32mm/28mm/22mm pipe runs ?

[Post and beam]

My proposed ASHP install is 12 metre run of 32mm from outside to under the stairs where the UFH manifold is. Then 16 metres of 22mm upstairs to the UVC.  7kw Vaillant Arotherm by the way.  Installers are saying the mismatch is an issue and the Vaillant needs 28mm anyway.  Do i have an issue ?

[Nickfromwales]

  On 03/04/2025 at 15:10, Post and beam said:

My proposed ASHP install is 12 metre run of 32mm from outside to under the stairs where the UFH manifold is. Then 16 metres of 22mm upstairs to the UVC.  7kw Vaillant Arotherm by the way.  Installers are saying the mismatch is an issue and the Vaillant needs 28mm anyway.  Do i have an issue ?

Expand  

Let them fit the 28mm throughout, as even a 300L cylinder has 1” BSP to 28mm connections so why not use them and have full use of the coil? It’ll perform better so where’s the harm. 
 

If it’s a smaller cylinder with factory 3/4” / 22mm connections then I’d challenge. 

[Post and beam]

The 32mm runs under the house and up though the block and beam to the manifold under the stairs. This is a 'fixture' now. Do you mean replace the 22mm from manifold to UVC  with 28mm Nick. Keith

[JohnMo]

  On 03/04/2025 at 15:10, Post and beam said:

12 metre run of 32mm from outside to under the stairs where the UFH manifold is. Then 16 metres of 22mm upstairs to the UVC

Expand  

Suspect your 22mm will cause pump to run out of head for satisfactory flow to cylinder. Which would then need an additional pump for cylinder heating.

[Post and beam]

Looks like i am running some 28mm then.

[Nickfromwales]

  On 03/04/2025 at 15:55, Post and beam said:

Looks like i am running some 28mm then.

Expand  

Yup. lol. One of those “measure twice” moments. 😜. Could be worse, so not the end of the world 😊