Replacing Powermax 155

[ACOperson]

Have got a customer looking to replace a Range Powermax 155 (installed in new build property - 2000) with a Vaillant 37kw combi.

It is going to be sited away from where the current unit is (cupboard in the middle of the house), and I was wondering if anyone had any thoughts on the DHW pipework situation?

Currently the Powermax has a 22mm outlet for DHW, splitting into 3 x 15mm outlets (2 bathrooms & kitchen) under the floor. They are looking to install the new boiler in the kitchen and tap onto the 15mm DHW pipework under the sink. I've got doubts over the 15mm pipework's capability to provide the flowrate we need to run potentially 2 showers off.

Any thoughts welcomed - cheers

 

[gas4you]

As my understanding of a powermax is that it is more like a thermal store combi boiler I think the customer will not get the same hot water performance from the 837, due to any standard combi only wants to supply one tap at a time. If they have the space I would recommend the 937 storage combi. This has a 15 litre store for hot water behind the 837 combi, so will give good flow rate and if resevoir is depleted you still have a 15l/min combi flow rate

 

[ACOperson]

Dont think they have room for this new Vaillant in their kitchen, it projects about 0.5m out!

Also, a 15 litre store is not much, I think that would be just about enough for 1 minutes use of one of their showers!

Anyone got any idea of the volume of water a 15mm pipe can pass in 1 minute? Their working pressure is massively high, over 3 bar.

 

[simond]

The passage of water through the 15mm pipe will depend on the length, no of bends etc.

The ability of the PowerMax will be limited by the incoming water supply, have you measured the flow rate?

The ecoTEC 937 (like the old aquaPLUS it is based on) uses the 15 litre store to mix in with the HW created in the 37Kw combi to deliver the higher flow rate listed. It will deliver 20l/m for the first 200 litres, your shower observation is ill founded.

If you want a similar replacement for the Powermax you could also look at the Viessmann 333. This has a much larger unvented store inside, but similar performance figures to the Vaillant. The Viessmann is not a cheap boiler, but represents the current state of the art in hybrid combis....in my opinion