So much for no more boilers!

[PeterC]

Refurbished hotel took out electric heating and DHW to use gas instead. Check the figures etc.

[wasbit]

The link was so good you named it twice. Even so it might wrap.

[David Wade]

After the current price hikes, heat pumps would probably have been more economical.....

Dave

[Tim Lamb]

Hmm. We had 4 dwellings constructed in our old grain barn (2020). The plans showed air source heat pumps. In the event, the existing electricity supply was considered insufficient. An 11kV transformer too expensive and the housing is heated by mains gas!

[NY]

Do air source heat pumps actually work? Do they actually get the house as warm as radiators heated by gas or oil can do?

I ask because my parents had a house that was heated by ducted air and a) it was always bloody freezing, and b) the house was always dusty because of the dust that the ducted air circulated.

When we were looking for a new house a couple of years ago, we saw one that had air source heating installed by the owner who was a heating engineer. He raved about the heating system, but there were cold draughts in every room and an inescapable whine permeated the whole house.

In the event the house that we bought is heated by gas boiler and radiators, plus a gas Aga in the kitchen and (for the evenings) a wood-burning stove in the lounge using free wood from all the trees we've pruned. It's costing a lot more than it did before the gas prices went up, but we've reduced gas consumption by turning the heating down a degree or so, and we keep room doors closed and don't heat the corridor outside the rooms. Our economies have reduced the daily gas usage from 5 cubic feet (2021) or 5.8 cubic feet (2020) to 3.5 cubic feet (2022) for March. So far, we only have comparative figures for March because we didn't start the economies until the end of February this year.

We'll notice a bit of an increase in overall cost in a year or so's time when we don't have as much of our own wood to burn: there was a lot of pruning and removal of trees, and that wood has been seasoned and used in rotation, but we probably won't be cutting much more down now so what we have will gradually be used up.

[NY]

If it was a new house, where the air ducts, the hot water heater, the heat exchanger box etc could all be designed in before construction, an air-source heating system might be feasible, though I'd probably want a Calor gas heater and cooker hob in reserve, just in case of power cuts - the problem with going all-electric is that you are putting all your eggs in one basket.

But retrofitting ducts, boiler, huge and unsightly heat exchanger fan in an existing house (some of which dates back to 1800s) is not affordable. It so happened that we did need a new boiler shortly after we moved in because the hot water cylinder developed a leak and the engineer discovered that the boiler was about to corrode through, so we went for combi boiler heating water on demand rather than heating a cylinder of water. But the crucial thing was that it used all the existing radiators and CH/HW piping. So the disruption was confined to the boiler room and the airing cupboard where the cylinder had been.

In hindsight, would we have been better off going for oil rather than gas? Well both have increased in price dramatically, but hopefully things will get back to normal eventually. And at least it works, without cold draughts, dust and a godawful moaning whine through the house. And no unsightly and throbbing fan-box bolted on the outside of the house.

If a ground source / air source heating system could heat water for conventional radiators, then it might be worth considering. But my experience with my parents' puny ducted air heating puts me off that technology (how ever the air is actually heated).

[Theo]

Yes and no. Work they do. They don't get *as hot* because boilers output water at say 70C while heat pumps prefer 45-55C. You can make them hotter, at the expense of efficiency. But it's much better to run them at lower temperatures to make them more efficient. That means larger heat emitters.

Basically you *can* drop in an ASHP for a boiler, but the efficiency is worse than doing a proper system design. Given lack of efficiency will cost you over the lifetime of the unit, it makes sense to get the design right to begin with.

Replaced a 14kW boiler with a 13kW ASHP, house is just as warm overall - the ASHP doesn't actually need to work very hard. We did upgrade the radiators to cope with the lower flow temperature, and the installer failed to balance them so there was some unevenness between the rooms. After 3 months they came back to fix their (numerous) mistakes, although we now can't test that until winter.

That's an air to air heat pump. With an air to water version the radiators are silent, just like boiler rads. The outdoor noise is quieter than the old boiler, although more continuous.

Our water ASHP also does cooling (down to 7C). It works very well, but radiators aren't good 'cold emitters'. I'm looking at fitting fan coils.

Our ASHP takes 2-25 kWh per day, depending on the outside temperature. In March usage was average 10kWh per day. That includes hot water of 1-2kWh.

1 cubic foot of gas is 0.29kWh, so your 3.5cuft is roughly 1kWh. Given the Ofgem average heating load is 12000kWh per year, I'm a bit dubious about your numbers. Do you mean cubic metre? (10.55kWh)

Theo

[Theo]

Air sucks as a heat transmission medium, because the specific heat capacity is so low. That's why you need to blow a lot of air to get much heat transfer. Lots of blowing = noise, dust.

Water has a much higher specific heat, hence it's much easier to install pipework. Convection can be silent, whereas transferring heat by conduction usually needs forced movement.

Heat pumps can use either. Each have their pros and cons, especially if you want them to do cooling as well as heating.

With oil you need a 1000+ litre oil tank outside of the house, so I don't think that wins on the unsightliness. We've actually regained a good chunk of garden by removing our oil tank.

They can, and they do.

Theo

[The Natural Philosopher]

An air source heatpump certainly can work, but you need to understand its inhernet limitations

Firstly, it is at its most efficient when raising temperatures by the smallest amount, So you can get out up to 4:1 more heat than dierect electrical when you are heating water from say 5°C outside to say 40°C water temperature.

However that raises further issues

- that water temperature is well below what any conventional gas or oil boiler can deliver, so a one for one replacement will be hopelessly inadequate. You need larger areas to radiate sufficient heat at 35°C compared with radiators at 50-60°C, so in order to use the pump to its greatest efficiency, you will need to install underfloor heating, most likely. And the attendant insulation. I.e its a pretty hopeless choice for an existing building upgrade...

- the water temperatture itself depends on there being external heat to pump. If it goes below zero outside - air temperature wise - that heat pump will struggle. Like all 'renewable energy' technology it lets you down when you need it most.

Ground source pumps are better - the soil rarely freezes at depth, and there is a far greater thermal store to tap than there is with air source.

- because water temperatures are typically too low for a domestic hot water system most air source heat pumps add in immersion heaters to raise the DHW temperature enough to sterilise it and make it usable. They often will add those immersion heaters to the heat pump output for room heating as well, which reduces the overall efficiency of the heat pump just when it needs to be outputting its maximum - especially if the heat pump is cheap and undersized - leading to almost no pump gains at all and a shocking electricity consumption under very high output conditions in very cold weather. Ground source pumps are generally better in this respect.

Scandinavian houses seem to use direct electrical heating or ground source. Go figure.

Air source means the heat pump sources heat from the air outside,m it doesn't determine how it is delivered inside. Hot air blowers are very very good done well with air filtration. Think local supermarket, where refrigeration of the chill cabinets allows heat to heat the building to be recycled as hot air curtains and the like. .

I would stick with what you have.

Gas prices will stabilise, and until we go fully nuclear electricity will be very expensive .

[Tim+]

But not necessarily your existing radiators (which I think might be what NY is on about)

Tim

[Andy Burns]

Depends, keeping radiators with an ASHP (air to water monobloc) is not ideal as the efficiency goes down with higher flow temperature, adding UFH with lower flow temperature usually not practical, alternatively you could use a split system with internal wall or ceiling mounted fancoil units

ASHP certainly doesn't mean switching to ducted air heating

certainly there's a lot to get right, and it makes more sense for new builds rather than refits

[Andy Burns]

Is yours a monoblock or split system?

I can see it would be possible to "tap" off the refrigerant loop with the latter, to feed fancoils, but do the former allow it too?

Did you get any grant for fitting yours, I though it was verboten to have cooling if fitted with a grant, or have you "hacked it" to add back cooling functionality?

[Clive Arthur]

<snip>

We've stayed in several National Trust cottages with ASHPs in winter, and they were very comfortable. The ASHPs were big and they certainly looked expensive, plus there was top up with immersion heaters and backup with logs.

Mind you, with the amount the NT charges, they could be made from gold.

My sister has a GSHP, but it's a new build/renovation so plenty of opportunity to do it right. Not finished yet.

[She also has solar panels and a windmill. Her husband is a scientist in the nuclear power industry. Oh look, an exploding Turnip!]

[Theo]

Monobloc.

The water comes out at 7C, it goes around the loop which happens to go to the rads, so they get cold... (and damp, given condensation)

Currently it's set up on a conventional boiler controller, so I have to wind the thermostat 'up' (calling for heat all the time) to start the ASHP and run the pump, with no thermostatic control (the TRVs need to be set high enough to open to begin with). The ASHP has its own controller which knows how to do heating and cooling sensibly, so I'll likely switch over to that.

Haven't worked out how to plumb it yet - thinking something like an UFH manifold (but with a higher flow rate) with an insulated pipe to each fan coil, and the whole lot on a separate zone. The ASHP supports two zones with a slave controller (which I have), but I likely need to work out how to do room thermostats too.

Cooling isn't forbidden on the grants (it previously was), it just has to be metered separately if you have multiple heat sources and you're getting RHI based on usage.

My ASHP does not officially offer cooling, but I found a way...

Theo

[Andy Burns]

Wouldn't you get more cooling by using the vapour loop, instead of the water loop? Then have an "aircon like" unit in selected rooms?

[Theo]

The vapour loop isn't exposed on monobloc units, so you'd have to tear the thing apart. It goes straight into an internal plate heat exchanger, on the other side being the water loop. The fan coils are simple cold-water-in, fan blowing room air across fins, warm-water-out.

I suppose you would get better heat extraction by using the vapour phase, but you'd have to run refrigerant piping everywhere, and the vapour loop might run less efficiently (being longer and potentially with multiple branches and valves depending on which rooms wanted cooling). The risk is you compromise efficiency of heating for the few days a year you want cooling.

Theo

[Andy Burns]

That's what I was asking about, whether it was possible to "get at" the vapour loop on a monobloc, rather than just the water loop ...

[newshound]

Perhaps you need to put the electric heating on the input air too :-)

[Andrew]

Friend nearby did this about 12 years ago. 8 rads replaced with triple-panel ones but the Samsung ASHP was sited at the back of the house near to the existing gas boiler which was disconnected and faced North, which I suspect lowered its effectiveness.

I asked her how good it was in winter and she said she was cold all the time !, and they had to keep on burning logs on an open fire (chimney added retrospectively in about 1985 to a 1972-built detached house with the upper part of the south facing front clad in shiplap timber over a 'solid' 9-inch block wall (blocks actually have two large hollows).

Apart from loft, cavity and double glazing, no other insulation and if typical of other houses on this estate, massive air-leakage through all the gaps in the blockwork hidden behind cladding or soffits/facias.

[newshound]

In around 1970 an old boss (a very good engineer indeed, now an FEng) bought a "plot and shell" from the developer of a small estate and DIY'd and subcontracted all the fixtures and fittings including plumbing and electrics. He went for a central "heat store" on Economy 7, and ducted warm air, plus what were very high levels of insulation for the time. Probably still the most comfortable house I have ever been in.