Air Source Heat Pumps

General Discussion Forums Life, The Universe and (almost) Everything!
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Can anyone share their experience of converting from a fossil fuel boiler to an air source heat pump for their house?

Not looking for a slagging of the technology because it will work in a modern thermally efficient building where a passive heat source provides enough output to maintain a comfortable living temperature.

I’m thinking more where a building is partly old and stone built though where the parts that can effectively be modernised and insulated have been, though not approaching overall anything like a modern energy efficient build and currently heated by an oil condensing boiler with an efficiency of 96%.

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I’m not going for slagging off the tech… The only experience I have is, friends had a brand new eco house built with all the full insuiation, solar panels, battery storage and an air source heat pump. They find it struggles to keep a good temperature in the winter.

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My heating engineer said that unless you have a fairly modern house or one with excellent insulation and air tightness it wouldn’t run with great efficiency and we would be left wanting, it also necessitated a seperate electric means of constant hot water (megaflo cylinder). We went for a new Worcester 8000i gas combi and a whole new system on our 1960s house when we bought it. Also it seems a lot more invasive to install than 22 and 15mm copper or plastic pipework (we went for copper).

I also looked at ultra efficient eco new builds when we were moving that had heat pumps only and no other source of heating and the people that eventually bought were using portable heaters to get them up to temp as they can’t generate heat, only extract and return it to the house.

I’m no expert and I’m sure they have their place in an efficient home, but it’s a gamble I didn’t want to take on ours. :+1:

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They tend to work best when used with underfloor heating rather than radiators. Your basicly storing the heat in the concrete slab and the trickel of heat is enough to top it up.

I work for a company who install them, although thats not my job in the company. The uptake is low due to instillation cost as well as the increased cost of running them.
The tech will get better as many companies invest in the development. But the new to me house i just bought is having underfloor heating installed along with a new oil boiler. The cost of a heat pump plus the upkeep just to me dosnt add up at the moment. That incluseds a large discount i get from the company i work for.

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Good feedback all, thanks.

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Lol, sounds like storage heaters, we’ve gone full circle! :wink:

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I thought that, also I’m always very wary of anything that has a government incentive to get people to buy in, generally things that are genuinely better stand on merit and don’t need any type of coercion or incentive for people to want them. Just my opinion.

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My brother is a Warrant Officer in the Fleet Air Arm, basically 30 years on helicopters. He’s recently done a DIY install on his 1940s house. He’s very happy with the outcome. It was a learning experience. Basically, his thoughts are the industry is full of cowboys who don’t understand what they are installing, and that is the reason for the bad reputation. They’re generally the same mob who will sell you a kitchen or windows.

He’s planning to get into it when he leaves the Navy in the next few years, but more from the perspective of checking and signing off installations.

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My house has used an air-heat-exchanger (made by Rega Ventilation, sold by Wickes, heavily modified by me) since the mid 1970s, and depending on temperatures it can recover up to a kW from out-going stale smelly wet air (eg from bathrooms and kitchen) and put that back into incoming pollen-filtered clean fresh air from outside going to bedrooms and living room.
It allows the windows etc to be shut all year, a big plus to keep out dust, burglars and mossies etc.
Its two fans use about 30W. It will be cooling in summer since all it can do is maintain a status quo but eventually temperatures will climb. This is when I switch on the air-con.

The air-con is air-source heat-pump, an older version of this Electriq. It has a gain of between 3 and 4 depending on mode cool or heat.
It will cool the whole ground floor in the hottest summer.
It will also warm much of the house, but only until the outside air temperature goes down to about 8C. Below that the outside ‘radiator/collector’ can tend to ice-up. Apparently the thing then can turn on an electric heater! But by then we are on the normal condensing gas.

Alas, until air-source heat pumps can overcome their icing-up problem, here in the UK they will never be viable without supplementary heat.

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I posted a similar question on another forum a while back. Whilst I asked for comments from those with actual experience, the majority of the replies were from people telling me what they thought / had read.

With that in mind, I held off replying for a while. The reason being is that whilst we have explored air source and obtained quotes, I can only pass on what were the key reasons for not proceedings……but for what it’s worth:

Our first quote, from a local company, were basing the setup to run at 18 degrees 24/7. Everyone is different, but to us, that’s too warm overnight, marginal during the day and too cold in the evening. Cranking up the thermostat by a degree or too would address the day / evening, but not overnight.

Our second quote was from Octopus Energy. Initially, micro bore piping to the radiators was an issue but they now deal with that via some widget that is obviously an extra cost. The most significant thing I learned from this quote was that TRV’s cannot be used on individual radiators - apparently it throws the system out in some way.

In summary, running 24/7, producing a constant temperature that may or may not be appropriate at certain times to all rooms seemed inefficient.

Our house is a 2003, well insulated detached property.

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I looked at this in great depth, as I have no mains gas.

There are a few things thet don’t tell you when trying to sell you one.
they don’t add in maintenance charges.
They don’t tell you that you will use large amounts of Electricity to boost the temperatures, as the hot water runs at 50 degrees and you need to get over 60 degrees to kill legionares bacteria.

After doing all the calcultions and a similar calculation for Propane, I have an Oil fired boiler!

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This is another interesting problem.

That old stone is a fantastic heat/cool store with a very long thermal time constant, but only if you can apply the insulation on the outside of the house where the weather and temperatures are all over the scale.
But what effective cladding can you apply that the Council planners etc will approve, and that will be resistant to vermin, ants, etc, and be fireproof, and be attractive, and be weatherproof, and be affordable.

I’ve insulated the whole ceiling of our ground floor, this allows the bedrooms above to be much cooler say about 16C, comfortable for sleeping, whereas the living room, kitchen etc below are 20+.
Before insulating those ceilings, a well insulated loft resulted in the bedrooms being hotter than downstairs!

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The stone is granite blocks and up to 2 - 3 ft thick in places. Interior is lath and plaster, unfortunately there’s not that much we can do that’s not a massive exercise. The ground floor in this space is concrete and not the modern kind in the rest of the house with masses of insulation. We might be able to put a thin layer of insulation on the floor under carpet/plywood and reduce the height of the doors which are scheduled for replacement anyway, I have heard good reports around insulating wallpaper too.

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We’ve had an air source heat pump for 9 years.
The original gas fired boiler fed a radiator/microbore system (still in use). It provides plenty of hot water, only using an immersion heater, once a week, to combat any legionella issues. It operates on a :arrow_up_small:t of +25°C, which is approximately ½ that of a gas boiler system, hence th he need for improved insulation. We are happy with it’s operation for around 90% of the heating season, using a wood burning fire and bioethanol fire in the coldest weather. With solar panels (installed 11 years ago) our cost of heating and hot water was paid for by the government FIT payment, until the energy rates went through the roof. As a retrofit system the performance and the cost of running the system is acceptable, providing solar energy is available to power the ASHP.

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This is precisely the problem most of us in older properties face!
Often, it is almost cheaper to knock it down and start again!

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Long answer but might give you some idea and possibly debunk the idea that heat pumps are never any good.

Your stating point is probably a proper heat loss calculation. Your current energy usage should cross check broadly to this.

We recently (Apr 2022) moved into our new self-build which is a 2 storey house with 213 sq.m. heated area. Our energy certificate is B (84). From memory our heat loss calculation was about 6.5kW.

We have an 11kW Mitsubishi Ecodan air source heat pump with the pre-plumbed 300 litre hot water cylinder.

In the 12 months to the end of October (yesterday) our total electricity usage was 8,825kWh, cost before support payments was £2,595.

We only use electricity.We keep our living space and bathrooms at about 22C, bedrooms 19-20.

From June-Sept the heating was off. During that period we used c. 400kWh per month, so I can infer that over the year about 4,800kWh of our usage was not for heating. Therefore our heating cost for a year has been 4,025kWh costing pro rata about £1,200. The heat pump still runs in summer for hot water, I reckon it uses 2-3kWh per day for that.

The new build replaced a draughty 1951 bungalow with about half the heated area. I looked up our old bills and in 2017 or 18, I can’t remember which, we had used 7,000kWh of electric and 27,000kWh of gas. (My wife liked using the conservatory in the winter where she used direct electric heat. The rest of the house was heated by the Potterton boiler built into the gas Rayburn). 34,000kWh to <9,000Kwh and a house double the size? I’m happy with that.

For completeness we also have a Vent-Axia MVHR (mechanical ventilation with heat recovery) unit which pushes filtered air into the rooms we live in, and extracts it from the kitchen, utility room, and bathrooms, via ceiling vents. It recovers c. 90% of the heat from the exhausted air. It moves a houseful of air about every 2.5 hours, practically silently - I can hear it in places in the dead of night. It manages humidity very well, any bathroom condensation disappears in less than half an hour without using a noisy extractor.

We have a decent level of sealing. There are no window vents or airbricks, so no draughts. We have a back-up solid fuel stove which has its own piped external air supply so doesn’t need a hole in the wall (and doesn’t unbalance the MVHR)

Space heating is underfloor both upstairs and downstairs. Heating (except when off for the summer) runs 24/7 as need.

A point to note is that a properly sized heat pump does not have the same capacity to bring a house up to temperature as an average gas boiler. Our 11kW (we could probably have got away with 8kW) basically balances our heat loss. OTOH an average gas boiler in a 3 bed semi with half the area will typically have a 30kW boiler. So turning off the heating while the occupiers are at work and reheating it from say 4pm is quite doable. I can’t do that. When cooler weather was forecast in early October, I put the heating on a couple of days before. It will stay on until next May.

Retro-fit is another ball game. My flow temperature is typically low 30s. The floors don’t feel warm (they aren’t clap cold either) because the circulating fluid is below blood temperature. It works because, in effect, we have very large radiators, being the floor area.

You would probably use flow temps of maximum 50C with a radiators, so if you are coming from gas or oil with a boiler temp of 60-70, you’ll probably need bigger radiators in some rooms. The higher flow temps will still hurt efficiency. If the system is old, pipework might be inadequate.

I realise this is not your situation but some things are common. Insulation, to make the heat loss manageable, and sealing, for the same reason.

Edit: I should have said we have no solar PV/battery. Three reasons for that, I didn’t know that electricity was going to be 35p per unit, the only place sensibly to put it is the front roof, so unattractive, and we are unlikely to live here (or maybe just live) long enough to make a profit on it. But, long term, it is obviously now a good idea.

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Another thing to consider which isn’t a popular subject but one worth bringing up - age. I live in a street with a LOT of older people and families, and regularly see and hear about people in their late 70s and onwards installing new triple glazing, paying for cavity fill, solar panels and new heating setups. I’d never interfere as people can do whatever the hell they want, but I wonder how much consideration is given to how long the improvements will take to pay for themselves and whether or not they’ll be around long enough to reap the benefits.

A friend of mines grandfather likes to keep busy and have things going on. He recently tore apart his otherwise liveable bungalow and installed warm roofs, gunned up the floors and retrofitted celotex and underfloor heating, clad the internal walls and ceilings with pir and had them refinished, new windows and doors etc and then renovated the whole place. I think he is in his early 80s.

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FWIW my hot water is set to 48c, part of the reason for having a big tank. The legionella setting raises the temp to 62C for 2 hours once every 3 weeks to kill any bugs.

I have a separate meter for the immersion heater. When I checked, I think each legionella cycle used about 6kWh. There would be some saving on heat pump units so I estimate the legionella cycle costs us maybe £30 a year.

TBH I doubt we even need it. It’s a pressurised system so there’s no dead pigeon tank in the loft. I don’t see how legionella would get in. I run water through the unused taps and shower heads once a month to flush out anything lurking in there.

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Hi Ian

I bought a 1950s semi detached at the start of 2021 which had an old gas combi boiler that needed replaced. There were an assortment of radiators which didn’t work well plus a gas fire in the living room that was needed to boost the temperature. The house has a large south facing roof (located suburbs of Edinburgh) so I decided to install solar panels with an air source heat pump for heating/hot water.

The system works well. I have underfloor heating on the ground floor with 2 radiators in the upstairs bedrooms. I topped up the loft insulation to modern standards and replaced the gas fire with a wood burning stove.

I would say that it is difficult to get an installer that really knows what they are doing and there are some scary companies out there saying they can install your system in 2 days etc. It really pays to talk to lots of different companies and find someone that knows their stuff. It all depends where you live but one of the reasons I went for a woodburner as a back up is that there is the possibility of power cuts and that is more of an issue in rural areas.

You can have a great experience or you can be disappointed. ASHP’s are relatively new technology and that is a real issue as most heating installers are still primarily working with gas or oil.

If you want any more info send me a DM.

Neil

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Thanks all for the feedback so far, I’m carefully looking at different options and any change will not be a quick decision.

We have south facing roof space suitable for about 2Kw of panels, if we had the garage roof replaced (cement/asbestos board) then we could probably put 6Kw on that which might be an interesting proposition.

We have a relatively recent (7 years) Grant Vortex external combi boiler and as part of the renovations we had done at that point removed the central heating header tank and also the hot water tank. Finding space for an hot water tank will not be straightforward and would probably mean building an external housing for it.

We do also have a solid fuel stove as power cuts are not unknown here either and with the seemingly greater energy in weather events may become more common again.

I was not aware of hybrid oil/ahsp systems which look quite interesting.

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