JohnMo

So in effect tops up the TS via DHW side of the combi in the process I have written that incorrectly. Should have said boiler runs for about 10mins per hour. That is the central heating runs for about 10 mins per hour. The secondary return, will pick up heat from the store if it's available, the boiler will fire the DHW as required. I only run the secondary return for an hour in the morning and the same at night.

No its not a multi foil. That's the vapour control airtight layer. There is spray foam insulation inside the roof structure. Thermal losses not accessed, but at 40 degrees in the top half only isn't worth while assessing. The plastic cap on the top of cylinder is cool to touch. The water in the expansion tank, feels warm, but not hot. The room not much hotter than the rest of the house. The top of the room is being extracted to MVHR, so being recycled. The boiler came from Wolseley, it's an A325ECX, cost me £950 (including VAT,) including a standard flue. For one of the highest efficiency boiler you can get pretty good price. The main reason I chose it was it build out of the box to take solar preheated water.

I just heat the top half of the store, thermostat about half up store set to 45 degrees. I am using wood stove connection at top of store as my UFH take off

Just commissioned a system quite similar to you are talking about. Combi boiler - Atag can take pre heated water Thermal store, DHW Coil feeding into combi Combi central heating circuit, heating TS via sealed coil at bottom of TS. Water within store connected to UFH pump and let down to 30 degrees via mixer at manifold. Thermal store temp set at 45 degrees. Boiler central heating flow temp is a 50 degree curve. The only difference is my immersion is connected to PV diverter. So what you want I cannot do, but you can. UFH pump is running when a thermostat has a heat demand, boiler only runs when the thermal store asks for heat. Summer Turn thermostat down in summer so there is always a call for heat, but ensure the central heating demand is switched off in summer, so thermal store is cold. UFH heating will circulate back to store - no need to reverse. Heat at top of store will be consumed by cold water passing through upper coil prior to being heated for DHW. But you need the separation of UFH and boiler, but running through coils within the tank gives you this

Gone west, the floor is engineered oak, thát is finished in grey wax. Close image attached. Things I would have done different 1. The walls from strip foundations to DPC, are done in cement blocks, I would do them in durisol blocks - not reliant on someone else and would have had a easier transition to the main walls. 2. Had the roof structure designed around Pozi rafters from day one. 3. We have electric towel rails, would chosen them, before the electrical contractors arrived, as two sockets ended up in the wrong place. 4. Simplified the front wall as all the corners were a real pain to build as just every block has to be cut. 5. I would get the architect to detail door and window thresholds. As this was a steep learning curve. 6. I changed the build method to Durisol block part way through the warrant process, this gave us a 4 month delay. Things I wouldn't change 1. Shopping around for materials, local building merchants are super expensive. Contractors don't really care how much they pay, as they passing the cost to you, plus a percentage. Most contractors had the material free issued from me. 2. Planning well ahead, purchasing PV, Boiler, thermal store, MVHR, at start of first lockdown in clearance sales Things I learned The house ends bigger than you think. Things take longer to do than you think. Be flexible with material and design choices

The cold water enters the combi via the TS DHW coil. The recirculation pump is on the cold side of the coil. Check valves force the recirculation return flow though the DHW coil and to the combi. The pump is the bit with the shiny plastic top, next to the immersion. Have tried lots of running curves and the 50 degree one is about as low as I can go. The pump runs for about 10mins every hour or so. The combi basically runs until the return flow is just about the same as delivery flow.

Reminded me I need to complete one also. Found this - may be helpful https://www.gov.scot/publications/how-your-low-carbon-home-works/

I think ASHPs are good if you have a low energy home, but even then you at looking £10k install, (more with a high energy home) with grants you could half this. You will need bigger radiators as the temperature developed by heat pumps is lower than oil or gas. Heat pumps when optimised develop approx 3kW heat for each kW of electrical energy, but electricity cost 3 times that of gas, but not sure about oil. Oil boiler nearly produces a kW heat for each kW of energy put in. As everyone has said insulation is king, keep the heat in. Ventilation, part of your heat loss calcs is ventilation heat loss, an old house could have 10 or more uncontrolled air changes an hour, each of these air changes needs to be heated. An airtight house has 1, or less air changes per hour, that require heating. We have solar panels, but they only really produce lots of energy in the summer, if can get some gains in winter via an immersion heater that is good, but don't bank on it in a heating design. My recommendations are Find or build a spreadsheet, work out room heat loss as it is now, then modify spreadsheet with different options also look at costs. The more you move from what you have now, the more the cost, especially if you have someone else to do the work. In NE Scotland there is scheme running to apply external insulation, my wifes sister also in an ex council house has just had done for next to nothing, this included re rendering the external of the house. Insulation and fix drafts. Get a basic diagnostic air test done, this will highlight areas where you are leaking, to see if they expensive to fix or otherwise. There's a guy in Forres that does tests. Find out if you have a condensing oil boiler, if so optimise return temps from heating to a low 40 degree C, so it runs in condensing mode. This may require larger radiators to give the right output in to room, but much cheaper than biomass or ashp Look at your water cylinder check the insulation, my be worth keeping or replacing. Overall keep it simple

View from lounge window, still need decking to be completed

I have 10x Perlite all black 310w panels, GSE in roof trays, growatt inverter, from ITS Technologies. Around £2600 for everything, switches, meters etc except the optimisers, which I purchased separately. Installed myself got the electrical guys to wire as part of electrics install. No MSC cert, but planning to self consume (, immersion heater). Even today its producing 1.8kW, in NE Scotland, sunny but cloudy.

Could just be British weather, check a weather site, and look at local humidity levels, they vary day to day

No just strip foundations, but prity big

Hi update, house now built, just some cladding and slips to do outside - waiting on material. Ended up with triple glazing as suggested, made and installed by Wood Kraft in Elgin. Once the foundations were completed it took another 11 months before we were in. Spec Private water with our own borehole, mains gas, septic treatment plant. Triple glazed throughout MVHR Durisol walls, parge coated internally (sand, cement and lime mix) for airtightness, floor to wall junction with liquid airtightness paint, battons and plasterboard. External a mix of stone slips and Scottish larch. Posi rafter roof structure, battoned and counter battoned 100mm to give 350mm insulation space and then spray foam insulation. Passive House systems Reflective vapour airtightness layer, further battoned and plasterboard. Roof finished in slates and sarnafil EPDM standing seam and 3.1kw PV. Floor slab buildup, strip foundations with 100 to 150mm reinforced C34 concreted slab, 200mm of PIR insulation, UFH pipes throughout, at 300mm spacing, finished 100mm concrete with 70mm insulated perimeter. Work completed by myself Floor insulation UFH All plumbing except gas Durisol block work All battons to wall and roof Internal stud walls Parge coat Vapour control on roof internals (all ceilings match roof line) PV install, except electrical hook up Installed all bathroom s (x3) External cladding and currently doing stone slips. MVHR install Project managing and organising sub contractors who completed - ground work, roof structure, sarnafil and slates, electrical, windows, joiner for plasterboard and second fix joinery, taper for plasterboard. Images are a before and after

Take it you are in Scotland, I fitted GSE trays, tried to follow the instructions and they made little of no sense when working with sarking boards. If you add additional timber on the sarking the finished roof looks rubbish as nothing aligns correctly with the slates/tiles. The additional ventilation gives you a little uplift in performance, but not much to worry about. Screw them direct to sarking boards and make life easy. I had metal flashing at top and sides, flex stuff at bottom.

I bought from insulation hub, came direct from factory delivered to my door, delivery at no cost (NE Scotland) 400m2 of 100mm thick.

Reply may be a little late, but could help others. Are you trying to design around the slip or the durisol? When you are doing the lintels with durisol the blocks are on the end, so 500mm high and 250mm wide. The blocks either side of the window/door opening are modified to take the rebar. The window or door heights can be easily made to suit the slips, with too much additional work. The door opening, by the white box is 2100mm high, the open under the flattish roof, lined up with the blocks at 2000mm, both opening require blocks to be modified.

I chose an Atag A325ECX, it can take preheated water which increases the flow rate, have a thermal store upstream, cold water passes through the stores DHW Coil before going to combi. Store used as a buffer for UFH and has solar PV connected to immersion. So always sits at about 40 degrees. You can go open therm if you want, but have just removed and gone simple route, basic thermostats but with self balancing actuators on the UFH manifold and run UFH 24/7 at a low temp using a mixer and pump after the store.

It may be a bit late, but just commissioned a system similar to what you are looking at, here is what I have, after a few changes. Atag combi boiler, Telford thermal store (acting as a buffer with benefits) with boiler heating coil, DHW heating coil, mixing valve at outlet. Thermostat (middle of tank) set at 45 degrees, to reduce heat loss. UFH running at 30 degrees Solar PV Hook up, cold water to DHW coil, this passes through TS, and into combi, if it is hot or cold, the Atag boiler is designed to take pre heated water, so boiler doesn't care, the boiler only puts the energy it needs to the correct outlet temp. Upside, if preheated, you get great hot water flow. In the summer solar PV should do a lot of preheat. Have a secondary circuit, pump with simple timer at the out DHW outlet, so it can pick up hot water from TS coil or pass through the combi. Boiler was short cycling connected direct to UFH, so the UFH manifold now has mixer valve and pump added, this is connected direct to thermal store. Boiler connected direct to TS heating coil, boiler temp set at 50 degree. Advantages, boiler is always in condensing mode. Simple hook up, low standing losses as the tank is no hotter than 45 to 50 degrees.

That's good to know, we should get our first real prices this week.

Hi all Planning a new build in sunny Scotland, semi passivhaus, just wait for the warrant to be approved. There bed bungalow facing south west looking over a loch. House spec, floor, walls and roof U value of 0.1. Double glazed U value 1.2. UFH throughout. 3.2 kW solar PV, with immersion diverting. Thermal store heated by PV only to provide preheated water to Atag Combi boiler with full weather compensation. MVHR. Air tightness looking for around 1 m3/m2. Did the maths looking at payback for triple glazing and got pay back periods of around 40 years. Due to the low heat demand.