Running MDPE up to loft?

[Romford_Pele]

Hi, I’m replacing my old lead mains pipe with a new 25mm MDPE pipe, which Thames Water are kindly helping with free of charge.

I had planned to terminate the MDPE pipe under my stairs, switch to 22mm and then run through the rest of my house. My new hot water cylinder and boiler are in my loft on the third floor, about 10m above ground level.

I’m concerned about flow and pressure. It’s currently pretty good, but 10m = 1 bar loss, which ain’t great.

I hadn’t realised this until today, but you can buy double check valves and stopcocks for 25mm mdpe pipe, so I don’t need to switch to 22mm under the stairs after all. Im now thinking that I could run the 25mm pipe all the way up to the loft, using the black version of the pipe, before teeing off for the cylinder hot/cold.

Similarly, I can tee off for the kitchen with an mdpe tee and then reduce down after.

By my calculations 25mm pipe offers a 29% flow improvement over 22mm, so this might offset the loss of pressure with the height of the cylinder…?

Does anyone know of any good reason why this would be a bad idea? I’ve got the space for the larger MDPE fittings.

Thanks in advance for your help

Gus

 

[oldbuffer]

1. I suspect your calculation is based on the outside diameter of the pipes.
2. Recalculated on the inside diameter suggests 22 mm copper is 2% narrower than 25 mm MDPE.
3. The figure in 2. above does not allow for any inserts required in the MDPE. I would suggest that if inserts are required (depending on fittings used) 22 mm copper pipe would offer better flow for a given pressure.
4. 22 mm copper tube has a wall thickness of 0.9 mm, so an internal diameter of (22 - (2 x 0.9)) = 20.2 mm
5. 25 mm MDPE pipe has a wall thickness of 2.3 mm, so an internal diameter of (25 -(2 x 2.3)) = 20.4 mm

 

[Romford_Pele]

Thanks for this. I hadn’t factored in wall thickness