon if combined effectively with renewable electricity generation and storage, and a renewable electricity supply. 

As heating makes up around 25% of our carbon footprint, moving to renewable heating systems plays a massive role in tackling climate change.  When a new boiler is required, we all should be considering the following systems to replace our gas or oil heating.

Heat pumps

Heat pumps take the ambient energy from the environment close to the house and use it to heat water, which in turn is used for heating and washing.  Electricity powers the system.  Due to the ability to withdraw heat energy from the surrounding environment, these heat pumps deliver around three times as much heat energy as the electricity used (based on what is known as their COP – Coefficient of performance).

Replacing existing heating systems

Gas and oil powered heating systems can be effectively replaced by heat pumps in the majority of houses in the UK, as they can operate at -15 degrees centigrade.  Due to the UK’s Renewable Heat Incentive (RHI), these units pay for themselves within 7-8 years and have warranties of 20+ years, resulting in long-term savings for the household.

It is necessary for houses to be more energy efficient for these systems to operate effectively, as water is heated to 45-50 degrees centigrade as opposed to 60-65 degrees in gas or oil boilers.

Which heat pump to choose

Whether your property has land or water nearby will determine which system is chosen.  Air source heat pumps are the most likely renewable heating alternative in terraces, flats and houses without land.  They are also less expensive to deploy, but do not generate quite as much heat as the two other alternatives, placing increased demands on the energy efficiency of the home.  

A mixture of heat pumps may be used for very large properties.

Air source heat pumps

Air Source Heat Pumps (ASHPs) are units that sit outside of the house and vent air into a compression unit.  Water is then heated by this compressed air, from which the house receives hot water.  It operates like a domestic fridge running in reverse and can operate when the temperature is as low as -15 degrees centigrade.

Costs

Installing a typical system costs between £6,000 and £9,000, and will save around 1.8t CO2 per annum.  At least £100 a year will be saved on bills, in moving over from a gas boiler, and the saving will be higher if this replaces oil or electric heating.  With the RHI mentioned above, around £700 will be received for the installation per year, resulting in the cost of a unit being paid back for within 7-10 years.

Concerns

Common concerns about Air Source Heat Pumps include the noise associated with venting the air and the size of the units, which are approximately 100cm x 100cm x 50cm, and need to be placed outside, with good ventilation.  Most members of Better Century have had positive experiences of using these units.  Do ask them questions if you have any concerns.

Ground source heat pumps

A ground source heat pump (GSHP) uses pipes buried in the earth to extract heat from the ground. This heat can then be used to heat water.

The heat pump circulates a mixture of water and antifreeze through these buried pipes known as the ‘ground loop’.  The heat from the ground is absorbed into the fluid and then passes through a heat exchanger into the heat pump.  The ground at a depth of one metre stays at a relatively constant temperature throughout the year, so the heat pump can be used even in mid-winter.

The length of the ground loop depends on the size of your home and the amount of heat you need. Longer loops can draw more heat from the ground, but need more space to be buried in.

If space is limited, a vertical borehole can be drilled instead, where the heat is drawn from a greater depth but using less ground area, the downside being that this tends to be more costly.

Costs

Installing a typical system costs between £10,000 and £18,000, and will save around 1.8t CO2 per annum.  At least £180 a year will be saved on bills, in moving over from a gas boiler, and this saving will be higher if this replaces oil or electric heating.  With the RHI around £1,500 will be received for the installation per year, resulting in the cost of a unit being paid back within 7-10 years.

Concerns

The advantages of such a system are that they do not depend so much on the energy efficiency of the home and that they can heat large houses.  They do not have the noise concerns of air source heat pumps but do rely on major excavation of land which remains a significant concern for many.

Water source heat pumps 

Water source heat pumps work by extracting heat from a river, lake, large pond or borehole. They use submerged pipes containing a fluid similar to that used in ground source heat pumps to absorb the heat.

Water sources are often more efficient than ground and air sources, as heat transfers better in water and temperatures are also generally more stable throughout the year (between 7 and 12 degrees centigrade).

There are closed loop and open loop systems.  Closed loop heat pumps have sealed pipes filled with fluid, which never comes into contact with water directly.  Open loop systems draw water from the water source and extract the heat before discharging the water back out.  An open loop system is more effective, but requires consent from the relevant Environment Agency.

Costs

Installing a typical system costs between £9,000 and £12,000, and will save around 1.8t CO2 per annum.  At least £220 a year will be saved on bills, in moving over from a gas boiler, and savings will be higher if this replaces oil or electric heating.  With the RHI around £1,800 will be received for the installation per year, resulting in the cost of a unit being paid back within 6-8 years.

Concerns

The amount of heat that can be extracted from a water source is a concern, therefore large water reservoirs are required.  The installation is less disruptive than a ground source heat pump, but can cause concern for the disruption of aquatic life. 

Solar thermal

Solar water heating systems use panels connected to a domestic hot water system to reduce or eliminate the need for the boiler to run in sunnier weather.  In most cases, solar panels cannot be used with combi-boilers, as they require a special hot water tank with a second heat exchanger loop for the solar circuit.

There are two main types of solar water heating collector: flat plate and evacuated tubes. Evacuated tubes generally have a slightly higher output than flat plate systems, offsetting a higher purchase price.

Installing a typical system costs between £4,000 and £5,000, and will save around 260kg CO2 per annum.  Hot water savings will be around £50 a year, with the RHI contributing around £250 per year for the installation, resulting in the cost of a unit being paid back for within 14-16 years.

If a house moves to a heat pump, this type of system will not have carbon emission savings, but will still attract the RHI.

Biomass heating

These are wood-fuelled systems that burn wood pellets, chips or logs to provide heating to a house or a single room.  These systems are considered renewable as the wood burnt is replaced through new growth, which captures the same amount of carbon as is emitted.

Biomass boilers

Boilers can be used in place of a standard gas or oil boiler to heat radiators for a whole house, and to heat the hot water.  These systems rely on a consistent feedstock such as pellets or chippings, which need to be bought especially for the system. Biomass boilers work in the same way that regular fossil fuel ones do, where fuel is burnt in the boiler which produces energy that is used for heating.

There are 3 main types of biomass boilers: low temperature hot water (LTHW), high temperature hot water (HTHW) and steam.  LTHW biomass boilers tend to be the most common replacement for fossil fuel boilers.  These types of boilers require a plant room to house the boiler and fuel.

Installing a typical system costs between £14,000 and £16,000, and will save around 1.8t CO2 per year.  Around £250 a year will be saved on bills in moving over from a gas boiler, and the saving will be higher if this replaces oil or electric heating.  With the RHI around £1,300 will be received per year for the installation, resulting in the cost of a unit being paid back for within 6-8 years.

A downfall of such a system is that ash needs to be removed from the unit on a regular basis.

Biomass stoves

Stoves are very useful for heating a single room and may also be used to cook food.  They will save on heating, but this depends upon the size of the room and how often the system is used.  These systems do not attract RHI funding.

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