Hello
Im new to the forum and although Ive read a lot I’m still confused as to the best option for the heating and dhw. Most installers seem to only want to do what they want to do rather than provide advice as to options and pro’s/cons!

I live in a little 55sqm single storey cottage in Sussex with no mains gas. Installed is a 210l DPS heatbank fuelled by a Charnwood 16B stove (8.6KW to water) burning wood with 3/6KW immersion for back up and a solar coil although I didn’t have the panels fitted as I quickly decided to plan an extension. Works ok but tank is small if the stove is on all evening. Walls are single skin brick but insulated with 100mm sheeps wool and loft insulated with 250mm sheeps wool.
The new extension is planned to include demolishing 15sqm of the existing and building on the side then 1.5 storey (about 50sqm each floor) with 2 bedrooms and shower room upstairs and hall, utility and kitchen diner downstairs – all insulated as per current regs and with ufh on new ground floor (about 50sqm) and rads upstairs and in existing building. Existing part will have ewi and new dg windows as well as small infill on one end to add another bathroom. Have room for a wood stove in the existing sitting room and also in kitchen diner
There isn’t room to add large pellet store and narrow access makes delivery of blown pellets difficult. not much room for a chunky pellet or log boiler. Could store logs in various places on the plot.

Does anybody know anything/have thoughts on the walltherm zebru? Seems like a lot of work to operate but maybe I am wrong. Or the klover diva to have in the kitchen either of which feeding a 750 or 1000l akvatherm solar tank?

Ashp with solar thermal for summer dhw-keeping the stoves for room heating?
Can the ashp generate water hot enough for baths/showers?
what about keeping the current heatbank and using it with ashp for the ufh heating only and a separate tank for dhw fueled by the solar thermal in the summer and the back boiler in the winter? In this arrangement could the ashp be "switched" to the dhw tank in the summer to top up the solar or is solar alone enough?

At this stage the design is not fixed so I'd like to get the right combination and really dont feel confident that I know how to do it– any thoughts?

as you can see I am def "confused" from Sussex

Hi Peter
Thanks for responding. The 210l is just enough for 2 showers in the morning so I am worried that there will not be enough hot water when the house is bigger. It could well be that it is not set up correctly as the top seems to heat well and then overheat but 2 (quick) showers and the water is cool. Also even if it is reading 75 + at night, by the morning the temperature has usually fallen to 40. The gauge is in the middle of the tank- perhaps another temp gauge at the bottom would give me more info. The wood burner seems to feed into the middle of the tank. The tank has sprayed on insulation so perhaps it could do with more insulation? It doesn't have a laddomat fitted - perhaps that would help get it up to temp faster?
Any ideas how to get the bottom of the tank hotter?

For the space heating I would be afraid to only rely only on insulation. In the existing part that would remain I can increase the ewi but again it is pretty cold now unless I have the stove going most of the evening and the rads on and does not retain the heat once the rads are off but would of course be better when the ewi done but even so not sure I can get it to the point where it doesn't need any heating.
You don't think ufh is worth the expense?
The roof direction is not the best for pv - mainly east/west with a small section of south but some shadow potentially from a fir tree.

Let's look at your DHW.
You say you have a cylinder that holds 210 lt, can be at 75°C at the top, but can cool to 40°C at night.
Heat is leaking out somewhere.
Is all the pipework insulated?
How much insulation is on the cylinder?
What is the flow rate of the shower?
How long is a 'quick' shower, 3 minutes, 15 minutes?

An ASHP is ok to preheat the water to about 35°C, but after that you are dropping the CoP to close to 1 during the winter, so consider resistance heating running on E7. It is cheap to install, very reliable, does what it says, and once efficiency is taken into account, about the same price to run as mains gas.

Now your existing house.
At 55m^2, it is similar in size to mine, though I suspect that your area exposed to the outside is greater (mine is a terrace and has an upstairs). My heat load is less than 1 kW, this can easily be supplied by a small Air to Air Heat Pump. You can get these from about £300, but would suggest a better one (Panasonic make some nice ones).

As mentioned above, get the insulation levels up, and improve the airthighness, and you won't need much heating.
PV has the advantage that it can be used for a lot of different things, ST is only for DHW, and needs maintenance. Not cost effective at all.

Posted By: plw666For the space heating I would be afraid to only rely only on insulation.

Can you expand on that? Do you not think insulation works?

Fabric-first on a retrofit is expensive, more expensive than speccing new technology. But it's the best way from minimising complexity, and giving you a healthy, comfortable house, and using less energy in the process.

Whether immersion or stove, I still think that there is a chance that you are not heating the whole tank, rather than that heat is being lost. You say that the stove feeds in at the middle of the tank - where does the return connect?

I agree with you Mike- I dont think the tank is being completely heated.
the feed is maybe a bit more than a third down the tank and the return is about 25% up the tank.

plw666 don't get carried away with which type of boiler to have or to have rads or ufh. First thing to do is to do some calculations about what you will actually need. If you look here
http://www.vesma.com/tutorial/uvalue01/uvalue01.htm
you will find a simple calculator for 'u' values for various construction types. Get your existing house and proposed extension, new window values, roof etc. and do a count up of the heat losses with various thickness's of insulation. Once you have this start thinking about how to satisfy this demand

For construction methods I much prefer solid wall (some sort of block) and EWI. Simpler and cheaper than cavity wall and none of the risks of timber frame. (A good target for the wall is a u value of 0.16 or less, a 250mm block and 250mm of EWI will give a u value of 0.13 or less depending on the block).

Posted By: plw666For the space heating I would be afraid to only rely only on insulation. In the existing part that would remain I can increase the ewi but again it is pretty cold now unless I have the stove going most of the evening and the rads on and does not retain the heat once the rads are off but would of course be better when the ewi done but even so not sure I can get it to the point where it doesn't need any heating.

There are several on this site who don't need heating, tony being the most famous! As I said above either an electric fan heater or an oil filled electric rad can be enough - or a couple of rads off your wood stove, directly and not via the tank would do. There are also those here with well insulated houses who have problems finding a wood stove SMALL enough to meet the needs. (sub 5kW is difficult to find!)
Do the calculations with the above link to see what your current demand is. At least as important as thermal efficiency of the fabric is air tightness, sometimes more so. If the place leaks like a sieve then you will never get it / keep it warm. Don't confuse what you have now with what you could / should have after the building works. It's like going shopping when you are hungry - you always buy too much!

Posted By: plw666Agree that insulation will need improving and as Peter said I have to add as much as i can but there are limits to what can be added without compromising on space. The property is detached so exposed all round.

If you can EWI then space is not usually an issue.

Posted By: plw666You don't think ufh is worth the expense?

Nothing wrong with uhf but if the house is well enough insulated (including the new floors and the old ones if possible) then its not needed and a small rad or two will be enough and much cheaper.

Your current heating system obviously has problems. Your original post did not mention rads, are these connected to the 210l tank? if so how and where. How is the system run, fully pumped or some gravity (e.g. stove to tank)? And a diagram would help.

Posted By: Peter_in_HungaryThere are several on this site who don't need heating, tony being the most famous! As I said above either an electric fan heater or an oil filled electric rad can be enough - or a couple of rads off your wood stove

A major difficulty for people believing in zero heating is the lack of evidence. There needs to be some quantitative evidence certified by third parties because it's all too easy for people to be misled or mislead themselves and others, whether intentional or not. What was the design? How was it modelled? Who did the modelling and what reason is there to suppose that they got it right? What is the reality - both for the total energy consumed and for the temperatures achieved and for the external environment? And so forth?

The other difficulty is that set out most clearly by Alan Clarke - namely that if you commit to a strategy and then discover that you can't meet the requirements, you're stuffed. Now to some extent it is possible to escape that trap by the plan B of using fan heaters etc but there are limits to that.

And then you have the huge extra complexity in the design space imposed by cost and in a lot of cases by ecological desires. As Dick Strawbridge famously said, it's not easy being green.

Posted By: plw666problem will be price as its pretty expensive per sheet but thin. 250mm of something else is prob cheaper but much thicker.

I think what you haven't yet explained is why extra thickness would be a problem?

Posted By: gravelldPersonally I'd love a house than could be heated by a fan heater or two!

You can buy mine, I shall add an extra £50,000 to the price.

I am with djh to a certain extent. Two reasons I get away with it is that I am in the SW and put up with cold rooms (I basically just heat the room I am in)

hahaha millionaire I am not but the ewi is for the existing building so not too many sq metres. something cheaper but thicker will mean back to planning committee as its in the national park.

diagram is in progress and coming soon.

while the tank heating needs to be sorted I'm still wondering if 210l tank for dhw is enough for house planned to house 3-4 people showering in the morning.

In the national park footprint and design is controlled. It should be ok but just means a re-submission.

Fair point. Nothing quantitative (some of the more enthusiastic home owners often have charts to show you but I know you meant something third party and credible).

Posted By: DarylPWe have approx 1 year data, int. and ext. temps on an XLS that show a house, designed and built well, with a family of 4 (2 adults, 2 children), needed only a couple of fan heaters for heating.
The int. temps were quite stable despite fluctuations in ext. temps over the year, so we are confident the design was shown to work.

You're doing better than me! Apart from only having been in for about 8 months, I don't have any logging yet, apart from temperature and humidity within the walls. I do know the temperature has been above 20 °C the whole time because that's how I decide when to turn the hairdryer on (actually a post-heater in the MVHR ducting). But I haven't recorded when I switched the heater on. I do have electricity bills and am starting to take monthly readings. My wife faithfully records how much solar energy the PV panels generated each day and how much was diverted into the thermal store. But I don't know what the immersion added to that. And we have worked out that two of us sitting in the living room with the TV on is enough to keep that warm at the temperatures we've seen so far this year. And our PHPP is being audited at the moment.

So we're quite happy but I don't think I have convincing evidence to show why.