I'm considering UFH for our Victorian ecoretrofit, for the first floor bathroom and the open plan kitchen/living room. The bathroom will be first, the downstairs will probably but not definitely happen. My priority is to cut carbon and use non-toxic materials - this means they should be natural, biodegradable or recyclable.

I'd like advice on the type of system and on the Carbon Question (below).

Systems:
I am looking at 3 options:
- wet UFH throughout, run on gas - advantage is that we could in the future swap this to running on an air source heat pump
- electric UFH in the bathroom (easier and cheaper as we're doing this room first) and then wet in the downstairs rooms if/when we get round to it
- a sort of hybrid - a system from Jupiter, which uses a tile instead of screed, so a wet system but dry install. Advantage here is the ability to specify wood fibre insulation instead of EPS (expanded polystyrene) and not totally bury the pipes that run underneath the bathroom floor under a solid screed.

The Carbon Question:
I've installed solar pv which should generate c. 3000kWh pa. We use c. 600kWh. Both figs are based on 6mnths data, Jan-July. (I now realise I overspeccd this and should have gone partly thermal. Bugger.)

So if I install electric UFH in the bathroom, do I make a carbon saving as compared to using gas, as we generate so much 'surplus' electricity? I haven't got any storage for the pv and obviously we'll be mostly using grid electricity when we actually need the UFH on, but is the net effect one of saving carbon? I buy electricity from Good Energy.

Stick up as much pv as you can fit and use export dump box for HW. Costs less and more useful than solar thermal

@alexj, if you are concerned with Carbon (CO2?) reduction, reduce grid electricity usage where ever possible.
If the use of oil-based insulants enables you to do this, it is worth it.... a Kwh saved is a kWh saved forever!

Posted By: alexjI've installed solar pv which should generate c. 3000kWh pa. We use c. 600kWh.

Have I understood that correctly? You use a total of 600 kWh a year? What does that cover? How much energy of other types do you use?

We have gas central heating (under 500 units, from memory around 1550kWh)

The analysis from the Centre for Alternative Technology is questionable as more PV is installed given that everyone will tend to be exporting at the same time in a local area. However the FIT payments should have been lower and the export payments higher.

(I think the CAT is clearly correct that heating water with gas and exporting from PV saves carbon, but that it will not save as much as they say over the next 20 years.)

Decc reported 2016 UK mean electric grid intensity is 0.41205 kgCO2e/ kWh and gas 0.20444kgCO2e/ kWh.

https://www.gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2016

This means UK electricity is becoming less carbon intensive than when CAT looked, but it's still much better to export all PV into the grid, and heat houses and hot water with gas. Interestingly, ASHP is now lower carbon than gas.

AIUI the purpose of diverting PV from grid into heat, is to play clever tricks with deemed export, which maximises tariff payments, at the expense of all other bill payers and of the environment.
:-p

You could consider that electric ufh system may be cheaper to purchase than a gas boiler, maybe the cash saved could be spent more effectively to save CO2 elsewhere on your project (or even on another community project?)

James, that's right, I oversimplified. As STs figure showed, even under optimistic conditions the grid intensity is worse than gas, and under worst case winter conditions it will be much worse. So whether in best/mean/worst conditions the answer is always best to export PV and heat with gas or ashp.
This should be done using marginal not overall intensity, for which I havent seen official figures, but plenty on blogs such as earth.org.UK

Edit: http://www.earth.org.uk/note-on-UK-grid-CO2-intensity-variations.html#fullyear2015

There's so much complexity around exporting electricity to grid and importing back to use, including ever changing spot prices for energy, also depending on geographical location. Richardelliot you're right on cost but for me it's more about the carbon on this one - I'll have to weigh up both but am not operating solely on financial payback. (Why is it that no-one talks about payback on a new laptop or car or sofa or ... insert other expensive product?!)

I think on balance I'm leaning towards a wet system powered by gas central heating for now and air source when I can afford it. Again if anyone has recommendations from personal experience on specific systems I'd appreciate it.

On insulation, for me a kilowatt saved is not the only measure of eco. I work with natural materials in housebuilding and believe in returning what we use to the earth at whatever point we deem the 'end' of its life. I don't think saving CO2 in the future justifies using toxic materials that harm people and planet all the way through their life and then at the end of it too, sometimes for thousands of years (e.g. pvc). Plus we have such great materials in the form of plant-based insulation (wood fibre, cork, hemp) which are local, pleasant to use, carbon-sequestering and high performing. Anyway, that's just to explain my position.

Posted By: alexjAgain if anyone has recommendations from personal experience on specific systems I'd appreciate it.

well this is just my five bob's worth...

Posted By: alexjI'm considering UFH for our Victorian ecoretrofit (...) My priority is to cut carbon and use non-toxic materials (...) I am looking at 3 options:

Would it be feasible to examine a 4th option, namely, LESS heating (or no heating at all ?) - good for carbon !

I am not being facetious - OK, your house is a lot older than mine (1983) but I have been investing a lot of effort in "killing" (read deinstalling...) our heating. Moved here 9 yrs ago, I immediately removed the 500-watt electric toaster (YUKK!) from our master bedroom, then a 1 kW oil-filled radiator from the kitchen, then a second 2 kW oil-filled ACOVA from the lounge, then the 2nd lounge (ACOVA) went downstairs into the lobby where it serves more use... in place of YET ANOTHER toaster that went straight to the dump...

All said installations (with zone-control robot to boot...) being (in my opinion...) superfluous to requirements since the house has (highly effective...) electric infloor heating...

My theory is that the previous owners were either EXTREMELY climate-sensitive (best assessment) OR they got ripped-off by the electric-board "wise-energy" initiative whereby they got 20% tax-free credit...). I fear that this less kindlier assessment is actually the better one...). Sorry but the rant has to continue...

Said "energy improvements" taking no consideration of the *enormous* *open* *fireplace*
or the need for extra insulation...

I started superinsulating our loft space, and we installed a wood stove (smallest model feasible...) and immediately stopped using the electric floors. Our electric bill is now less than one-half of previous owner's last bill. We don't feel cold. We have good solar gain and recently upgraded all our windows (at *some* expense...).

I now want to kill our electric DHW by installing solar thermal. I also want to try & use solar air for warming the basement - ongoing experiment but I intend to get there !

The point of my message is, insulate first, kill leaks, calculate and recalculate your heating requirement.
The good news is, the planet is getting warmer anyhow !

gg
Lat 48°N (FR channel coast)

Totally agree, the UFH would be to REPLACE rads and is in conjunction with killing all reasonable leaks (I've had an airtightness tests and there are easy, cheap wins, and I've done some thermal imaging too which has been revealing) and insulating. I'm putting in hempcrete internal wall insulation and cork or wood fibre externally where I can (conservation area). The aim is to reduce the heat demand. It is a Victorian house and designed to breathe so I'm not going fully airtight but will get down from 8 to 5 on airtightness. UFH appeals as a way to move totally off gas with an air source heat pump in the future.

I build with strawbales and worked on a passivhaus in straw that has no heating apart from MHVR, so totally down with that.

BTW I'm running a how-to-hempcrete workshop in Cambridge in Sept as part of Open Eco Homes - msg me if interested!

Gyrogear, if we had a 'like' button I would 'like' your post.

Tony, you're right but I meant that I'm not aiming for an airtight house! Happy to send the case study when done - is it for publication here?