Hi @chandykris and you're very welcome here.

Let me turn around the way in which that 14kW figure is expressed.

The heat pump is sized according to the amount of energy which your houses loses to the outside air.
That's a static figure based on the insulation characteristics of the building's fabric.
It remains the same whether you use underfloor heating (UFH) or an IR radiant heater.

Posted by: @chandykris

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My primary concern if we go for a 14 KWH heat pump and run for the whole house (without zoning etc), our carbon emissions may just go up rather than down.

That's fair comment, but once again the phraseology you are using doesn't match the way in which a heat-pump should be installed.

"Zoning" is how you'd exercise control if your heating source was capable of putting out more heat than the home requires.
When thermostats in each zone reach the desired temperature, then the heat-source (boiler) is turned off.

But a heat pump shouldn't ever be receiving a signal to turn off.
Cycling on/off is inefficient. Your COP (coefficient of performance) will be decreased accordingly.

The way in which a house with a heat pump is governed, is to balance the emitters (radiators or UFH).
Instead of each emitter having a thermostat, the flow-valve (radiator lockshield) is closed down to the level that allows heat to be distributed evenly.

You may not even have emitters on the upper floor.
In some cases it's adequate to allow heat to rise from below.

To appreciate what the rival quotes mean we need to
a: change the way we think
b: study the energy loss figures for each room

You will obtain more useful comments here, the better you describe the house.

Knowing the total floor area would be a good start!

Thanks @transparent. The heat loss was estimated at 11.86 KW by one installer. They had made minor errors such as classifying the property as a pre-2000 built house. Ours is a 2013 built, 200 square metre house, cavity wall/underfloor/loft insulation and double glazing throughout. Maybe the 11.86 KW figure is an overestimate. Plus the installer designed at 55 degree flow temperature and using a buffer tank, with a 3.4 SCoP. I just assumed that they know what they are talking about.

I wonder whether it's just bad installers giving quotes that are not suitable to the house. Another installer just looked around and came up with the figure for the air to water system, rather than doing a thorough heat loss calculation. This same installer also gave a quote for an air to air heat pump for two of the rooms. It was designed as a split system with one outdoor unit, one 3.5 kwh indoor unit for the open plan kitchen living dining and a 2.5 kWh for one of the living rooms that we use throughout the year.

Maybe, we should get an estimate from a proper HeatGeek approved installer before deciding which way to go.

@chandykris

I believe that your home heating system should be capable of supplying the needs of the whole home, independent of the actual number of occupants, particularly if you wish to take advantage of the BUS scheme.

Having said that, have you considered a combination of Air to Air (A2A) heat pump (Air Conditioning that also heats as well as cool) along with radiant heaters in rooms where the A2A may be too noisy.

While you will not be able to get any form of grant, A2A is much cheaper to install than Air to Water (A2W).

Thanks @derek-m  

I wasn't originally considering A2A. But, one of the installers recommended this option, exactly like you have mentioned. Their A2A design was to install a split system for the two of the living areas, and IR heaters for the bedrooms. I started looking at A2A, and found some very interesting videos about A2A from EV Puzzle and Tim & Kat's Green Walk on YouTube. Both highly recommend their A2A systems, so definitely one to consider.

We want to pick one option and install before the heating season starts. Hoping that we can come down to 500 kg CO2 emissions figure for home heating.

I installed a small A2A unit at our home some time ago. It serves two purposes, whenever sufficient solar PV generation is available it provides totally free heating to supplement our gas boiler, on the occasional hot Summer days it also provides cooling, again totally free since it is supplied by solar PV power.

A further benefit of A2A is that it warms up a room much quicker than an A2W system, since it heats the air directly, and I believe may be more efficient.

I think there are systems available that have 1 outside unit feeding up to 4 indoor units, so can cover quite an area. The indoor units can be controlled independently, so not all the rooms have to be heated at the same time.

One drawback is the slight fan noise, the other is that the system cannot heat DHW, though hot water cylinders with a small integral heat pump are also available.

When looking at units look at EER and SEER figures, they vary quite a lot. EER is for cooling what CoP is for heating.

I have a spreadsheet my old phone looking at a lot of A2A and compared performance. Will dig it out and post

Spreadsheet 

@chandykris Im late to the party here, but from your description of the property, a 14kW heat pump seems rather large.

Using the heat geek cheat sheet a post 2006 new build should have a heat loss of 20-40 W/m2. At 200m2, your houses heat loss should come in somewhere between 4-8 kW.

I too use an A2A ac unit in my kitchen and it is useful, however if I were you I would get a heat geek in to assess your home again as the figures dont ring true to me.

Thanks @bontwoody 

Yes, I was surprised too, definitely the case of an installer who doesn't understand heat pumps well and looking to leverage on BUS grants without upskilling themselves.

On days like today, A2A system in the kitchen sounds like bliss! Especially with all the solar production for the past four days.

Definitely would get a HeatGeek to do a heat loss survey, probably Urban Plumbers work in our area too. 

@chandykris 👍. They should sort you out. I’m very impressed with Szymon‘s videos. 

@bontwoody Got a desktop estimate of 10 KWH heat pump from Urban Plumbers. Based on the house current EPC, size, age of the property etc. They would have to do a full heat loss survey to confirm though. This sounds more reasonable and avoids oversizing/cycling, I would think. Got to decide soon whether to stick to my original plan of testing with IR panels, or switch to heat pumps. In a way, I can't wait for a slightly colder day to test the one IR heater we installed recently.