New build heating system - Gas/ASHP, UFH/Radiators/Combination, MVHR?

[Nethermoor]

Hello all.

 

I am currently awaiting planning permission on a new build in Derbyshire, trying to make some decisions on my heating source and emitters, and how it works with MVHR.

 

I'm looking for a sensible, economical solution but will pay a bit more for a clear benefit.  I intend to move out of the house in 5-10 years so can't entertain anything with long payback periods.  Plans are attached to hopefully give context.  Intended build method is ICF, so the walls will have a u-value of 0.19.  Likely to have either block and beam (maybe Tetris), or a concrete slab ground floor.  Upstairs will be a suspended timber floor. 

 

Heating source - I'm guessing with gas (in the road but would need to make a connection) I'd be silly not to get a gas boiler?  Or would an ASHP still be a sensible option to investigate?

 

Heating emitters - With a solid floor, would UFH be an obvious choice for downstairs?  For upstairs I've looked at Omnie TorFloor and Pug Screed, otherwise just radiators?  Is forced air another option worth investigating?

 

MVHR - it would seem this is an obvious thing to have on a new build?  Should I look at an inline heat pump with this to provide some additional heating and cooling, or is this not really worth it? 

 

Be glad of any advice.  Thanks!

19-003-20-E Proposed Floor Plans-[A1].pdf 19-003-21-B_Proposed_Elevations-[A1].pdf 19-003-22-B Proposed Section A-A-[A1].pdf

[scottishjohn]

hi and welcome 

if you have mains gas its a no brainer- at first look --but ASHP woud give option ,with right unit to cool house as well

there will be no RHI worth thinking about with new build to near passiv specs -are you going to have solar pv+plan for battery storage when it gets cheaper?and maybe then run your ASHP on your own power ?

 

I would always say go UFH --so much more flexibility in where you put furniture etc with no radiators 

 

MVHR is a must with new air tight build --extra heating --doubt ti will be needed ,but could be retro fit later if you plan it now

depending on if its going to be open plan --you might not need upstairs heating --but you can still have wet ufh in a timber floor anyway - so maybe It would be a good choice to fit piping etc anyway-- your architect should be able to tell you that when heat calcs are done 

 sure you will get plenty of other suggestions --enough to make your head spin

 

[Conor]

I've looked in to this a lot as well... Come to the conclusion that a small monbloc ASHP with underfloor heating loops is the most cost effective (assuming gas price rises in near future) and lowest carbon emitting system. 

 

You should get your peak heating load figure from your SAP and go from there.

[SteamyTea]

Why only 0.19 W/m².K.

I thought walls had to be 0.16 W/m².K now.

Is that just the starting point or a typo.

[Alexphd1]

Dont forget a gas connection can be a few £k easily. Priority for me would be design a system that can easily be heated by either gas/ashp or direct electric. Nice roof for some PV!

[ragg987]

If you are getting PV, then you need to think of balancing the generated power against load so you are not exporting too much. This is where an ASHP is useful - a gas boiler is not much of a load.

 

In theory, for a low(ish) energy house, running cost of ASHP is similar to gas. If not a low energy build (which includes insulation, air-tightness and MVHR) then you may need to run the ASHP hotter so efficiency will reduce, and the equation might swing towards gas. And UFH makes more sense if ASHP as you can run it cooler and hence at higher efficiency.

 

A regular ASHP cannot heat water beyond 55C, so something to bear in mind. Also recovery time for the DHW is likely to be slower, so if you have a large number of occupants / lots of hot water demand you will need a larger water cylinder.

 

Finally think about gas for other uses - e.g. gas hob or oven. These are likely to be cheaper to run than electric appliances (though unless you cook loads the difference will be small), however can you live with full electric for cooking or must you have a gas hob? If you can live with full electric then this favours ASHP as you do not need the gas connection or pay the standing charge.

 

Sorry no clear recommendation, but I guess what I am saying is factor in your personal circumstances and also the WHOLE house and equipment should be seen as a system, you cannot make single decisions in isolation.

 

Other factors as others have already mentioned - cooling capability, connection costs etc.

 

In my low-energy build I have PV, UFH, ASHP, MVHR. I have previously always had gas / boiler / rads / unmanaged ventilation (i.e. opening windows!). If I were to build again I would not hesitate to repeat this combination, though of course the capital outlay is higher, but the increase in comfort is great and running costs as low.

[Nethermoor]

Thanks all for your replies.

 

Solar - all the calculators I've played with show a payback time of 20 years so I'd knocked it out?

MVHR - thanks for confirming this is a must.

Heating upstairs - ok, I will wait for some heat calcs

Wall u value - hmmm, I'd been assuming I was well within regs but will have to check with the architect on that one...

Good point on designing a system that is ready for ASHP even if I go with gas, I will bear this in mind with pipe spacing etc.

 

From what you are all saying I think I will cost up ASHP especially as I have the choice atm to make a gas connection or not.  

[SteamyTea]

28 minutes ago, Nethermoor said:

Solar - all the calculators I've played with show a payback time of 20 years so I'd knocked it out?

Is that because you got estimates for retrofitting, rather than fitting during the build?

[Nethermoor]

5 minutes ago, SteamyTea said:

Is that because you got estimates for retrofitting, rather than fitting during the build?

Possibly, just used generic calculators online.  Where would be a better place to get an estimate?

[SteamyTea]

4 minutes ago, Nethermoor said:

Where would be a better place to get an estimate

Scout around to find the best prices of either a complete kit, or individual parts, then ask your builder/plumber/electrician how much to fit.

There is scope to save on roofing, they don't have to be bolted on top on a frame, they can be integrated.

When I was working for a PV company, out two biggest expenses where sales commission and scaffolding.  You don't need one of them and the other you will have on site.

[ragg987]

49 minutes ago, Nethermoor said:

Solar - all the calculators I've played with show a payback time of 20 years so I'd knocked it out?

Apart from the assumptions around cost of fitting, the calculators will assume 50% is exported. Done right you can reduce export to nearly nothing. Our export in the 3 years has been 3%.

 

I calculate payback at 8 to 9 years, though I get FiT payments. I recently got a plug in hybrid electric car, this could improve payback but I have not done the sums.

[SteamyTea]

11 minutes ago, ragg987 said:

Our export in the 3 years has been 3%

I am paying for that.

Sorry, could not resist.

[ragg987]

3 minutes ago, SteamyTea said:

I am paying for that.

Thank you.

[SteamyTea]

1 minute ago, ragg987 said:

Thank you.

That's OK, going to be up your way next month, so shall come and take my share of it.

[Nethermoor]

1 hour ago, SteamyTea said:

Scout around to find the best prices of either a complete kit, or individual parts, then ask your builder/plumber/electrician how much to fit.

There is scope to save on roofing, they don't have to be bolted on top on a frame, they can be integrated.

When I was working for a PV company, out two biggest expenses where sales commission and scaffolding.  You don't need one of them and the other you will have on site.

OK, very interesting.  Could you give me a pointer where to start looking? 

Presumably it would be only worth putting on the south facing section of roof?

[ProDave]

1 hour ago, Nethermoor said:

Possibly, just used generic calculators online.  Where would be a better place to get an estimate?

If you are at all practical you can buy the parts for a 4KWp PV system for about £2K  I went a bit better and by a lot of careful shopping around got it down to £1500.  If I manage to self use £250 worth per year that is a 6 year pay back.

 

In this new non FIT era don't even think of finding a "solar PV company" to fit it  you should be looking at sourcing the kit as cheap as possible and self fitting or just getting an electrician to fit it.

[Jeremy Harris]

A couple of tips if you are thinking of a DIY PV install.  Firstly, have a read as to how @ProDave sourced his panels, mounts etc, as documented here:

 

 

Next, if you live in England or Wales, where Part P applies, then get an external cable run from the consumer unit to an external connection box, and have that tested as a part of the main electrical installation.  That way you can then do an entirely DIY installation without needing any additional sign off etc.  The additional cost when installing an electrical system for a single run of cable to an external connection point will be peanuts compared with the cost of getting a Part P person to come along later and connect things up.  Connecting an inverter to a terminal box is no harder than wiring a plug, just needs a modicum of common sense and care.  The same goes for wiring up the PV panels and connecting them to the inverter, it's not rocket science, and just needs the same care as making the AC connection, with the slight added complication that the panels cannot be turned off.  The easy way around this is to make off all the panels connectors without plugging any of them together (safe, as the voltage from each will be too low to be hazardous) and then wait until late evening to connect the panels up, or chuck covers over the panels to stop them generating whilst the connections are made.

[scottishjohn]

On 08/09/2019 at 16:46, SteamyTea said:

Is that because you got estimates for retrofitting, rather than fitting during the build?

also is that  that payback is making an assumption on electricity prices in 5-10 years time ,or just using todays 

if it keeps going at 10- 20 % or close to it a year then the calculation changes a lot

costs more i know but a 10kw array with batteries on modern house should see nearly zero grid usage except in winter

I know its hard one and as you say you will be selling house in 5years --then scrap some of what we have said and just go gas +ufh

 

[ProDave]

If the house is for short term, forget solar PV, it will never repay it's cost in the time, it won't add any value to the house, and it may even put some buyers off.

[Nethermoor]

Thanks again, I'm thinking the same on solar...if it was a 'forever home' it would be obvious but I can see I'll be struggling for payback in my scenario.

 

So UFH downstairs - but upstairs: I've had prices on the Omnie TorFloor and equivalents where the pipes are routed in chipboard and then have a structural ply over the top, and it seems quite expensive - around £5k for my first floor (after adding cost of 6mm ply on, and deducting what 22mm chipboard would have cost). There's also Pug screed which is cheaper but I guess the weight will cause extra structural costs, plus it looks a real hassle to install.

 

A couple of friends have said that I'll find the upstairs heating rarely comes on, and recommended just having an electric UFH for bathrooms and just some 'backup' heating in the bedrooms (radiators or electric heaters etc).  Be glad of anyone's experience on this? 

 

If I have to just bite the bullet that's fine, but I'd hate to spend £5k to find it only comes on in the very depths of winter!

[ragg987]

On 08/09/2019 at 21:57, Nethermoor said:

A couple of friends have said that I'll find the upstairs heating rarely comes on, and recommended just having an electric UFH for bathrooms and just some 'backup' heating in the bedrooms (radiators or electric heaters etc).  Be glad of anyone's experience on this?

We did not install UFH upstairs.

 

We have direct electric towel rails in bathrooms which are on 24x7 in winter at the lowest setting, maybe about 50W on average - about 2-3 months of the year. Rest of the time not needed (approx 6-7 months) or short bursts (2-3 months).

 

Our 4 upstairs bedrooms have direct electrical heating through the MVHR supplies (I think it is a 0.5kW heater - my memory is not so good) which I installed as a "just-in-case". I am glad I did it does need the heat when very cold outside, this has it's own thermostatic timer and I have it on a couple of hours in morning and same again early evening.

 

The cost of installing these devices is a few hundred pounds and running costs are low - maybe £50-70 per year. So much cheaper than a £5k install of UFH that you mention.

 

This is in the context of a passiv-standard build. Others have said they do not need heat upstairs. We like it quite warm - bedroom below 19 or 20C is too chilly for us apart from for sleeping.

 

On 08/09/2019 at 17:14, ragg987 said:

I calculate payback at 8 to 9 years, though I get FiT payments. I recently got a plug in hybrid electric car, this could improve payback but I have not done the sums.

Just done the sums given 12 months experience with the plug-in hybrid electric car. Simple payback of PV installation is reduced by approx 1 year, to between 7 and 8 years. [July 2018 to June 2019 : Generated 4,413 kWh of which I exported 1%, consumed 76% and diverted (to DHW) 23%]

[Nethermoor]

On 11/09/2019 at 21:27, ragg987 said:

We did not install UFH upstairs.

 

We have direct electric towel rails in bathrooms which are on 24x7 in winter at the lowest setting, maybe about 50W on average - about 2-3 months of the year. Rest of the time not needed (approx 6-7 months) or short bursts (2-3 months).

 

Our 4 upstairs bedrooms have direct electrical heating through the MVHR supplies (I think it is a 0.5kW heater - my memory is not so good) which I installed as a "just-in-case". I am glad I did it does need the heat when very cold outside, this has it's own thermostatic timer and I have it on a couple of hours in morning and same again early evening.

 

The cost of installing these devices is a few hundred pounds and running costs are low - maybe £50-70 per year. So much cheaper than a £5k install of UFH that you mention.

 

This is in the context of a passiv-standard build. Others have said they do not need heat upstairs. We like it quite warm - bedroom below 19 or 20C is too chilly for us apart from for sleeping.

 

Just done the sums given 12 months experience with the plug-in hybrid electric car. Simple payback of PV installation is reduced by approx 1 year, to between 7 and 8 years. [July 2018 to June 2019 : Generated 4,413 kWh of which I exported 1%, consumed 76% and diverted (to DHW) 23%]

 

Thanks, very interesting.

[eandg]

On 11/09/2019 at 21:27, ragg987 said:

We did not install UFH upstairs.

 

We have direct electric towel rails in bathrooms which are on 24x7 in winter at the lowest setting, maybe about 50W on average - about 2-3 months of the year. Rest of the time not needed (approx 6-7 months) or short bursts (2-3 months).

 

Our 4 upstairs bedrooms have direct electrical heating through the MVHR supplies (I think it is a 0.5kW heater - my memory is not so good) which I installed as a "just-in-case". I am glad I did it does need the heat when very cold outside, this has it's own thermostatic timer and I have it on a couple of hours in morning and same again early evening.

 

The cost of installing these devices is a few hundred pounds and running costs are low - maybe £50-70 per year. So much cheaper than a £5k install of UFH that you mention.

 

This is in the context of a passiv-standard build. Others have said they do not need heat upstairs. We like it quite warm - bedroom below 19 or 20C is too chilly for us apart from for sleeping.

 

Just done the sums given 12 months experience with the plug-in hybrid electric car. Simple payback of PV installation is reduced by approx 1 year, to between 7 and 8 years. [July 2018 to June 2019 : Generated 4,413 kWh of which I exported 1%, consumed 76% and diverted (to DHW) 23%]

Can you elaborate on what the direct electrical heating through the Mvhr supply is (and how it works) please? 

[ragg987]

It is a small electrical element that is connected in line with the MVHR flow duct. I have a thermostatic clock on the landing to control it.

 

As I did not want this to heat downstairs, only upstairs, I split the outlet from the MVHR into 2 runs and the heater is connected to the upstairs supply. I am using semi rigid piping to the ducts, it also meant I needed 2 manifolds.

 

MVHR > splitter > heater > manifold > ducts

 

https://www.bpcventilation.com/circular-electric-duct-pre-heater

[Oldsteel]

An interesting thread. I am in the prep stages for a new 200m2 two-storey build, and looking to design my own ASHP and UFH system as the renewable installers around here seem to be super busy and expensive. We have gas in the road but it will cost around 3k to get it in, so will be going all electric, and fossil fuels will only increase in price.  I had UFH downstairs and upstairs in my previous build, and needed it in the bathrooms 60% of the year and occasionally in the bedrooms when it got really cold. I am planning to do the same in the current project, but will have to gauge the installation cost. I wouldn't go for radiators upstairs due to the restrictions they introduce. As MVHR was the best thing I did in my last house  it's a no-brainer, but not heard before of the heating element. I just wonder though whether having heat blown down into the room - and then sucked out the other side through the extraction vent, is going to be either comfortable or efficient? I get that its low cost though.

Solar PV is also a must - as this is our forever house - but I have limited (south facing)  roof space - in a conservation area where they are picky about solar arrays. We have land at the back for a ground array, but its a slope facing north-west! There are however possibilities using the terrace to keep a south-facing array from view - if wife will allow?

Decisions decisions - that's what self build is all about!