Heat Pump: Air-air vs Air-water?

wittynamegoeshere

We've got an old bungalow with concrete floors and no heating system.  It's pretty well insulated, cavity walls and loft all done, but floor not.  Gas is not available.  We're looking to get an air-source heat pump, we don't have enough land for a ground source one.

If we were to go down the line of the classic British heating system using water then either we'd need a duct dropping all the pipes from the loft to the radiator in each room or I'd need to dig the floors up, in which case underfloor heating would probably make most sense, which would probably involve ripping the lot up, digging out and putting insulation slabs in, and I doubt I'd ever recover this sort of investment in energy savings.

I do understand that a lot of heat pumps are retrofit, where radiators already exist, but we have nothing installed already.  Also, for new build, I can see the advantage of underfloor heating as it's completely invisible and very nice underfoot.  But where the buiilding already exists, and the floor is concrete it's quite difficult to install any kind of water-based heating system.

I'm tempted by the idea of an air-to-air system, from what I understand these are very popular in the US and Europe, basically everywhere except the UK.  I'm completely fine about having a box on the wall that looks a bit officey, the other half can probably be persuaded (!), plus this avoids the issue of radiators usually ending up jammed behind furniture and heating the wall instead of the room.  It also means that the pipes would only need to drop about six inches from the ceiling into the unit.

And... the big bonus is that, unlike with radiators, these things can cool the place in the summer if desired, energy prices permitting.  They also seem to cost a bit less.

Is there a downside that I'm missing, or are we Brits just creatures of habit?

Verdigris

You won't get RHI payments or the £5k back on A2A. Beware very cheap units, they aren't economic to fix when they go wrong, which they are inclined to.

I'm in a similar position, although my bungalow has LPG central heating, and I am fitting an A2W heat pump with underfloor heating. You can get reto-fit underfloor heating systems than can overlay the existing floor, so no digging, but you will need up to 40mm taken off internal doors and a similar threshold on external doors. Underfloor heating will ensure the maximum efficiency as the flow temperatures are lower than with radiators. Also it keeps all your wall space clear.

You may find this thread helpful:

https://forums.moneysavingexpert.com/discussion/6240076/i-bought-a-heat-pump/p1

ihatetrump

Is there a downside that I'm missing, or are we Brits just creatures of habit?

Says it all!

Having lived in the US for a number of years in the desert Southwest, heat pumps were the standard method for HVAC - mainly cooling during the long hot (and I mean hot! - 120F to 130F) summers. We never had any issues with them and although it was a few decades ago now, I don't recall utility bills being an issue at the time.

It's a tried and tested technology. You may find this link useful (US Government website):

 https://www.energy.gov/energysaver/heat-pump-systems

Verdigris

I don't recall utility bills being an issue at the time.

Because energy is sold too cheap in the US, which is why less than 10% of the world population contributes 25% to climate change.

ihatetrump

I was hoping to keep politics out of it! (fat chance) and just offer an opinion on the viability of Heat Pumps - hey ho.

If only the answer to climate change was as simple as increasing the retail price charged for energy consumption - can't see China going for that!

Verdigris

I'd worry about the heat losses from putting heating on what I know is a pretty cold floor.  I realise that it will get saturated with heat at some point and stop absorbing it, and some will return to the room after but surely it must take away quite a bit?  There must be a reason why building regs require a thick slab below the floor, presumably your 40mm is around the pipes so perhaps 20mm or so below the pipes?

The losses are about 6% for an uninsulated concrete subfloor. That loss is considered acceptable because digging up the slab and putting an insulated one down would never be repaid in either monetary, or embedded carbon, terms. The 40mm includes the pipework system with a 15mm stone/tile/wood floor on top. That is for a system that runs at 35 degrees, giving maximum COP. You can get thinner systems, that run hotter but are less efficient.

Swan_Valley

It is worth taking a look at this thread:

https://forums.moneysavingexpert.com/discussion/4715287/discussion-ashp-air-air-with-solar-pv#latest

It has lots of useful information & experiences of using A2A Heat Pumps/Air Conditioners.

We learnt a lot from it and now heat our bungalow using 2 units, one in the lounge & one in the kitchen.

As you say, the bonus is in the summer, during a heat wave, is the ability to use the cooling.

matelodave

We installed a PolyPipe overlay underfloor system (other overlay systems are available) on top of a wooden suspended floor in conjunction with an Air Source Heaptump.

Its around 18mm thick and works pretty well. Our bathroom, kitchen and utility rooms have tiles (quite large ones) laid directly on top. The other rooms have carpet. We didn't insulate under the floor although I'm sure that it would be possible to lay high density insulation underneath on a concrete floor

May be worth exploring - Overlay® Underfloor Heating | Polypipe Underfloor Heating (polypipeufh.com)

mrmmhf

Air to air is very underrated in the UK as an option. I love the description by Graham in this video about why people in the UK love to bury hose pipes to heat their homes: https://renewableheatinghub.co.uk/what-is-the-difference-between-an-air-to-air-and-an-air-to-water-heat-pump

Verdigris

There are some carp A2A units about, though. A friend bought two when he needed to quickly upgrade his heating to look after his elderly mother. They've both died in the space of a few years and he can't find anyone to repair them at an economic price.

danrv

I’ve recently fitted Aircon in my property. Toshiba multi split.
Thread here:
https://forums.moneysavingexpert.com/discussion/6269423/7-8k-for-aircon-system/p1