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Next year I plan on replacing our aging boiler with a heat pump, but first some background.

We own a two story 1970 detached house in the south east, approximately 175m2. The original house was built without cavity insulation, it was added in 1975, on the certificate it states it was insulated with Superfoam Cavity Wall Insulation, best way I can describe it is it looks like snow. It's probably a bit hit and miss, certainly upstairs the top foot of wall isn't insulated due to the inner leaf being higher than the outer leaf. Rather annoyingly I had scaffold up along that side over the summer, even had some of the roof off, hence why I know, but being tight on time I didn't think to do anything about it. Double glazing was installed in 1999 by Brightlight, some sealed units have been replaced, some more need doing. The extension all had double glazing installed, but it was nothing special.

In 2004 we added a large side extension, this was built with cavity wall insulation, and the single story kitchen extension done with a warm roof and plenty of Celotex, which I personally refitted as the builders left gaps I could get my hands in! Loft needs some attention, there is at least 150mm and some parts have 300mm of insulation.

The entire heating system was replaced around the same time the extension was built, all of the work apart from connecting the gas and commissioning was done by myself. I used a Greenstar Highflow 440, which is a huge floor standing boiler, it's now almost 20 years old. I zoned the entire house, pretty much every room is its own zone and has its own Heatmiser thermostat. 12 zones in total. These zones are split into two groups of zone valves, so the plumbing goes in two direction from the boiler to the two groups of zone valves.

It gets worse, on the original house I used 22mm plastic (all John Guest) for the main run to the zone valves, and then 15mm plastic to the rads, final connections done in 15mm copper. The extension was all done in 22mm copper to the zone valves, and then 15mm copper. Obviously being fully zoned each rad has its own feed, not so sure on the returns though, I need to check this. I know the two biggest rads on the plastic have their own returns back to the 22mm pipe, and I think the rest will be at most two rads on one 15mm return. Something I need to look into further though.

Over the last month I've been adding monitoring to the boiler, and also individual room sensors, and last weekend I spent quite a lot of time changing all the buttons on most the thermostats, as they didn't work. I've now got the boiler flowing around 45c, the thermostats are all set for the same time, and basically the same temperature. All rooms seem to heat OK, apart from one that's always been a bit colder, I have improved it recently, but it still consistently colder. Generally the house now feels warmer, and I'm pretty sure is using less gas.

We have a total of 15.5kWp of solar, and 29 kWh of storage, our energy (gas and electric) costs have been negative two years in a row now, next year will be a lot more negative as I added an additional 6.795 kWp of panels in September.

I know how you all like some pictures so I'll post some shortly.

PV System.

In 2015 we had a 4kWp SolarEdge system installed, 8 panels pointing ESE and 8 SSW. In 2022 I decided to add another 4.74kWp to our double garage which were finally installed in early 2023, a total of 16 panels, 8 pointing ESE and the other 8 WNW. I also added an 8kW Quattro 48/10000 and two self built 14.5kW batteries, to give whole house backup. But alas that was still not enough (is it ever), and I kept looking out empty SSW facing wall which gets sum all day when its out, and a large unused WNW roof. So another 12 panels 435w panels went on the roof, and three 525w panels on the wall. That's a total of 43 panels and 15.535 kWp.











So electrical power is sorted.

Which brings me on to my next project, and why all this solar stuff is in the space heating thread.

I want to replace our aging boiler with a heat pump. To improve comfort, to lower costs, and do away completely with gas, we fitted an induction hob a few months back, so gas is purely used for heating. We do have a large wood burning stove, which has its own external air supply, although to be honest we very rarely use it. Picture below is from Christmas 2021, think the last time we had it on was Christmas 2022, last year it just wasn't cold enough.



I am planning on using an installer, but want to get a good understanding prior to engaging with them next year. Unless the cost turns out to be horrendous I plan on using one of the two local Heatgeek installers. I'm not planning on very high SCOP's, I think around 4 is easily doable, and with our large battery capacity should mean for the most part running off cheap rate electric.

Boiler temperatures, this is just with a Shelly sensor attached to the pipe with insulation over it.



Room temperatures using Aqara temperature and humidity sensors, bottom trace is an outside sensor on the garage, next one up is my daughters room, the coldest room in the house.



Room humidity



The original windows don't have trickle vents, so I've bought some to fit. The smaller opening window in my daughters room is 1130 x 260, so even having it open in the vent position lets a lot of cold air in this time of year, this sealed unit is also blown so I need to replace that.

ANyway, I've been summoned to sort out the back bedroom for my other daughter, who's coming home for Christmas, so will add further info later.

You can range rate the boiler to reduce the output…

I have the 550

Impressive work

AGT wrote: ↑Sat Dec 21, 2024 2:49 pm You can range rate the boiler to reduce the output…

I have the 550

Thanks, but I can't see anything in the operating or installation manual, mines not a CDI, it was purchased in December 2005, so 19 years old.

Think the newer 440 and the 550 came out around 2008 to 2010.

dan_b wrote: ↑Sat Dec 21, 2024 3:12 pmImpressive work

Thank you.

Looks great, very nice set up.

From my recent install, make sure the heat calc is detailed and takes a couple of hours.

Ensure HP has plenty of open space around it.
Go big on the pipework, remove as many restrictions as you can.
Check all the pipe insulation especially on the bends. Armaflrx will split along the seam under pressure on a 90 deg bend.
Bedroom thermostats are great!
The time and effort you put in now will be a large part of your end result for the next 20 years.
Ask the installers what the minimumn scop they promise.

Looking forward to watching your adventures. Everything good I heard about these systems is true. I've seen nothing negative apart from you cannot have your HW and space heating on at the same time. As the home is acting as one big storage heater you won't notice the heating being off for a wee but while the hw charges. Thought I'd mention it as it was a surprise to us but that was due to old way of thinking.

Going outside isn't as much fun as it used to be.

The problematic bedroom, "A's Bedroom" in the above charts.

It's quite a large room with two external walls, 3230 x 4400 (2.3 meters high), its actual floor area is quite a bit smaller as it has built in floor to ceiling wardrobes. It has a fairly large window at 1820 x 1060 which is NE facing, with one of the sealed units being blown, not sure how much that will affect things, but its on the list to change.

Just been up and measured, and the insulation is around 200mm above it, I thought this had 300mm, so that needs improving, and the bit I thought was around 200mm is actually less, so that certainly needs doing, guess I need to tidy the loft and put in some more insulation up there.

Thermal image of A's bedroom.



We have 2200 x 450 K1 radiator in there, which Heatpunk thinks is big enough for a 40c flow temperature, depending on how the surveys go I'll probably fit the redundant 2000 x 450 P+ from the dining room which is undersized for 40c flow.

Hopefully once the blown sealed unit is replaced, and loft insulation increased that will help, only other thing I could to is line the LH wall with insulation backed plasterboard, but that's really not something I want to do.

Whilst I'm talking about loft insulation, some more thermal pictures, just goes to show how heat can escape.

Ronski wrote: ↑Sat Dec 21, 2024 3:22 pm

AGT wrote: ↑Sat Dec 21, 2024 2:49 pm You can range rate the boiler to reduce the output…

I have the 550

Thanks, but I can't see anything in the operating or installation manual, mines not a CDI, it was purchased in December 2005, so 19 years old.

Think the newer 440 and the 550 came out around 2008 to 2010.

dan_b wrote: ↑Sat Dec 21, 2024 3:12 pmImpressive work

Thank you.

its not in the user/installation manual you get with the boiler, its an engineer manual that's available from WB, will try and find the name

nice work on all the work

So I've been playing around with heatpunk for a while now.

Think I've got everything as close to what I can, given its a 50 year old house, with unknown quality of wall insulation, some 25 and some 20 year old windows neither of which I know the U value for, its been rather hard to guess the correct U values to use. I know the construction, I've knocked enough holes in it over the years, its just the finer details that are guess work to a certain extent.

Anyway, heatpunk recons we have a heat loss 6916w at -3.2c, so a 7kW Aerotherm Plus should be sufficient. It also says our total annual demand is 16967 kWh a year, which seems at odds with our actual gas usage.

Our annual gas usage for 2023 was 9099 kWh, that was for heating, hot water and our gas hob.
For 2024 up to 19 December was 8587 kWh, gas hob was removed in July

Any thoughts on why heat punk differs so from much on past actual usage???

Next question I'd really like thoughts on, we have a combi, the cylinder was ripped out 20 years ago, we still have the airing cupboard, with a little radiator and plenty of shelves. I know the Mrs won't be happy if the cupboard is filled with a cylinder and all sorts of other gubbins, with no room to put stuff.

It is a big cupboard though 1 meter by 650mm and 2.3 meters tall, but I don't want the cylinder there, I don't want it in the loft either. Both locations would give circa 16 meter run to the kitchen tap.

The boiler is currently in our utility room, its relatively easy to get pipe from outside in the most likely location to where the boiler is. It's also central to all three places hot water is required, BUT space is limited. The current floor space taken by the boiler is 600 x 600, more depth is available.

I've seen that Valiant do a uniTower, this should fit where the boiler is, so I have some more questions.

It's only has a 190ltr tank, there is only three of us here full time, but it is a five bedroom house, would this be sufficient, a difficult question to answer, but what are peoples thought?

Could we get a bigger tank and all the other gubbins in the same space? This seems unlikely as most installs seem to really spread out, which is not something I like.

Here's a screenshot of a spreadsheet I've been working on. I've no idea of the heat output of the towel rails in the two bathrooms, and wonder if I'll need standard radiators fitted, and then fit a rail above that, so the rads don't get covered.