All the calculations were made for the standard, mental, MCS temps across rooms in the house but he quite rightly wants it to achieve 21c across the house with 22c in the bathrooms. Available space for radiator sizes looks like it is restricted in some rooms.  There may be some issue with microbore piping in some rooms hinting at "maybe need a buffer to achieve flow rate through these rooms which we'll have to determine during further investigation and site survey.  The Vaillant pump tends to offer less head room in which case we would include a buffer."  It's worth mentioning that they have stated that on any installation they would only include a buffer or volumiser where needed and they explained the purposes of both of these - in other words, it doesn't seem that they always bung these in for their customers because...  

From his bill he has an *estimated* 21,056kWh of annual usage of which approximately 2700kWh is hot water production.  I've struggled to get him to work out an actual usage value (perhaps I'm not explaining myself well enough) but it doesn't matter for the purposes of this question so much.  Given then the 21,056 - 2700 = 18,256kWh usage for heating: 18,256 / 2900 =6.295kW, approximately half the determined heat pump size, certainly within the range of a 7kW unit.

It's not clear exactly how he runs his gas central heating system but it would seem to be a couple of hours in the morning and a couple of hours in the evening; in winter it may get put on at additional times as well.

How accurate is the /2900 rule really and how does that reflect a more time slot-based usage vs say a boiler set to run 24/7 (controlled by the thermostat of course)?

Given there are nearly 7 million terraced houses in the UK maybe this is a missed opportunity.

With high ceilings and a layout which doesn't encourage sharing heat or cooling between rooms my ideal set up is a five port mini-split system. That gives indoor units in every room, i.e. the living room, kitchen, both bedrooms and even the bathroom. I'm lucky with the pipe runs and I've had a quote for such a system. The main downside was cost. To be fair I had an air to water quote that was higher, and that was after the £7,500 BUS grant.

I think in a way that's because the equipment available is just too powerful for my modest and well insulated house. My heat loss is calculated at about 5kW with the living room having the highest demand, roughly 1kW for 21C when it's -3C outside. However the best available system was a 9kW outdoor unit, indoor units would be ~3kW in the living room and ~2.4kW for all the other rooms.

I would certainly be able to let room cool when not in use and bring them up to temperature very quickly. Especially as with internal brick walls mean things actually cool very slowly. I wonder if there would be any problems associated with running the equipment so much under capacity? 

I think the minimum output was about 3kW so I expect the outdoor unit would have to stop and start a lot, particularly when demand is low i.e. October, November, possibly December, March and April. Does anyone know if that would shorten its lifespan?

I think what I need is about a 5kW outdoor unit with indoor units in the 1-2kW range. I suspect the only reasons they aren't on the market are historical ones where most of the demand is commercial. I'd be happy to learn differently.

One of my main objectives for a long time has been low running costs. Hence the insulation. Plus heating only when and where I need to or, in the jargon, zoning and set-backs. My yearly gas consumption for heating is about 3,000kWh. Which suggests with the actual temperatures I've been living comfortably with my heat loss is more like 2kW. 

Last November I ran my gas combi heating like an air to water system to see what that's like. While it was indeed comfortable my total energy consumption was roughly 50% higher than my usual 'extreme thrift' strategy. I doubt any gain in SCOP can offset that.

Which leads to another question. Would running an air to air system so much under capacity adversely affect the SCOP?

Actually I imagine not. I'm very impressed with the inherent efficiency of air to air systems. Its pure heat pumping, using phase changes and latent heat to full advantage. In part it's my physics background that rebels against air to water systems. What does a water heating circuit bring to the party? It's as if back in the 1950s when everyone kept food cool in a pantry someone said, "There's this great new thing called a refrigerator. Just stand this box in the kitchen and you can run a water circuit from it to cool down your pantry." Or you could put the food straight into the box. Not entirely fair I know.

Still one of the attractions of an air to air system for me is being able to rip out all the radiators.

i have since formally emailed Vaillant asking for the names of Vaillant certified companies both on Arran but also on the mainland.  I have had nothing back. 

i can probably get someone to do a service but, should anything go wrong subsequently, don’t want to be told “that company is not accredited” and find my guarantee is therefore void.

Can anyone suggest a way forward?

I have some questions about flushing my system, cleaning it and adding inhibitor.

I had a small leak in the system pipework, so drained the system down to fix it (longer story which I will also post about).

Bit of background, the system is 2 years old - everything was new apart from one old retained towel radiator and one small section of 22mm copper piping on the radiator circuit (maybe 5m total). All other pipework and radiators were new.

Whilst the system was fully drained, I took the opportunity to flush the system using the fill and flush loop. I closed all radiator valves and then opened one at a time flushing each radiator in turn until the water ran clear. The water coming out was orange brown in colour. I thought I was doing well, but once the system had settled for a while, if I flushed again more orange brown coloured water would flush out before running clear again. Is this normal, is this colouration from rust? Should I keep flushing? Picture of sample of water after much flushing below (ignore the black floaty bits which were in the container before).

I've bought some Sentinel X400 cleaner and X100 inhibitor. The instructions say the X400 cleaner should be circulated for a minimum of two hours at normal operating temperature and can be left in the system for 3-4 weeks before draining and refilling with the inhibitor. As the heating will not be back on until October, should I add the X400 cleaner now, and just circulate it around the system (radiators) for 10 mins per day as the heating is not on, or should I wait until October before adding it at which point it can work in a heated system? It will get circulated through the primaries and ASHP for 30mins per day during DHW cycles. The heating only ever runs at 32C LWT in October, so maybe not a huge difference to just pumping cool (25C) water round the system now for a few days to clean? I don't expect the system to be full of sludge so it's really a case of just wanting the system to be as clean as possible before refilling with inhibitor and being good to go for the next couple years.

If I don't add it until October, will my system be OK running for two months (DHW only) with just water and no inhibitor?

We are in a soft water area.

We are just starting our heat pump journey, we have a 1962 build 3 bed detached house which has the usual large windows. We did a fair amount of upgrades done when we moved in 15 years ago, re wire, replacing an old floor standing gas boiler with numerous radiator changed from poor performing ones new hot water cylinder and moving to a sealed system, A classified double glazing etc. We have solar and 10kW battery storage and run 2 ev’s.

We have had someone from ARIA to do the initial pitch, lots of videos, slideshows etc and an initial estimate subject to survey. Main concern is their design includes a buffer tank which seems a bit overkill and watching numerous YT videos question their use. Current recommendation is a 6kw outdoor unit and 250l cylinder.

Heat Geek certified installer coming on Monday to do a survey so should get an idea of heat loss and a better idea on cost over initial online estimate.

Did the initial online quote with Octopus, energy provider, requested a call but currently finding it impossible to get anyone to talk to me. Was hoping to get a rough idea of amount of energy used by their heat pumps to get an idea if it is worth increasing my solar battery storage.

Looking for any recommendations for the Reading area for us to consider as it looks like we won’t be having Octopus through the door now.

Sorry for the long intro.

Cheers

Ian

I also worry about AI interactions if a homeowner has, say, a Powerwall and is on an Octopus tariff such as Intelligent Flux or Cosy. I am not sure how all these integrations will work together.

Thoughts?

Your heat pump data is in one app. Your design documents are buried in email. Your maintenance history is somewhere else. Your performance figures might be in a spreadsheet. Your solar, battery and tariff information live in completely separate systems. Then, if the heat pump is replaced, years of useful history can effectively disappear with it.

That is the problem HomeTherma is trying to solve.

HomeTherma is a homeowner platform designed to create a long-term record of your heat pump, your home and, increasingly, your wider home-energy system.

You can use it to record your property, heating system, controls, emitters and hot-water setup; track performance over months, seasons or years; keep a Timeline of changes and upgrades; store documents; manage maintenance; and build a historical record that survives when equipment is replaced.

The deeper you go, the more useful it becomes. HomeTherma can use the information you provide to give context around performance, highlight useful gaps in your record, support comparisons where enough relevant data exists and help you understand what may be worth looking at next.

It is not designed to diagnose faults or replace a heating engineer. The aim is to make homeowners better informed and give them a much clearer picture of their own system.

And it is not just about heat pumps forever. HomeTherma is built around the home itself, so tariffs, solar PV, batteries, EVs and other energy technologies can become part of the same record over time.

Who is it for?

If you own a heat pump and have ever thought:

“I really should keep all this information somewhere.”

“I have no idea where that commissioning document went.”

“I know my system is performing differently, but I cannot easily compare it with last year.”

“I changed something six months ago and now cannot remember exactly when.”

“I wish all of this lived in one place.”

…then HomeTherma is probably for you.

There is a free version, which lets you start building the core record of your home and heating system, track basic performance and preserve your system history.

Premium adds the deeper stuff: Documents, Insights, Benchmarks, Annual Reviews, Energy, Maintenance, advanced performance context and system comparisons.

HomeTherma is still in beta.

That is important. There will be bugs. Some features will change. Some things will undoubtedly need simplifying, improving or completely rethinking as more people use it.

And that is exactly why I am opening it up now.

For the early users who come on board during this beta period, I want the relationship to work both ways. If there is something you think HomeTherma needs in order to make the product genuinely useful for you, tell me. Feature requests and suggestions from early users will get priority while the platform is still being shaped.

I am not interested in building features because they sound clever. I want to build the things homeowners actually use.

To encourage a few more people to get involved at this stage, I am also running an early-adopter offer.

For a limited time, you can get 75% off HomeTherma Premium for life.

Simply use code: EARLYTHERMA

The normal Premium price is £39.99 per year. If you subscribe using EARLYTHERMA during this offer, your 75% discounted rate stays with you for as long as you keep the subscription active.

This is very deliberately an early-user offer. You are getting a substantial discount because you are joining while HomeTherma is still being finalised, tested and improved.

If you do sign up, please push it to the limit. Tell me when something makes no sense. Tell me when something feels unnecessary. Tell me when you think I have missed something obvious. And equally, tell me when something is genuinely useful. There is a full support system for posting tickets.

That feedback is going to shape where HomeTherma goes next.

You can take a look here:

https://hometherma.co.uk/

See you there.

I’m still trying to get my head around heat pumps and how much difference the settings really make to running costs. There seems to be quite a lot of conflicting advice, especially around flow temperature, weather compensation and whether it’s better to let the system run steadily rather than turning it down for parts of the day.

For those who have had an air source heat pump for a while, what changes have made the biggest difference to your electricity usage?

I’m particularly interested in real-world experience rather than manufacturer figures. Things like changing the flow temperature, adjusting the heating curve, improving insulation, or changing the heating schedule.

Also, has anyone found that a small change in settings made a surprisingly big difference to comfort or efficiency?

Would be really interested to hear what has worked (or not worked) for other owners.