Viessmann 222f advice

We're looking to have one of these installed and have had a couple of quotes.

One plumber suggests using 22mm from the DHW outlet (stepped up) as this will help with the flow when using more than one outlet.

The other says that as the boiler has a 15mm outlet that 15mm will be fine and that 22mm would make it take longer for hot water to reach the outlets!

We're very fortunate that our main bathroom and ensuite are next to each other and the runs from the boiler would be about 3.5m in length.

Water main will be 32mm MDPE, 28mm stop cock, 22mm upto the PRV and into the boiler.

Which quote would you go with?

That unit is capable of quite a good flow rate.

But without knowing whet the dynamic flow rate from your supply will be or even your required maximum flow rate its not really possible to come to any conclusion.

Both installers should be able to quote for both pipe sizes.

Tony

Thanks for the reply Tony, the dynamic flow from my old 1/2" main is 32lpm at 1.5bar

The second engineer was willing to install 22mm if I wanted.

How much water does 3.5m of 22mm pipe hold? From that I can work out how long it would take to get hot water out of a basin mixer and see if that would bother me.

Viessmann state a peak flow of 20lpm giving 200 litres in the first 10 minutes, that's at 60 degrees!

I think this should handle 2 showers at the same time when it's blended down which makes me lean towards the 22mm