Heatgeek.com

22mm will run 6kW at a DT of 5. 15 will run 2.75kW, and 10mm will run 1.15kW.
If the 22mm runs for a way, then splits to upstairs and downstairs in 15mm, then it may be OK with the existing pipes.
If there is only a small section of 22, and large runs with multiple rads in 15mm, then you will not get a well run system, as the DT will need to be larger (the difference between flow and return), and having a larger DT means more electric to heat it up.
See what your heat loss survey says, it should have room by room details, if you can find out which pipe feeds which room, you can then work it out to see if any pipes need changing. For example, if the living room heat loss is 2kW, and you have a 10mm pipe running to one large rad, then it isnt going to be efficient, as 10mm will only comfortably run 1.15kW. You can get it to work by running the HP at a higher temperature, and increasing the DT, but that knocks efficiency, whcih shoudl be designed out to get the best and cheapest running system.

I don’t know where all the pipes go. I just opened up the kitchen ceiling to lag the (15mm) from one side to the other and I saw both 15 and 22 so I am guessing that it is as you say – that would seem logical, but who knows.  When you say DT in that sentence do you mean the drop across the pipes before it hits the radiators?

I’ve got the boiler set to 40C, which means it will top out at 45C. I haven’t measured the temps yet because I have lost my thermometer but the hottest rad is about 42C or so once it’s reached max temp  using the IR probe.   I can’t measure the outflow but based on this and what I have exhaustively measured before the boiler return will be about 30C or a little less. It’s certainly only a little warm to the touch.

Most rooms now have 100mm type 21 radiators, the living room has two. It’s certainly toasty in here now as the heating has just cut out having come on earlier.  I’m working on the assumption that if 40-45C flow temps can add 1C in half an hour, then 35C should be able to keep it topped up most of the time if run continuously.

We’ve got someone coming round tomorrow night from a Heat Pump installation company to do an assessment at our bungalow. What questions should I be asking? We already have solar power and, with 2 of us living in a 5 roomed house, our bills are pretty low. I’m looking to be convinced of the need to spend another big chunk.

^^^ Anybody??

You can ask them as many questions as you like, whether you get an answer that is truthful or that you fully understand may be difficult.

As always the best information will be if you have seen their work or know other people who have used them.

But ask them how big their company is, how many installers (employed and sub contracted), do they carry out servicing and maintenance, which units they fit, the number they fit per year (try to judge how many they should be installing compared to the size of the company). Types of system they install, air source only or ground, closed loop, open loop, cooling options. Workmanship warranties.

I would suggest if they only fit air, and Daikin, Samsung or cheaper heat pumps in big numbers with lots of sub contract labour then I would avoid as they are picking low hanging fruit just looking to make as much money without offering any aftercare.

If a company is prepared to maintain and repair then hopefully they will carry out a reasonable install as they are looking after it for you.

Feel free to message me if you have any queries.

Ask whether their kit is Kraken compatible for when Octopus take over the universe. I personally paid for a propane heat pump on the basis it is more efficient in cold weather than a standard R32 or R400 series refrigerant. We are still getting a CoP of about 6 even with temperatures dropping to near zero overnight.

A couple of bits dud annoy me about our install though. The first being that we had to replace a perfectly fine 250litre Worcester Bosch hot water tank as they wouldn’t guarantee the system without replacement. The existing tank had as good insulation and basically the same coil area as the new one. Grr.

Second point was that they ended up having to run large bore (mebbes 30mm) pipes to and from the heat pump up into our loft to the balance tank they also installed. I know that the heat pump circulates hot water at a quicker rate than a gas boiler, but why don’t they just stick in a more powerful pump so it copes with the increased pressure drop? It means we have two ugly lagged pipes running up the entire side of our house, instead of them just popping through the wall to the conveniently placed supply and return pipes from the old boiler. Also Grr.

edit – others more relevant

Thanks all. Appreciated. We’ll see what they have to say. ?

Second point was that they ended up having to run large bore (mebbes 30mm) pipes to and from the heat pump up into our loft to the balance tank they also installed. I know that the heat pump circulates hot water at a quicker rate than a gas boiler, but why don’t they just stick in a more powerful pump so it copes with the increased pressure drop?

It’ll be 28mm probably, or, 35mm pipes. They need to be that size to be able the transfer the heat at an efficient level. Gas boilers probably run the water at a similar speed, it is the difference between the flow and return temperatures that determine the pipe size. Gas boiler have at least 10 degrees difference between flow and return, and usually 20 degrees. Heat pumps want a 5 degree difference.
Because of the small difference, it impacts on the heat given out by the radiators by both having a lower flow temperature, and the flow/return being a lot closer. Yes, pump speed can be increased, but that causes more problems. The typical pump speed is 0.9 metres per second for a well deisgned system. It can be a bit either way, but 0.9mps is a good compromise. If its slower, the flow/return temps will have a larger spread, as the water is out at the rads for longer, but less heat is put out, as the water speed cannot transfer all of the heat from the heat source. Doubling the pump speed increases the internal pipe friction by 4 times,the pump consumes 8x more power, it can get noisy, and will wear out quicker.
So, keeping 22mm piping (at more than 6kW output power) will limit the output at the Heat Pumps most efficient range, and is pretty much a Manufacturers requirement, as all of the ones I’ve dealt with require a minimum of 28mm primary piping. Sticking it on 22mm piping will invalidate any warranty if it ever goes wrong.

Coming up to a week after signup now (tomorrow). I’ve had an ‘Introducing’ email for the installer from HG but radio silence from the installer themselves.