Heat-pump vs condensing boiler

I am dubious I remember too many wonder solutions to save money / energy which turned out to be scams. The principle is the same as a fridge but with the cold bit being outside so you cool the outside and transfer the energy/heat inside but anyone who keeps a freezer in an outbuilding should know unless you get the right freezer it doesn?t work well in winter as a neighbour discovered. The same neighbour has a huge defunct solar water heating system on his roof. It cost a fortune and never worked properly his wife was always complaining about cold showers.

Underfloor Heating is wonderful to live with but bloody expensive to run a friend has it but dreads the bills. We visited when they first moved in and it was glorious but next time we needed thermal underwear and were given blankets in the sitting room after the first bill.

I am getting lots of adverts on my FB feed at the moment (probably because I clicked on the first one) pushing Air Source as a way to save up to 80% of my Oil costs.

I presume the idea is to fit Air Source such that it provides some heat until to the conventional system until it runs out of steam and then the oil boiler fires up to "top up" / take it to the required temp to run the existing rads & cylinder.

but I've not investigated further, as that would doubtless need a visit from a "Surveyor" (Sales Reptile).

Did you get taken in by that one?

UFH is just a big radiator. Like any radiator, it's up to you what you connect it to.

Electric UFH is just a big electric resistance heater, and unsurprisingly that costs to run. Wet UFH can be hooked up to a boiler or heat pump - the latter can run more efficiently due to a lower flow temperature.

With any UFH, if somebody installs it with no insulation underneath you're heating the ground not the floor. That's a faulty installation.

Assuming minimal losses to the ground, the heat flux from wet UFH should be the same as radiators and so the efficiency roughly the same.

(although I don't know how the boiler copes with a mixed UFH/radiator system

- I assume the UFH isn't going to run at radiator temperatures? Is there a thermostatic mixer?)

Theo

First rule of thumb: ignore all Facebook adverts

That's a hybrid heat pump:

A HHP might make sense in some cases, but I suspect they fail to account for the installation costs (even after grant).

There are plenty of legit firms out there to enquire of, although with the GHG they're quite busy at the moment.

Theo

nice to see he is cheap like me....tee hee

There was a heat pump system advertised a couple of years ago that took the heat from "exhaust gasses". All right if you live in a laundry or restaurant kitchen, but most people keep their windows closed in the winter, with minimal ventilation.

Needless to say it cost a fortune to run. Testimonials boasted "toasty warmth" and "piping hot water" without mentioning cost.

Those are designed for super-insulated new-build small flats/houses, where you have heat generating sources (appliances, people, bathrooms) but need to change the air. Ordinarily people would crack a window, but these new builds are highly sealed and so they have active ventilation. The warm/moist/smelly air goes out, fresh air comes in. In a normal MVHR system you just have a heat exchanger to transfer heat from stale to fresh air. In these exhaust air heat pumps (EAHPs) they heat exchange, but also use a heat pump to pull more external air and raise the temperature of the fresh air beyond that of the heat exchanger. Because the place is well-insulated, it doesn't need a lot of heat input to keep equilibrium.

The problems are that the heat pump only works to a certain output. Beyond that there's only electrical resistance heating, which costs a lot. Some systems silenty fall back to resistance mode without it being obvious.

When can happen is if the place is too leaky (eg the householder opens windows or the ventilation ducts aren't properly installed), or the heat pump is undersized, it falls back to resistance mode and the bills are high.

Really heat pumps need massive insulation to reduce heat loss and ginormous radiators or UFH or in wall pipework. That is almost impossible to retrofit to an older house at a sane cost

It is possible to use a heat recovery system to pre heat condenser air,

- you simply have a fixed exit for ventilated air and heat up what is going in with the heat pump

Quite likely in some cases...

As an unqualified statement that is not even wrong.

There is no reason why it should be any more expensive that other forms of heating necessarily. However it does need to be properly installed with appropriate levels of insulation under the heating matrix.

With a condensing gas boiler, it will let you run at high condensing efficacy pretty much all of the time. It can also be a good way of using lower grade energy sources like solar thermal.

If you use electric UFH with no heat pump (i.e. just resistive heating) then it will be expensive, as is any form of resistive electric heating (and unlike storage heating, you can't shift as much to cheap rate prices).

Also consider the choice of floor coverings. If you favour heavy carpet on thermal underlay, then UFH is not a good match. Solid tiled, wood etc floors however work well.

Its works best in places that are continuously heated, since there are usually longer hear up times.

So extrapolating from an example of one, all UFH systems are to be condemned huh?

On 02/10/2020 11:42, Theo wrote: <snip>

There is a thermal mixer on the UFH manifolds but having marginally up-sized radiators in the bedrooms (downstairs/under ground) it's enabled me to run upstairs living area (6 UFH zones)and downstairs radiators all at a max. temp of 55 degrees when it's 9 degrees outside with a reducing boiler temp as outside temp rises.

Might be a different story in "normal" house though.

I'd have thought any heat pump would be wasted if you could not use it to cool the place in the summer. They seem to be on top of this stuff in New Zealand. Brian

If the explanation was too difficult for you to understand then google how they work or stick to cleaning up after hairdressers.

You end up with a warm bum if you sit on it for any length of time. As any undergraduate who has visited friends in St Catherine's Oxford will attest.

They are both Plan A

I have a friend, newish build. His second hand air source pump failled. He was going to buy a new one, £10k, with a life expectancy of 10 years.

We've got it installed in our (downstairs) bathroom. It's not the main heat - it's got a towel-rail-come-radiator - and it's only on for an hour or two in the morning.

Which means we have warm feet getting out of the shower :)

I don't think I'd want to do the whole house like that though.

Andy