Heat pump vs gas, UFH vs rads?

[Greatescape]

Hi everyone

 

I’d welcome your thoughts please, especially on heating. Wanted to reach out to you all as I’m finding it’s tough to get unbiased advice and personal experience.

 

We’re just about to start a renovation and extension project to a bungalow. The existing building is a time capsule from 1979 with a stunning avocado bathroom suite so we need to do the works: heating, ventilation, electrics, skimming, new flooring etc. So we have a blank canvas.

 

We’re trying to work out the classic air source heat pump vs gas, and UFH vs radiators conundrum.

 

The existing property is 60m2 with a concrete floor (the very fashionable original self-adhesive tiles are below an equally fashionable retro carpet). Ceiling height is c.2.3m. We need to plasterboard the ceilings before skimming, so are losing a touch of height there. The extension will be 30m2. Attic insulation is going to be increased, there’s cavity wall insulation, and we’ll be putting in new windows. We’re looking at installing MVHR.

 

The existing property’s radiators need replacing anyway and the pipes are all currently mounted on the walls, so if we went for rads here it would be a big job including all the pipework chased through the walls, etc. Even if we couldn’t afford a heat pump now, we’d want to make it as ‘heat pump ready’ for the future as possible by using low flow temp rads, etc.
 

Because of the expense of this scenario, we wonder the actual cost difference with the alternative, which is a low-profile retrofit UFH system? I’ve been researching and awaiting quotes - I’ve heard back so far from Nu-Heat for their LowPro Max. I’m concerned with appropriateness for the existing building, cost, additional lost ceiling depth (although I’m pretty short!), and if there’s a building regs issue with presumably having no insulation with the original concrete floor. 

 

We’d like to do UFH in the 30m2 extension and have been quoted so far for Nu-Heat’s relevant system. 

 

The grant from April closes the financial gap between a heat pump and a new gas boiler, as if we went for old school gas there would be extra costs to replace the ancient combi as well as moving the gas supply (crazy money!), required to accommodate the new floor plan. So as there would be a relatively minor jump in cost to a heat pump, we’re wondering if the time is right now? And if so, how this would influence the choice of UFH vs rads in the existing part of the house?

 

Would really appreciate your ideas, observations and experience. 

 

Big thanks

[ProDave]

Re UFH in the original house.  You have limited headroom and you NEED at least 100mm of insulation under the UFH so your only option is dig up the present uninsulated concrete slab, dig down further and re lay with proper insulation under it.

[PeterW]

9 minutes ago, Greatescape said:

The existing property is 60m2 with a concrete floor

So there will be no insulation under it as you say,  no way it will be suitable for UFH so discount it now unless you’re taking up the floor. 

 

10 minutes ago, Greatescape said:

We’d like to do UFH in the 30m2 extension and have been quoted so far for Nu-Heat’s relevant system. 

That is ok - assuming you want supply only you can get this at half the price or less that Nu-Heat have quoted you. 
 

11 minutes ago, Greatescape said:

The grant from April closes the financial gap between a heat pump and a new gas boiler

What about everything else you need ..?? ASHP will need a hot water tank (unvented cylinder etc) as a gas combo doesn’t. It could be substantially more than you think. 
 

12 minutes ago, Greatescape said:

Even if we couldn’t afford a heat pump now, we’d want to make it as ‘heat pump ready’ for the future as possible by using low flow temp rads, etc.

Make the rads 25% larger as the new ASHP flow temps are getting higher. 
 

14 minutes ago, Greatescape said:

pipework chased through the walls,

I doubt there is much by way of cavity wall insulation so why not line all the external walls with insulation or insulated plasterboard and you can bury the pipe runs in this - you will need to sort insulation overall as these houses were not built to be warm ..!

 

 

[JohnMo]

If you want UFH you need a well insulated slab.  A U value of about 0.15 or better would be your target. That would require a minimum of 150mm PIR.  Without that you will be pushing too much heat downwards and it will be expense to run.

 

To make running costs of an ASHP viable, the house needs to be well insulated.  An ASHP will convert 1 unit of electricity to 3 of heat, but that unit of electricity cost 5 times that of gas.

 

I would do the following

Insulation aim for u values of 0.15 or better everywhere.

Airtightness

Electric or dual water/ electric towel rails, in bathrooms to allow towel drying in summer.

Possibly electric UFH in bathrooms, so it is quick to respond and you heat only when needed.

Revisit gas move costs, do you need to move meter or just reroute pipes?

Look in to MEV with heat pump (link below) or similar.  This may have advantages if your house is not airtight.  The balance of the heating with IR Radiators, or A2A heat pump.

 

https://kers.co.uk/kers-mev-landing

 

[Gone West]

47 minutes ago, Greatescape said:

the very fashionable original self-adhesive tiles are below an equally fashionable retro carpet

I would check the tiles for Chrysotile Asbestos as it is a possibility.

 

49 minutes ago, Greatescape said:

Nu-Heat for their LowPro Max

This system outputs more heat per m2 but without a well insulated slab you might be losing half of the heat downwards into the ground.

 

52 minutes ago, Greatescape said:

if we went for rads here it would be a big job including all the pipework chased through the walls, etc

 

If you used IWI the pipework could be hidden behind the plasterboard because you will need some form of wall insulation.

[Iceverge]

I think you should price up a bulldozer renovation. You might be surprised at how little difference there is vs a complete remodel for a vastly superior end product.  

[Bruno]

No matter which option you choose, you should note that any heating system will only need to restore the energy lost. You should really take insulation serious. That's why @Iceverge's answer does make some sense.

 

Still regarding heating options, why not AC?

Edited January 25, 2022 by Bruno

[gmarshall]

There is no reason you couldn't put UFH in your new extension (with a properly insulated slab) and treat the old bungalow separately. Lots of us have UFH downstairs and rads upstairs. Regardless though, comparing uninsulated concrete floors in our old house and our insulated ones in our current refurb (we went the dig down and insulate route- it's not as bad as it sounds!) the difference in comfort alone is startling before you even get into heating costs. 

[epsilonGreedy]

@GreatescapeI think you need to re-appraise what is achievable in this renovation given your starting point.

 

A ceiling height of under 2.25m throughout the property will feel oppressive and could undermine final market value, so that rules out UFH unless you commit to digging out the concrete slab but that will raise your renovation cost to the point where a knockdown and rebuild could make more sense.

 

By the end of next week we will be looking at a kWh price of around £0.30 and at this price point ASHPs only make sense for the highest spec Passiv houses that can be heated overnight at an Economy 7 rate. Such homes can retain enough heat during the day and top up with more kWh the following night. Your renovated home will be way way short of this performance criteria. With that floor you will struggle to better an EPC band C score.

 

Let's review what you can do:

1. If a solid concrete floor then the current U value will be too horrible to calculate and even worse in a bungalow it represents a higher proportion of your external surface area.
2. Loft space, yup a U value between 0.11 and 0.15 is realistic providing the roof pitch is not lower than 30 degrees.
3. Walls. Probably around a U of 0.30 currently. Lining with 52mm thick PIR backed plaster board will get you down to 0.20 but that will be quite expensive and in a smallish 60 m2 foot print you will loose 2" to 4" off some room dimensions.
4. Windows: Given floor heat loss and likely final market value of the finished project it is not worth going mad here and putting in 3G Passiv house type glazing.

My advice is new gas heating, UFH in the extension only and maybe MVHR if your air leakage score is below 3.

 

In your position I would go back to the architect and say you accept the thermal performance of the main building will always be so-so. So you want to zone the property and create a thermally high spec 45 m2 of daytime living spec, insulate the heck out of the 15 m2 contributed from the original building to create this space. I am imagining a kitchen/snug with 75mm of PIR under a wooden floor and 2.2m ceiling height, then stepping out into an open plan 30 m2 extension with UFH and 2.5m ceilings.

[ReedRichards]

I know next to nothing about them but it seems you can now buy "Low Temperature" gas boilers which operate in the same sort of temperature regime as a heat pump, particularly a heat pump serving radiators and are more efficient than a conventional gas boiler.  So you might want to consider getting one of these with suitably sized radiators and benefit from the current lower running cost of gas heating but having  something that is more "heat pump ready" when you need to replace this gas boiler and gas boilers are no longer sold. 

[Andehh]

5 hours ago, Iceverge said:

I think you should price up a bulldozer renovation. You might be surprised at how little difference there is vs a complete remodel for a vastly superior end product.  

 

This is exactly what we did, cost around 8% more (as you don't pay 20% VAT)...but you get a brand new home!

[Iceverge]

Realistically I think it's cheaper. 8% in time and money isn't long disappearing into an old building with all the sins of the past that are lightly to be unearthed! 

[ProDave]

5 hours ago, epsilonGreedy said:

By the end of next week we will be looking at a kWh price of around £0.30 and at this price point ASHPs only make sense for the highest spec Passiv houses

It remains to be seen what is going happen to energy prices.  While many are indeed predicting electricity at 30p per kWh, a 50% increase on what I thought was already a stupid high price, the same people are predicting gas may go up 100%

 

We have no control over this, but you DO have control over the house you build and it is becoming more and more important to get at least close to passive house standards when you have the chance at a major renovation or rebuild.