My experience of installing an Air Source Heat Pump
This article comes from Mick Lorkins, CA-WN Steering Group member and founder of Northamptonshire Woodland Community Volunteers. We think it provides exactly the sort of honest and comprehensive information householders need - if you have an experience of making 'green' home improvements that you would like to share, please get in touch.
I thought I would write this article to share my knowledge and experience of installing an Air Source Heat Pump (ASHP) in my home, to give some sort of insight if you are thinking of a new heating system.
Introduction to ASHPs
There are many fears when installing a different heating system as it is a fundamental human need. Maslow came up with a ‘Hierarchy of Needs’, where food, water and heat are foundations to life. It is also a big capital investment into your house and if it does not go as planned is a worry. To reassure, it should be noted that ASHP technology is not new technology and is the same system as used in fridges/freezers and Air Conditioning units although applied slightly differently to provide heat rather than cold. In many European countries this has been the main source of heating for many years. Some air to air units (air conditioning units) can blow hot or cold air. In the UK ASHPs are generally used as an air to water system to replace an existing gas boiler.
A key element of the technology is that for every unit of energy put into the system (Kilowatts of electricity) it gives an equivalent of 3 to 4 Kw of heat out. It is therefore much more efficient than just using electric heaters or electric radiators that would only give out one to one unit of energy. This is the fundamental reason for using the ASHP technology.
The other key point about an ASHP is that it is powered by electricity and so if your electricity supply is all from renewable sources or an electricity provider such as Octopus or EoN with just renewables as an option, then you have a system with zero CO2 emissions.
Systems currently come with grants to pay for some of the capital cost. Some research might be needed to see what is on offer at the time. I installed my ASHP system just over 2 years ago when the government paid back part of the capital cost over 7 years. Now incentives from Government include a grant of £7,500 to replace a gas boiler in your home1.
How was the experience for me?
Well strangely I also have the experience of my father replacing his traditional gas boiler with hot water tank for a new gas combi boiler. The experience for both installed was surprisingly similar and the cost to me for the ASHP was half the cost of my father's gas boiler.
I had a combi boiler that was over 15 years old and was concerned about my Carbon footprint and keen to reduce this. I also wanted to plan the change at a time that suited me rather than when the old system gave up. An air source heat pump system comes with more kit than a Combi Boiler. If you don’t already know, a gas Combination Boiler (Combi) is one unit on a wall and when you turn on your tap it heats cold water from your incoming cold water supply and feeds it directly to your tap. Similarly a second feed goes on a circular loop to each of your radiators to heat your home.
A more traditional gas heating system has a hot water tank that means there is potentially a tank that sits in a cupboard to provide an airing cupboard, and a header tank in the loft to feed the system.
For the Air Source Heat Pump system there are three main items to find a location for, these being:
- An outside ASHP unit with electricity and coolant pipe to feed into the house. This unit is about the size of a double fridge, dependent on the model and make
- A sealed hot water tank about 5 ft high
- A control unit (about the size of a combi boiler)
- I also have a second smaller sealed tank to feed hot water to the radiators that means the ASHP does not need to come on and off so often but taps into this secondary reservoir of heat.
I am a project manager and in my job would always get 3 quotes before starting a project but on this occasion only got one as I saw an advert on Facebook with a company that had won awards for their ASHP installations. I would however recommend getting three quotes and research their on-line reviews for installed systems. For me it is also about how many reviews they have as well as the scoring and comments. Just 10 reviews all giving 5/5 from some mates against 2,000 views giving 4.6/5 might give a better understanding of the realistic product and service.
ASHPs run at a lower operation temperature of circ. 55oC compared to a gas boiler. The result is that radiators need to be bigger. I have talked to a few people about installing an ASHP and many try to pre-empt the system specification wanting to install larger radiators before talking to an installer. I would advise against this as any heating system would be designed for your building requirements i.e. the size of the room and the ASHP unit specified. When you buy a car you don’t go out and buy a car radiator but leave it to the engineer and an ASHP will be the same.
One point to note is that your grant might be predicated on the Energy Performance Certificate (EPC) rating and if it is already good you may not get a grant. There is a tendency to do small improvements and keep updating your certificate but it is primarily only required when selling or renting your house so you should consider the order of your house improvements, as well as grants available. It might be better to put in an ASHP, solar panels and batteries all in one go rather than a piecemeal approach, as it could cost you more if you have inadvertently improved the EPC and do not qualify for a grant.
You might also want to research ASHP to see which one you might prefer, as you would when buying a car. Some will come with different benefits such as an outside temperature gauge to more closely control your house to the outside, telling the system not to work so hard if it is warmer. You may want a certain look of the outside ASHP unit dependent on how visible it is in your garden or yard. Look at reviews and see what they say about performance.
I am pleased to say the people who designed my system got it right. The size of radiators, the thermostats on all radiators, spec for the hot water tank, and secondary radiator tank.
A few radiators were retained but generally all of them were replaced. Most of the radiators were old and inefficient so having them replaced was a good thing. At the point in the design when someone comes around to measure up I suggest you need to be there because how big and where they go is important to each room. In our hall a triple radiator was specified for behind the front door i.e. one that is three times thicker than the original radiator. I worked out measuring up the specified radiator that I would not be able to open the front door fully! I asked for it to be relocated onto the adjacent wall. At this design stage you may want to ask for changes just to give some more wriggle room or ensure the furniture, doors, or aesthetics work. The trick is to get this right before the install as it might cost you more if changing during the install. Your engineer should be able to help you with these design changes. It is sometimes better to pay just a little more for a different radiator or for a change in pipe work than live the next 20 years walking around a radiator specified in the wrong place.
The install was down to take 4 days. Writing this article I am trying to persuade people that ASHPs are great and everyone should have one however I would be lying to say the install is not stressful as your house is invaded by an army of tradesmen, plumbers, electricians, refrigeration engineers and delivery men etc. I know some people hand over their keys and go away for the week and come back when all is done. Although it avoids the noise and the stress there are always decisions to be made on how high do you want this and what location. I would strongly recommend you be there. I also recommend not inviting guests to stay that week.
The disruption to your life will however not start on the day of the install. For me the week before the install a lot of equipment arrived and was all put in my conservatory. This included a stack of radiators, the tanks and control unit.
Your engineer may have decided that no floorboards needed to come up and no furniture moved however for me I think I emptied every wardrobe in my house at some stage. It gave me a chance to have a clear out. My fuse box is at the front of the house and the ASHP at the back of the house so this also meant there was also a electrical cable to run from the front to the back of the house.
By the end of day 1 my front garden had become a rubbish tip for all of the old radiators. PS: plan to have the system changed in the summer as obviously the heating is off. For some reason when tradespersons (they were all men) arrive the front door is generally left open for the whole time because they are ‘just popping out to the van’. It is just a thing and there are at least two white vans outside for the whole time. Provision of tea and coffee is obligatory and I would suggest copious biscuits as the quality of the job may depend on it. I was working from home so spent my time in between my desk and the sitting room which was stacked up with all that had come out of the cupboards.
The floorboards were up for all of the four days. The ASHP arrived on day 2 and was manhandled into the back garden with lots of swearing enroute by the installers, as I only have steps and a single width path. A few plants were trampled on the way. The ASHP does not need foundations but did come with a 100mm plastic slab to put on my soil to create a base. The ASHP also sits on rubber blocks to absorb operational vibrations. You may want to ask your installer about these items if you want the unit to fit in a particular space or say just be level with your fence rather than peek over to next door.
The electricians arrived on day 3, and the power kept being switched on and off as did the water.
I would recommend microwave dinners as the kitchen was a hub of activity.
By day 4 things were calming down. The plumbers did not completely finish on day 4 but to get things in order came back on day 5 to connect some final thing up, flush the system through and turn it on. They ran though the settings, handed me a load of instructions and a control unit to put on a shelf that connected to my Wi-Fi. Yes, you generally need Wi-Fi.
My front garden was still covered with old radiators, copper pipe and the old boiler. The plumbers said the company would come back and collect. Strangely the company were not local and never came to collect the rubbish. This however was not a problem as a scrap merchant came around, knocked on our door and said he was taking all of the scrap metal. It was less of a question and more of a statement. I then took all the numerous cardboard boxes down the local council tip.
The plumbers ran the install and the system was complete. What the plumbers did not do however was make good the decoration where the new pipes had been poked through, or box in the control unit and new tank. The requirement to box in and fill in holes will be very specific to each house and each system but is a consideration when planning the location of the units and radiators.
If you are good at DIY or have a handyman this is perhaps not a problem. The installer, if any good, may do some of this as part of the install, so ask the question when getting the quote.
How does the new ASHP perform?
Performance is directly related to the initial design. A badly designed system will not perform as specified whilst a well considered design will do what you want it to. If the installer did not recalculate the radiator sizes but just used the old system and installed an ASHP in place of your boiler, the chances are that the radiators will not transfer enough heat in the room.
The supply of heat from a gas boiler is different because the gas boiler waits for the temperature to drop before heating and potentially switches off a little above the target temperature. This gives a fluctuation in room temperature from a slightly chilly feeling followed by a potential slight overheating. The result sometimes is that people fiddle with the thermostat to give more or less heat which tends to lead to further fluctuation and more overheating. The heat from an ASHP is constant and the radiators don’t necessarily feel hot but the room temperature stays at the constant desired level.
I programme my thermostat at 21 degrees during the day and 19 at night and keep my system on all year around. I also have the Thermostatic Radiator Valves (TRVs) set low in the bedrooms or lower in rooms not used frequently. I also keep all doors closed. The towel rail in the bathroom is oversized to take account of drying towels, does not have a thermostatic valve fitted and provides slightly more heat. The result is that the living spaces are warm and the draughts kept to a minimum. I realise these are my own personal preferences and are not a recommendation but perhaps demonstrate that setting up the system can give options that are partly based on your specification to the installer.
In conclusion we are very happy with the change to an ASHP as the temperature is a constant warm 21 degrees.
Does it cost more ?
I recently saw someone on the TV saying they installed an ASHP for environmental reasons but their electricity bills were 50% higher. I have to say why? This is not the case for my new ASHP system. You should be able to work out your expected heating cost before you install the system. For me I would say that the amount of energy required to heat your home will not change just because you change the system. If you look at your energy bill for say December it will show how many kilowatts of energy you have used. There is however a difference in the price of gas compared to electricity. Electricity is generally 3x more expensive than gas per kilowatt unit but as stated at the beginning of this article, for every unit of electricity in supplied to an ASHP you get three times as much heat out. The result is that they should be about the same cost. One observation I would make is that my system also provides hot water and this is an additional power demand. If you do not use this hot water and continue to use your independent electric shower your bills will go up as you are using additional electricity for your shower and not using your tank of hot water. I have also changed my shower to feed from the hot and cold from the bath into a mixer tap making my electric shower with direct feed from the cold water redundant. Note the ASHP hot water supply to the hot taps is pressurised and not gravity fed so is well suited to supply a mixer tap.
It is difficult to make direct comparisons using just cost calculations, as units of energy are needed to be accurate for a before and after analysis. My gas boiler was taken out when energy prices were low and so comparisons pre and post energy crisis give a distorted figure. Cost comparisons year on year are also difficult as weather patterns are not consistent.
There are additional ways of saving on your energy bills including insulation, double glazing etc. but there are simpler things like installing thick curtains for windows and curtains for stairs to stop heat rising and keep it on the ground floor in the living spaces, plus, as noted earlier, shutting all of the doors to stop warm air loss from each room.
I have also installed solar panels and a battery. It is worth noting 2/3 of the energy from the solar panels is generated in the summer months when your heating is dormant. This is because of the obvious observation that daylight hours are longer summer v winter plus the sun does not rise so high in the sky in winter to hit your solar array at the optimum angle. Your ASHP power demand will not be met by the solar panels on your roof. A battery however being set to import electricity at the cheap overnight rate over winter will provide energy to your ASHP to assist with daytime electricity tariffs and is a good addition to the ASHP (depending on your supplier and deals/rates on offer). The payback would need to be calculated as this is an economic rather than a direct green objective.
Oh and what about the noise of the system, does it keep me or my neighbour awake at night? The answer is - does your fridge keep you awake at night? It is the same system working in reverse so no it is very quiet. During the day the background noise of the traffic on the road is louder than the ASHP. Check supplier information for each ASHP as they are not all the same and google typical decibel levels for background noise to compare.
One thing the outside unit does is blow cold air out the front so location and activity in front of the ASHP unit are considerations.
As a foot note:
New gas boiler
My father did not opt for an ASHP but for a gas Combi boiler (why not an ASHP, you will have to ask him, but it is sometimes dependent on what you have read and from where). He was changing from a traditional heating system with hot water tank and header tank. The system had a single supply pipe to each radiator and all radiators were old. The system required a full strip out and renew. He got a local plumber to supply and fit. It took 4 days, floorboards needed to come up, cupboards needed to be emptied. Two vans were outside and the front door was open for most of the day. The heating was off for the 4 days and electricity on and off occasionally as was the water. We decided to eat out most days. My ASHP system cost me ½ the price compared to my dad's although I did get a subsidy and my dad did not. The plumber took away all of the old radiators. I made good of all of the old and new holes throughout the house.
He is very happy with the system! He is still trying to find the best place for the thermostat as the house heats up and cools down.
1. https://www.gov.uk/browse/housing-local-services/household-energy