180 litre isn't going to do much of any of the things you've listed, let alone all of them. 180 litre is not even that big for a simple hot water cylinder.

Not sure about GHG, but the RHI scheme is void if any solar goes to heating, must be a stand alone DHW only - check that angle out.

Is solar PV an option for you, in lieu of solar thermal?

I fitted a Gledhill because it came with heat exchanger for DHW and lots of ports for solar, boiler, wood boiler etc. Cant fault it, but your biggest challenge is the controls. I hacked a Nest and have CH controlled by the thermostat and programming online, and the gas boiler using the dhw facility to program online.

Useful info thanks. I am going with solar thermal as solar panels are not offered under the Green Homes Grant. Not sure why. I'm not too worried about RHI payments as they are low for solar thermal hence I don't mind forgoing it to use the solar thermal energy for the UFH. Although arguably this will only work best in the summer when the space heating demand will be lowest. But still. I am sure I will be heating the house most of the year. A gas boiler will also feed in. The house is not huge, a 2-bed converted into a 3-bed with kitchen extension. What sort of size should I be looking at?

The controls are sounding tricky.

I concur with Philedge, the Resol control system is brilliant with solar thermal. Mine can be programmed to divert flow from the DHW tank when that is satisfied down to my thermal store acting as a heat dump during the summer.

Can I ask why not ST for the UFH?

Posted By: modernvictorianCan I ask why not ST for the UFH?

Because neither ST nor PV will provide significant energy during the heating season. What there is won't even supply all the DHW, so it's a waste of effort and resources to design a system to do both.

A heating buffer is one thing, trying to make it do double duty as a source of DHW as well is fraught with problems, as the many threads on here demonstrate. The water in the UFH system already provides some buffering.

MV, if you're plan is to have a thermal store, which will provide DHW and also UFH, then I see no reason NOT to connect ST to it. You'll get a good contribution to you your DHW, and at other times some contribution to UFH. Indeed, since UFH will return quite cool to the base of your TS, it will provide a good low temp zone for your ST to feed into.

Whether you should have 2 cylinders (one for DHW and a buffer) or one larger TS is another debate. I've done dozens of TS's often with ST input. Given a choice between ST and PV, I'd input PV to a TS, as it's more flexible, but again there are various tunes to play on that.

True there are some difficult stories on here, but the initial design clearly wasn't right, rather than the principle not being sound.

For me the worst case scenarios are ST feeding too small a cylinder, or having a design where by the bottom (at least) of the cylinder is always hot due to another heat source, so no chance for the ST to contribute.

Some basic understanding of how much DHW you plan to use, what size of ST panel you are able to fit (afford) - which is the horse, and which the cart is for you to determine - and then you can size the cylinder.

Gas boilers are less sensitive to short cycling than just about any other heat source (direct electric apart). If you have a very well insulated but low thermal mass house, then short cycling may be much more apparent, due to low and frequent calls from the room stats. That said, storing energy from a gas boiler as hot water doesn't make sense, better to store energy as gas.

There's possibly an answer in there somewhere???

Thanks. I fear I am running out of time to make a well informed decision on this. I am meeting with the plumber on Thursday to finalise the design! It is one of things I kept getting out and putting away again as there doesn't seem to be any best solution.

I have just received a quote for an Ecocat. It seems expensive but it is two separate tanks so may solve some of the problems with trying to achieve too much with one tank. But I am now wondering if a TS is the right way to go.

I have to go with solar thermal not PV and can only realistically fit one panel (hard to estimate the area but around 3 - 4 m2 at a guess).

The DWH demand has not been calculated but it is certainly not huge. Two person household. So one shower and one bath per day max. Dishwasher does the washing up :-)

I have taken heed of the advice here and decided not to go with any sort of system which tries to mix DHW and heating from the same tank. So options are either the Chelmer ecocat which is two separate tanks in the same box, or an unvented cylinder with solar coil (maybe with an UFH buffer to stop the gas boiler short cycling but conflicting advice on this).

I spoke with Chelmer by phone today and they can install a solar coil in the heating buffer tank so that is an interesting option. But you would lose the RHI payments of course.

Just checked the RHI payments and yes they are more than I expected. I need to work out if the system I have been quoted for is eligible in its own right or if it needs an MCS installer and not just my plumber. As it stands the RHI would cover the cost over 7 years.

Maybe I could hold off on the coil in the buffer tank for seven years and then retrofit?! Or install but not use for 7 years. The mind boggles.

As a possible alternative I could install using the GHG and maybe there isn't the issue with using it for heating. I have finally found an MCS installer who has replied to me so hopefully I can get to speak with them to discuss.

You can use both RHI and GHG but the value of the GHG is subtracted from the RHI. But the same issue with heating. I need to look at the numbers. They don't make this easy do they.

<blockquote><cite>Posted By: modernvictorian</cite><blockquote><cite>Posted By: bxman</cite>Hi Jane

Sadly most of these government schemes benefit the trade and the administrators of them rather more than they do the environment</blockquote>

Having just had a quote back from on MCS installer it seems this is correct. The cost is basically the upfront cost from a non-MCS plus the value of the GHG. Really what is the point.</blockquote>

Exactly which is part of the reason I did mine myself plus the added bonus of learning something new doing a better quality job and having knowledge to fix thing later if anything goes wrong. Downside it takes longer and one is on a fairly steep learning curve but if you are that way inclined is very enjoyable and satisfying. Then we are all different and we all have different skill sets so DIY building will nor suit everyone.

Posted By: modernvictorianHaving just had a quote back from on MCS installer it seems this is correct. The cost is basically the upfront cost from a non-MCS plus the value of the GHG. Really what is the point.

Posted By: Ed DaviesOne of the many bad things about this is that it gives people the impression that heat pumps, etc, are intrinsically expensive when there's no real reason that an ASHP should cost more than, say, an oil tank and boiler.

In my experience when the government sticks its fingers into the market place with grants and subsidies things get skewed (screwed??) It happened here when the gov. gave big grants to families to buy and build houses - guess what happened - property prices, building materials and the cost of building all went up to meet the grants.

Oh and the EU common agricultural policy has been skewing the price of food for years to the point that the shop price bears no relation to production costs.

Posted By: djhPS I don't understand the fashion for planting trees. AIUI when a place is left to go wild trees (native trees) just grow so why is there all the fuss about buying and planting them?

Because, as you say, nature left to its own will finish up with a forest (probably oaks in the south of England!) however this takes time going through a shrub stage first.
This is not what is wanted.
People want orderly trees of the type in fashion at the time in a managed fashion. Also lots of trees are planted with financial support (grants or subsidies) and letting nature taking its course would not align with the paperwork accompanying any support. Basically management is needed and leaving things alone is unacceptable to the bureaucrats

Posted By: bxmanAs I recall this time last year the politicians promised that a vast number trees were to be established to counteract our Co2 emissions .

Is anyone able to verify this promise has been kept?

Not to the extent expected: https://www.woodlandtrust.org.uk/press-centre/2020/06/government-planting-figures/