ASHP with 8mm microbore

[PT1984]

Does anyone have hands on experience with a ASHP with 8mm microbore rad tails.

We are getting the keys to our new (late 70s) house at the end of the month. Ignoring the insulation discussion for now.

What I know is it’s a unvented system with two tanks in the loft. HW tank in the upstairs bathroom cupboard. Relatively new WB 18i in the garage with a Magnaclean.

22mm flow and return to the boiler. Can see these next to the tank with valves etc. 15mm cold and HW pipes.

No idea how the 22mm backbone runs, but it’s not a big house. I’m picking up a thermal camera to try and trace.





The wife cares little for this stuff. She just wants new carpets in. I suppose pulling boards upstairs to replace with 15mm will be manageable. Downstairs I imagine will need chasing in. FYI all rads were previously the single side double valve type. I assume then both flow and return will drop as a pair?



Most, but not all have had these changed just extended either the flow or return.

So. For those with 8mm microbore. Has a ASHP worked to provide you with both heat comfort, and economy / good SCOP?

[gmaz]

I've just had a survey from Octopus and they insisted on at least 15mm CH piping, so I think the microbore will need to be changed if you get an ASHP.

I also had existing 22mm piping from the gas boiler, but the surveyor said that would need to be changed to 28mm between the ASHP and unvented cylinder.

I'd highly recommend Octopus for the HP survey, they charge £200 (refundable if you sign up for the install) but it is a very comprehensive and detailed job.

If you want £100 off, email me for a referral code.

https://octopus.energy/order/heat-pump/

[PT1984]

Thanks for the offer. However that looks pretty conclusive. Others have just a no problem with a volumiser!

[langy]

I think this answers my question on another thread. We have 10mm radiator pipes and have just had a fair amount of work done downstairs including installing new radiators with 10mm pipe.
No ASHP for me….

[gmaz]

PT1984 said:

Thanks for the offer. However that looks pretty conclusive. Others have just a no problem with a volumiser!

I'd still recommend getting a quote (free) and a survey done (£200), they may be able to find a solution within your budget.

[chrismoose91]

langy said:

I think this answers my question on another thread. We have 10mm radiator pipes and have just had a fair amount of work done downstairs including installing new radiators with 10mm pipe.
No ASHP for me….

All my rads are on 10mm copper, Octopus ASHP, no issues.

[scot_aln]

Out of interest is there a reason for the switch to an heat pump if the current boiler is relatively recent.

[carinatauk]

Might be useful to have a chat with Heat Geeks. They have loads of Youtube videos worth watching.

I had the same discussion with one installer and two other ones with other installers. I have been told that it is entirely possible with microbore, but in fairness I didn't really understand it

[Patio]

If you're having to rip out all the connecting pipework would it not be worth doing a cost comparison of retro fitting UFCH and doing away with the rads?

Ufch is more efficient and free the walls up from ugly rads

[PT1984]

scot_aln said:

Out of interest is there a reason for the switch to an heat pump if the current boiler is relatively recent.

I’d be happier with 10mm. But 8mm flow is significantly less.

[PT1984]

scot_aln said:

Out of interest is there a reason for the switch to an heat pump if the current boiler is relatively recent.

In the first instance I would want to future proof the system. And I’d rather do it now before carpets go down.

[PT1984]

Patio said:

If you're having to rip out all the connecting pipework would it not be worth doing a cost comparison of retro fitting UFCH and doing away with the rads?

Ufch is more efficient and free the walls up from ugly rads

My thoughts are switch to 15mm upstairs. That should be relatively easy. Then live with 8mm downstairs until we knock the walls out, and decide where the kitchen cabs will go.

[thepritch]

We moved into a granite cottage in Scotland in the winter. Soon found it was freezing inside. It had 8mm micro bore on oil CH.

We called a plumber and had them repipe the whole house and put in a closed system, and change all the rads. Kept same boiler.

The next winter was a revelation. Radiators now getting decent heat. The old pipes were throttling any heat , and just weren’t big enough. Along with crud it was closer to 2mm inside, and just couldn’t be cleaned.

I know it doesn’t answer your specific question, but I’d be losing the 8mm no matter what.

[ChocolateFrog]

gmaz said:

I've just had a survey from Octopus and they insisted on at least 15mm CH piping, so I think the microbore will need to be changed if you get an ASHP.

I also had existing 22mm piping from the gas boiler, but the surveyor said that would need to be changed to 28mm between the ASHP and unvented cylinder.

I'd highly recommend Octopus for the HP survey, they charge £200 (refundable if you sign up for the install) but it is a very comprehensive and detailed job.

If you want £100 off, email me for a referral code.

https://octopus.energy/order/heat-pump/

That's interesting, my 10mm was fine when they surveyed my house.

[PT1984]

thepritch said:

We moved into a granite cottage in Scotland in the winter. Soon found it was freezing inside. It had 8mm micro bore on oil CH.

We called a plumber and had them repipe the whole house and put in a closed system, and change all the rads. Kept same boiler.

The next winter was a revelation. Radiators now getting decent heat. The old pipes were throttling any heat , and just weren’t big enough. Along with crud it was closer to 2mm inside, and just couldn’t be cleaned.

I know it doesn’t answer your specific question, but I’d be losing the 8mm no matter what.

That’s just it. Boiler or ASHP. To ensure you can run low flow temps it needs doing.