Heat Greek vs Skill Builder mainly heat pump, but some reference to condensing gas boilers.

[robinbanks]

I've never seen a heat pump

Look like every aircon unit in every film you've ever watched

I can't see how they are cost effective

My system cost me 5 grand, and the RHI paid me 7
I can't see how that's not cost effective!

Can you get someone to fix short notice?

I called Vaillant out once, circulator pump issue fixed under warranty

How reliable?

I've never touched it. "Servicing" it amounts to washing any crap out of the vanes. Never done that either. Been churning out warm water for 8 years now

Saving worth the cost of installing?

I don't have gas. Monobloc systems can be mostly DIY installed and maintained. Overall I'd estimate mine's been cheaper to run than a gas boiler

I was thinking "passivhaus" standards.

Then you don't need a formal heating system at all, and certainly not one as expensive as an HP. Keep a couple fan heaters in a cupboard

Insulation does not have to be particularly good

Insulation should be particularly good in all properties and (in tandem with straight proofing) should be the primary focus of any upgrade, not the heating system

If you get the insulation right you don't need heating, and both wallet and planet thank you ongoing

 

[omph]

There are some tables out there, but at 40% humidity we humans need a stable air temp of 17.6 c to feel comfortable and at 65% we need 19.7c.

The colder the air temp the lower the humidity i.e. cold air holds less moisture. This means body sweat can evaporate more easily. Increased humidity means less evaporation and thus it is harder to cool down. Since the focus is to stay warm during the winter then surely you want to increase humidity and lower evaporation, not increase it ?

 

[RandomGrinch]

The colder the air temp the lower the humidity i.e. cold air holds less moisture.

I'm afraid that's not quite right.
Yes, cold air can hold less water (vapour) than warm air; but that means for a volume of air that contains a certain amount of water vapour, the cooler that air volume gets, the higher the relative humidity will become.
I.e. as cooler air can hold less water vapour, the quicker that air will become saturated.

So as Martygturner says...

There are some tables out there, but at 40% humidity we humans need a stable air temp of 17.6 c to feel comfortable and at 65% we need 19.7c.

If you can lower the relative humidity sufficiently; the temperature we need to remain comfortable doesn't need to be so high.
There are RH limits though, some feel more comfortable breathing in an atmosphere with a slightly higher RH.

 

[flameport]

That's as may be, but assuming you gain an extra 25% efficiency on a £800 yearly gas bill, how long before your new plumbing and radiators pays for itself?

Never.

No heating system can 'pay for itself'.
Heating a building is a cost, both for the initial installation of the equipment, and ongoing fuel & maintenance.

If there is a working heating system, then keep it until it needs replacement.
Then when replacement is required look at alternatives such as heat pumps, rather than just shoving yet another gas boiler in.

 

[omph]

as cooler air can hold less water vapour, the quicker that air will become saturated.

This is the bit that stumps me. 17.5c is uncomfortable for a lot of people regardless of humidity. 17.5c will never feel like 21c regardless of moisture levels.

But the other problem is that @ 17.5c, as the air becomes more saturated it's no longer @ 40% humidity. I had a PIV with 45% humidity @ 18c, I was still very cold.

I would be interested in seeing any materials that will go into more depth. Its an interesting take and I am interested in learning more.