JohnMo

Spend last year learning about our building inertia when heating, and fixed a couple of issues with the buffer plumbings. So now the boiler (min output 6.7kW), keeping house at an almost constant 20 degs. UFH flow temp is 23/24 degrees during the day, boiler kicks in for about 10 mins every hour or so. Night setback starts at 1830 hrs and goes back to day setting at 0230 hrs. Working pretty efficiently, on average using 19kWh per day for 194m2 house including DHW (about 5kWh) Against a theoretical 26 kWh for heating only, at our weather conditions using Jeremy's spreadsheet. If I was heating with a heat pump with a CoP of 5, that would be 3kWh a day for heating only. Super cheap.

You would have to compare that with direct electric heating. To get a pay back time. So direct electric heating has 100% efficiency. Say gas is 85% efficient. Gas effective gas about 12p, electric 34p Then it depends on central heating cost to install compared to panel heaters at the cheapest, or cost for UFH with immersion heater. Plus DHW heater. And how much energy you use. So for a like for like comparison system boiler, and UFH and hot water cylinder £600 -1000 for a boiler, immersion for UFH £60. So say 10000kWh per year. 0.12 X 10000=£1200 0.34 X 10000=£3400 So in that case not long even with an expensive boiler. A combi gas boiler would delete the cylinder, so pay back shorter again. As it costs an extra £2200 per year to pay for electricity. In this case even comparing panel heater to full blown central heating, pay back is a year or so. 20000kWh £2400 and £7400. Very low user 1000kWh £120 compared to £340, so a couple of years. Economy 7 changes the maths, but you have to also pay for storage heaters.

If you can run Weather Compensation, do you need a room thermostat, just balance the flow rates to get the room temp you require. If you have thermostats in the room, use simple ones to call for heat, but use them as limit stops, instead of a thermostat in the normal terms. So if the WC is set to give you 20 degrees, set the thermostat at 22.

Not really, as gas is not 100% efficient, most gas boilers achieve around 85% efficiency, especially if not run on weather compensation as a single zone. So you need a scop of 2.8 to match gas.

You basically in theory should start at at flow of about 25 and every 24 hrs increase the temp 5 degrees until you get to 45. If you are well insulated, your flow temps should be low. Our max flow temp is 28 at -5 outside. So I just started it up, plus our concrete had been on place for a year or more.

At the moment you have a nice thermal bridge, I would also be concerned about condensation forming at the sole plate. I have a typical Scottish strip foundation, with blockwork coming up from the foundation. I modified mine with full structural approval. Slightly different ICF build but the principals should be the same. Your soleplate fixing could no longer be central, but be staggered between the inner and out blocks. Total width 365mm Inside block 100mm thermolite Cavity filled with 100mm PIR - size to suit width required. Outside block 150mm concrete block. Inside all that I used a 70mm PIR upstand from the floor insulation, inside that is concrete screed 100mm deep.

Not really believing you are doing this without structural engineering input. Or if have it, not following what they are saying to do.

Ask Domus, for an agent by you

Will this be big enough to start it?

When I did my internal walls, I just used large scissors. I think people hate it, because it makes you itch, cough if you don't wear overalls, gloves, glasses and face mask, if you do wear the safety gear you sweet buckets in a loft.

Pretty pants for triple glazing. Let down by the aluminium frame. You can get double glazed that performs as good or better if you are using krypton gas.

Joy of Scotland, temperature may not be as good, but water meters are rare.

Any garden watering?

Used muck munchers. https://www.muck-munchers.co.uk/ Although the treatment tank had been working for a year, when the outside air was still, the air vent would allow a stench to drop down. Within a couple of days of using muck muncher starter kit, no smell. One month later no smells and have just used a monthly top up. £40 for starter and a year's supply of top ups.

Your SAP is representative of having 50m2 of solar, not really being passiv or an airtightness of 0.18. just about any house with 50m2 would be over the 100 SAP score.

You cannot just pick a flow temperature and assume it will work. Flow temp depends on heat loss, both from the house and downwards. You really need to be looking at running weather compensation to get the best CoP. See attached, the red lines are there as examples. You need to calculate your heat loss then find W per m2. From these charts you can calculate your heat for WC. Find heat loss at -20 and +20, convert them to flow temps and plot a straight line curve. You need to consider the min flow requirements of the heat pump and let that guide you on centers. Also the centre distance affects the response time of the floor.

Be careful with fixings in the end grain as the pull out resistance is low.

The structural details from our structural engineer

SAP is still based on old values for embedded carbon within electric generation, so gas wins with SAP scores. U values look fine. So where you can improve is against standard details, that remove thermal bridges, these are lintels, windows and door returns and heads. So something to investigate. All low cost attention to detail. Also airtightness, assuming you haven't given SAP an airtight target. Again doesn't need to cost a lot, needs detailing early on and watch execution. Things to watch with airtightness. Anything better than I think 5 would drive you to MEV or dMEV, better than 3 MVHR. Ventilation without going the MVHR would be better as a demand based MEV or dMEV system. So something else to look at. Other things are heating controls, certain ones will improve SAP score.

Looks good, nice usable size.

Agreed. Heating, just set up weather compensation in my house after failing last year (long story). Below 12 degrees outside heating come on its own, super low flow temps, no need to switch on off, so why would I need a home automation system for that. Although I have thermostats they are not really needed. Electric towel rads, a simple timer thermostat. Lights get switched on/off as I walk in/out the room. Ventilation system just runs in the background, so need to mess with that. Has humidity sensors which are hit or miss, so just use boost switch. Tried cameras in theory great, in reality complete pain, not liking our WiFi, so now in my do it later pile (ie never). So PIR on outside lights is about as smart as I intend to go. No home appliances, lights, heating or ventilation connected to internet. TV already comes with a really clever IR remote, why pay to replicate it on another system.

Good work. But - Not keen on your prison window. My wife would throw a wobbly if I even proposed doing that. Not that I would.

81 B, isn't that good. What are you U values, they will be in the report. How is the house constructed. With UFH you need a good, low U value, otherwise you will be paying to heat heat the earth below your house, as much as your house. There may be things you can do to increase your rating easily and relatively cheaply.

I am using a combined grille on the gable end, seems to be working well. Less stuff going through the roof. https://www.paulheatrecovery.co.uk/product-category/mvhr-ducting/terminals-external/

I bought mine of gumtree, 5x for £50, sold two for £50, installed one on bedroom and another in the lounge, one spare. Amazing what you can find