marshian

I fitted a PIV unit centrally in the house (4 bed over two floors) as a result of humidity levels spiking after I insulated under my suspended ground floor (great idea from a heat loss perspective but it had clearly been a major contributor of uncontrolled air ingress) Within a few days the PIV unit had brought the house into a level of control initially on a higher flow setting but now it's on a timed schedule (midnight to 6.00 am and 8.30 am to 3.00 pm as this works for our occupancy routine. I did buy one with a heater but 400W consumption can rapidly increase electricity usage when it cuts in so I've got it turned off. I do have trickle vents in a few windows (not all because most predate the requirement) but a fair percentage of the air pushed into the house is ventilated out via bathrooms fan extracts even when the fans are off. (this is exactly what I need as dry air expels the warm wet air in bathrooms) Overall it works well for us

Current winter daily average HW heating is 4.5 kWh at £0.052 per kWh No solar, no battery and std fixed electricity rate at £0.26 per kWh - be a big increase in cost to heat direct via immersion only We only ever heat direct in summer during heating system improvements (have some more planned for 2026)

Good teacher 😉 I would have never thought to look for one on auction sites (figured they would be all unsuitable cyl's removed as upgraded from heat pump installs so no real advantage for me) Retail appears to be just over £1,000 Slightly cheaper than going with PHEX unit and pump but suffering the same heat losses from my existing cyl A lot cheaper than converting a direct cyl with a PHEX and pump. Manufacturer claims at a 58 deg flow temp coil output is 8 kWh so my 30 min HW re-charge should still be possible even with a little more capacity I think my HW coil size is probably tiny in comparison (would have been designed for high flow temps) best guess less than 0.5 m2

Right inspired by @JohnMo's bargain hunting I've been looking for a replacement HW tank Criteria/Requirements Unvented (but must have manufacturers approval to be installed in vented configuration) 150 Litres Max (Space restrictions and it meets the household needs from a daily consumption perspective) Immersion heater at the base (this is fairly std) 2m2 Coil surface area (I'd like 3 m2 but it seems tanks below 200 L are typically 2 m2 and only at 200L do they go up to 3m2 coil and I don't want a 200L plus tank) Eventually I found one brand new but ordered in error for what looked like a decent price Unvented 150L, 2 m2 coil surface area, immersion in the right place, but didn't want to make an offer until I had contacted the manufacturers to check if it could be installed in a vented set up (reasons are covered earlier in the thread) Made a cheeky offer and £450 it was mine just got go fetch it now

I'd put a PIV unit it and just run it over night - you could probably run it on the lowest speed (2 W consumption) and at that rate it's not going to cost much at all to heat the incoming air We run ours on setting 3 overnight (7W) so that's 30 Litres per sec in a 291 m3 House volume it gives us an ACH of 0.37 We have tried it on a lower speed but we get condensation on the inside of the windows in the main bedroom so we'd rather have a higher ACH and no condensation and a little more energy spend heating the cooler air that is being forced into the house

Hmm that's interesting - Thank you A double version of what I currently have 1600 x 472 has an claimed output of 1579 w I could easily increase the height to 1800 x 472 and that has a claimed output of 1750 w It seems neither will get me to target (closer but no cigar as they say)

I'm debating upgrading the two bathroom rads They are verticals - I purchased them in 2023 when I was still using the previous glow worm boiler that couldn't cope with a flow temp below 45 and I had to fit aftermarket diverters to make them work properly (picture below was from a thread on rubbish quality rads) Last winter I was transitioning from scheduled heating at higher temps to 24/7 with weather compensation so the bathroom temps were a lot warmer Now I've been running flow temps in the winter of low to mid 30's the bathrooms only reach 21 deg C - personally I find that OK but Mrs Alien feels that they need to be warmer (she does however like a long bath. They are rated at 0.89 kW at T50 - heat loss of the bathrooms is pretty much identical at 220 w What I'm trying to get my head round is how much larger a rad I need to get to a target of 23 Deg C with my current flow temps (I know I can get a double version of the on I have and Mrs Alien is happy with the asthetics.............. The current rads wouldn't go to waste as one could replace a towel rail rad in downstairs toilet and another in the utility room (both the towel rails used to be in the bathrooms but couldn't get the rooms to temp at 45 deg flow temps so were relocated to replace 1980's single panel single convectors rads rather than wasted) The utility room in particular has additional heat sources, tumble drier, Freezer, Fridge and washing machine so needs very little additional heat I might ask ChatGPT to see if it can work out what wattage I need to hit 23 seeing as that's the current trend for everything PS No the rooms wouldn't be continually heated to 23 - I'd manage the rooms temps with a setback when not bathing!!!

Avg energy consumption was 3.81 kWh Total Consumption was 38.1 kWh (38.1 divided by 10 hrs)

OAT overnight -4.4 Deg C highest temp in the day -0.2 Deg C but it wasn't there for long All internal room temps held nice and stable Boiler ran from Midnight to just before 10am with one burn (it finished that burn just before the HW cycle was scheduled probably due to OAT warming up or the modulation blips threw the flow temp over target. Avg energy usage for that period 3.81 kWh That's quite impressive considering the modulation hiccups it has on a regular basis Looking like my heat loss calcs are a little more than actual ~4.25 kWh @ -2.5 OAT From my Octopus account Gas usage over the 24 hr period Overall the whole day saw the boiler do 7 cycles (normal is 20 to 24) Bloody modulation blips annoy me still..............

It really depends on age - both my Loft tanks (CW and F&E) have ball cock controls that are 45 years old - they've had between them 2 washers in 30 years - the whole thing takes 5 mins to strip down - it's all brass construction and will probably outlast me Most modern plastic stuff is crap - made to a price point and doesn't last long If it isn't an old brass unit I agree replace the whole thing and stick an isolation valve in the feed so the next time it needs replacing you don't need to turn off the water supply to the house

Oh that's rather neat but I have a question, related to it When I did my heat loss with an on-line process (heat engineer software) I used the internal wall measurements but your sheet seems to require external wall dimensions - is that normal practice?

Hard water area? Ball valve sealing washer is worn (or gone hard)

Similar here OAT overnight -4.4 Deg C All internal room temps held nice and stable overnight Boiler ran from Midnight to just before 10am with one burn (it finished that burn just before the HW cycle was scheduled probably due to OAT warming up or the modulation blips threw the flow temp over target. Avg energy usage for that period 3.81 kWh That's quite impressive considering the modulation hiccups it has on a regular basis Looking like my heat loss calcs are a little more than actual ~4.25 kWh @ -2.5 OAT

Perfect summary

House is 1/3 of yours 113m2 however it is a stupid T shape with many rooms having 3 external walls which in a 1980’s house hurts. what I would say however is heating 24/7 with or without setbacks for me is actually not much of an increase on heating via a schedule with much higher flow temps for shorter periods morning and night - house temp swings were dramatic - far too easy to overheat the house and it never felt as comfortable as it does now. (Less than £50 a year from memory) what really triggered the move to 24/7 was that I would run the CH at the weekend all day and Monday would always be really low usage compared to the rest of the week - simple when I thought about it - I’d warmed up the internal fabric of the house over the weekend and on Mondays it gave it up again…..