Wood pellets or oil, ufh or rads

[RedLeicester]

Renovation said:

I understand that it runs at lower temps but if it's on (effectively) permanently against my rads which are on for half an hour in the morning and 5hrs at night I cannot see how it can be cheaper to run.

Assuming the same size / insulated house and heat escapes at the same rate the greater the heat differential between inside / outside the more heat escapes - so my house is the same heat as yours for 5.5hrs - albeit losing more heat near the rads but yours is losing heat for 18.5 hours a day more than mine - I cannot see how that can work out cheaper.

(I'm about to spec my extension floor so want to ensure I'm not missing something)

It's all about the slab.

It takes x amount of energy to heat water to 40 degrees, it takes a whole lot more to heat it to 75 degrees. So there's one "economy".

When that water is pumped through radiators they get hot, then the heat is lost into the room and it's gone. When it's pumped through UFH in a slab it heats the slab up which then slowly releases the heat during the day. Yes it is always "on", but that doesn't mean it's always being actively heated. In essence the slab acts as a massive battery, slowly releasing its energy over time and being topped up little by little, instead of one massive explosion of heat which is then lost.

For the sake of example if I go and turn the UFH off now, the floors will remain warm to the touch for another 18 or so hours, the rooms warm for 24 or so. By keeping it "on" all the time you're simply topping it up with tiny amounts to maintain that heat level, rather than running flat out. To heat the slab up from cold takes quite a bit of time and energy to be sure, but once it's up to temperature, keeping it there requires comparatively little. To be fair it took us ages to get our heads around the idea of "heating" being "on 24/7" as opposed to timeclock defined periods we were used to, so I can understand the confusion.

To put it in terms of heat usage, mine is run off the 3000l accumulator (again, think of a giant battery) attached to my log boiler. To run the UFH all day, that 3000l drops about 3-4 degrees in the space of 24hrs. If the upstairs rads kick in, it drops a further 12... So for the same amount of stored energy (or supplied energy from a normal boiler) I could run the UFH for 3 times as long as the radiators.

To look at it another way - why do eco-houses spec UFH instead of radiators...?

Edited by RedLeicester on Wednesday 29th October 11:16

[CK11]

RedLeicester said:

UFH is way cheaper than rads to run, all the more so with renewables, dunno where she got that idea from. In order to run rads you need hot water up to around 70 degrees to make them hot enough to exude useful heat. For UFH that drops to 35-40. UFH is more expensive to install, but cheaper to run, vice versa for rads. We've put UFH throughout downstairs and left the rads upstairs for phase two. As it is I wish we'd just done the lot as the punch in the logwallet when the rads kick in is painful.

Warm up time depends on how cold the slab is and how big it is. Screed thickness depends on type of UFH used and how it's installed.

Ours is all zoned and controlled using Heatmiser thermostats - it "learns" the warm up time for the room so drops a few degrees off overnight and then kicks in in time to be up to temp at your desired time. Ours isn't on 24/7 so much as 365 - it's just constantly ready to go as and when thermostats demand.

Heatmiser is what we have been quoted for also, each room its own thermostat etc
Surprised to hear you say you wish you had UFH in the bedrooms, 90% of people seem to say Rads are better and more controllable for sleeping temps. Sand/cement screed seems to in the 70mm region, wet you can go down to 40mm btu a lot more expensive and problems then with tiling etc

I guess its the old argument that when someone thinks the heating is on 24/7, when its really not, its going to be a lot more expensive than switching the heating on for a couple of hours here and there in the morning and evening. I guess it also depends on how airtight the house is, how well it holds the heat if your out say 9-5. A lot of peoples thinking is what is the point in having heat running when no one is home.

[RedLeicester]

CK11 said:

I guess its the old argument that when someone thinks the heating is on 24/7, when its really not, its going to be a lot more expensive than switching the heating on for a couple of hours here and there in the morning and evening. I guess it also depends on how airtight the house is, how well it holds the heat if your out say 9-5. A lot of peoples thinking is what is the point in having heat running when no one is home.

Which is where the likes of Heatmiser come into their own - you can program it to be warmer when you get up, set back during the day, warm when you get home. Because so much of that is "stored" energy, all your heatsource will be doing is topping up.

[FlipFlopGriff]

Never looked at UFH but doesn't it depend upon the thermal property of the slab, what it is made of and the depth.
Can't reconcile in my head how it would be cheaper to heat the ground rather than the air.
Also from a maintenance perspective I'd not wanting to be digging the floor up every 10-15 years.
FFG

[Sleepers]

As above our heating/thermostat in on 24/7 365 days a year as it is controlled by temperature. Being an ASHP in a detached 100+ year old house in rural Scotland it is connected to Dimplex SmartRad Fancoils with UFH in the bathroom. Coupled with solar PV our total electric consumption is £900ish with a PV return of £1500pa for 25 years and RHI of £825.60pa for 7 years

[Tuna]

Ours is a wet 50mm screed, seems to behave well with our tiles. We have UFH downstairs and nothing at all (other than towel rads) upstairs. The UFH is on a timer in the changeover months as it only needs an hour kick in the morning just to take the chill off the floor. Then during the winter we just leave it on.

If you have a house that cools very rapidly (i.e. drops to near outside in 8 hours) then turning rads off will be cheaper. Otherwise, leaving heating on is not going to cost you more regardless of which system you have. If you have a system going on and off, the quality of the heat might suffer though - to pull the temperature up to 'comfortable', you end up having very hot rads which tend to cause draughts and hot and cold spots in rooms. Some people get confused between electric and wet UFH - electric systems are hugely more expensive to run (three times the cost of gas-based wet UFH, nine times the cost of logs).

[RedLeicester]

FlipFlopGriff said:

Never looked at UFH but doesn't it depend upon the thermal property of the slab, what it is made of and the depth.
Can't reconcile in my head how it would be cheaper to heat the ground rather than the air.
Also from a maintenance perspective I'd not wanting to be digging the floor up every 10-15 years.
FFG

Totally depends on getting the slab right, yes. No problems with tiling either, dunno where that came from, ours is tiled throughout, and tiles simply add to the thermal mass.

The way our plumber explained it was thinking in terms not of overall heat output, as ultimately both systems are the same, but to think back to old cast iron school radiators - they were so solid they retained heat for ages even after the heating was switched off. That's what the slab does - retains that heat and releases it constantly rather than a one-hit period followed by cold.

[Tuna]

FlipFlopGriff said:

Never looked at UFH but doesn't it depend upon the thermal property of the slab, what it is made of and the depth.
Can't reconcile in my head how it would be cheaper to heat the ground rather than the air.
Also from a maintenance perspective I'd not wanting to be digging the floor up every 10-15 years.
FFG

Air is (on the whole) a rubbish way to deliver heat - its specific heat capacity is so low you have to shift a lot of air to heat something. With a rad on a wall, the result is that you (usually) end up with a strong up-draught over the rad which effectively ends up heating the ceiling above you, then a strong down draught on the opposite wall and across the floor. As most people are physically closer to the floor than the ceiling, you're putting your heat in exactly the wrong place.

By contrast, UFH radiates evenly up from the floor across the whole room. You're not moving masses of air to do so, and you don't get draughts due to hot and cold spots. That means that you can heat less of the room and at a lower temperature for it still to feel comfortable.

Of course, you do have to plan your slab well - really good insulation under a thin screed - but I'd expect systems to need very little maintenance. There seem to be guarantees of 20-25 years out there and I don't see why the basic heat loop shouldn't last much longer.

[jason61c]

I've just had a green deal check done and a fresh epc.

The good news is that the space heat has gone up to 38000, water to 4000. so 42000. However 250mm of loft insulation takes 9000 off.

He did put the impact of wall insulation as -11000, I've done the goverment rhi calculator and it doesn't remove the solid wall value, so payments now start at £4k a year, not £2.7. Should I take this as god regarding payments? Should I worry about the -11000kwh for wall insulation?

[herewego]

Sleepers said:

As above our heating/thermostat in on 24/7 365 days a year as it is controlled by temperature. Being an ASHP in a detached 100+ year old house in rural Scotland it is connected to Dimplex SmartRad Fancoils with UFH in the bathroom. Coupled with solar PV our total electric consumption is £900ish with a PV return of £1500pa for 25 years and RHI of £825.60pa for 7 years

Why do you have it on when you're asleep?

[Sleepers]

herewego said:

Sleepers said:

As above our heating/thermostat in on 24/7 365 days a year as it is controlled by temperature. Being an ASHP in a detached 100+ year old house in rural Scotland it is connected to Dimplex SmartRad Fancoils with UFH in the bathroom. Coupled with solar PV our total electric consumption is £900ish with a PV return of £1500pa for 25 years and RHI of £825.60pa for 7 years

Why do you have it on when you're asleep?

The temp is set-back to 17c overnight. Only on the very coldest winter night, like winter 2010 will he heating come on.

Just like when the house is not occupied during the day when it is also set-back to 17c.

Cheers

Edited by Sleepers on Wednesday 29th October 18:45

[FlipFlopGriff]

RedLeicester said:

Totally depends on getting the slab right, yes. No problems with tiling either, dunno where that came from, ours is tiled throughout, and tiles simply add to the thermal mass.

The way our plumber explained it was thinking in terms not of overall heat output, as ultimately both systems are the same, but to think back to old cast iron school radiators - they were so solid they retained heat for ages even after the heating was switched off. That's what the slab does - retains that heat and releases it constantly rather than a one-hit period followed by cold.

My rads are cast iron school radiators which I've bought 2nd hand and refurbished.
Would have to have a lime slab and this would be covered with 9 inch square quarry tiles about 1-1.5 inches thick. May look at in our downstairs shower room which h will become a wet room eventually.
FFG

[FlipFlopGriff]

jason61c said:

I've just had a green deal check done and a fresh epc.

The good news is that the space heat has gone up to 38000, water to 4000. so 42000. However 250mm of loft insulation takes 9000 off.

He did put the impact of wall insulation as -11000, I've done the goverment rhi calculator and it doesn't remove the solid wall value, so payments now start at £4k a year, not £2.7. Should I take this as god regarding payments? Should I worry about the -11000kwh for wall insulation?

You'll have to do the loft insulation and get a revised green deal assessment, although you can do this easily yourself and TBH its a no brainer from a cost saving point of view anyway. You don't need to do the walls for the RHI payment but you may want to look at it as a cost saving, assuming you can and the impact on the room size. We're putting a timber frame up and filling with lambs wool insulation, covering that with wood wool board and then a final coat of either lime hemp plaster or just lime plaster. Finish with clay or other breathable paint. Can't do this on every external wall but doing it on some. Others will just be the plaster and paint finishes. The hemp lime can be put on up to 50mm in one coat, although it will take much longer to dry out.
FFG

[jason61c]

FlipFlopGriff said:

You'll have to do the loft insulation and get a revised green deal assessment, although you can do this easily yourself and TBH its a no brainer from a cost saving point of view anyway. You don't need to do the walls for the RHI payment but you may want to look at it as a cost saving, assuming you can and the impact on the room size. We're putting a timber frame up and filling with lambs wool insulation, covering that with wood wool board and then a final coat of either lime hemp plaster or just lime plaster. Finish with clay or other breathable paint. Can't do this on every external wall but doing it on some. Others will just be the plaster and paint finishes. The hemp lime can be put on up to 50mm in one coat, although it will take much longer to dry out.
FFG

Awesome, just had this confirmed too The best £150 I've spent. Ever!

I'm currently doing some walls in lime hemp at the minute, its good stuff but does take an age to dry. I do plan on putting something breathable on the inside like yourself on the exposed walls.

Just waiting on some people coming round to give fixed quotes, looking at Froling/Effecta/hoval/ETA. I'd like something that will outlast the 7 year RHI.

I'm quite excited

[RedLeicester]

FlipFlopGriff said:

RedLeicester said:

Totally depends on getting the slab right, yes. No problems with tiling either, dunno where that came from, ours is tiled throughout, and tiles simply add to the thermal mass.

The way our plumber explained it was thinking in terms not of overall heat output, as ultimately both systems are the same, but to think back to old cast iron school radiators - they were so solid they retained heat for ages even after the heating was switched off. That's what the slab does - retains that heat and releases it constantly rather than a one-hit period followed by cold.

My rads are cast iron school radiators which I've bought 2nd hand and refurbished.
Would have to have a lime slab and this would be covered with 9 inch square quarry tiles about 1-1.5 inches thick. May look at in our downstairs shower room which h will become a wet room eventually.
FFG

We had them in our last house (which was a converted school), found them from skip dipping at a local grammar school which was ripping them out. Bought 18 of them for about £100 IIRC!

[FlipFlopGriff]

jason61c said:

Awesome, just had this confirmed too The best £150 I've spent. Ever!

I'm currently doing some walls in lime hemp at the minute, its good stuff but does take an age to dry. I do plan on putting something breathable on the inside like yourself on the exposed walls.

Just waiting on some people coming round to give fixed quotes, looking at Froling/Effecta/hoval/ETA. I'd like something that will outlast the 7 year RHI.

I'm quite excited

My installer tried a tie up with Treco but he said they don't have the depth of backup which is why we eventually went with Windhager. Until Biomass picks up its all pretty new to everyone. Would defo recommend going with an established proven make, but do check and double check its on the RHI approved list and the same with the installer. Any small error and your RHI payments will be gone. I was only able to apply from 7th October hence its all fresh in my mind.
You'll need an occupancy assessment number as well as the EPC number (both 16 digits from memory)which you should get with the Green deal assessment.
FFG

[jason61c]

Yes, treco have started supplying the Effecta biomass boilers for that reason, as a move into the domestic market with a proven boiler, I've googled it till i'm blue in the face and it puts them in the top 4 with windhager/froling etc etc.

did you go for a buffer/accumulator tank also?

[Tuna]

FlipFlopGriff said:

Until Biomass picks up its all pretty new to everyone.

I have a feeling that micro-scale biomass is not going to pick up - it's going to remain a niche interest long term. I'm basing that on two reasons - firstly, biomass has been an emerging technology for well over ten years now and though systems are undoubtedly better, none of them are breakthrough better (there are only so many ways you can burn wood etc.); secondly running biomass at the household scale is inherently inefficient (either in terms of plant, labour or energy cost to run the system), so you need some dedication (or incentive) to do so. The government schemes help of course, but they don't make installation, maintenance and ownership any simpler so I doubt we're going to see a critical mass happen.

I could be wrong, but large scale and possibly district scale generation are more likely to become the big focus of biomass, and householders are going to be largely composed of people wanting to heat their quaintly rustic pile economically. That's not a big or growing user base.

[RedLeicester]

I don't get the "emerging" or "new" technology thing. Domestic Biomass log/pellet boilers have been around for 20-30 years, just not in this country, and farm log boilers have been around in this country for years too. It's a well established technology hence why things have moved from a bunch of logs in a cast iron shell to log gasification systems, lambda sensors, ceramic ignition, automatic ignition, self-cleaning, self-dousing, network connectivity, multi-zone and multi-thermostat systems and so on. Yes there are only so many ways you can burn wood, but there are a hell of a lot of efficiencies in the process and manner in which it is done. It's a bit like saying a gas boiler is just a gas boiler, yes and no. As I mentioned before, I nearly died laughing when the manufacturer of mine sent out an engineer to run a firmware update!

District / commercial systems are fairly widespread too (our local council built new offices a couple of years back which are all log chip fed, one boiler for multiple buildings) and again overseas it's common for entire housing estates to have centralised heating. In 2006, over 10% of Austria's heating was biomass, Lech ski resort is heated by biomass too and it's a similar story in Scandinavia, though ironically they actually import a lot of their wood. As always, the UK is late to the party. The grants/incentives certainly help and lessen the pain, but as my earlier calculations showed, even without them the savings are colossal in the right circumstances. There are certainly some new an interesting companies on the market, along with an awful lot of dross too. We narrowed ourselves down to the Finnish / Austrian makes who have been at this game for decades so have a long proven track record and seemed to know what they were about.

Jason - may be worth having a chat with Euroheat who are the UK importer for SHT and HDG, two of the big Teutonic brands.

[CK11]

4 Pages in and still non the wiser even though better informed!