Condensing System Boiler and heating/DHW

ian123

Hi

I got a condensing system boiler (vitodens 050-w 25kw) to replace an older baxi system boiler. I understand that Condensing boilers need to operate around to 50C mark to enable most efficient performance (ie allow heat transfer from flue). However, 50c is not the recommended temp for DHW (60C+ is preferred). The 050-w appears to have both heating and DHW connections/capability - in my case out of the 5 valves for connecting to heating/DHW, the two valves related to DHW are not connected.

Given the need for 60C + for DHW, it seems to be me that i have to run this boiler at 60C (for DHW) and as a result I will NOT be able to get the efficiency promised from the boiler (that would be achieved around ~50c).

In terms of house construction - my house has 2 heating zone and DHW - built in 2004 - would it be normal to have common pipe work for both heating and DHW - or would it be traditional to have a dedicated pipe circuit for DHW separate to the heating system? - i am just wondering if the vitodens installers took a short cut or not.

thanks

Lenar3556

I am not familiar with that particular boiler, but most likely;

50 degrees is the optimum return temperature to facilitate condensing taking place. The flow temperature that you set on the boiler should usually be at approx 70degrees. Your installer should balance the system to provide the correct return temperate when commissioning the boiler.

Yes, the cylinder should be kept at 60degrees.

Many gas boilers have a facility to provide different flow temperatures to hot water and radiator circuits. In some cases it can be useful. Would this be typical of a house built in 2004 - not in my experience.

Wearb

A condensing boiler will operate quite well above optimal return temperatures. It still manages to extract a lot of the latent heat from the flue gases. This can be easily observed in the much lower flue gas temperature compared to a standard boiler.

shane b

Its a Veissmann Vitodens boiler and comes with a 10 year parts warranty i believe. Traditionally boilers only have 2 pipe connections its the 1 flow and return pipe for heating and hot water.

The boiler in my 2004 house packed in after 17 years and as my house is plumbed for hot water priority, the Veismann Vitodens is one of the few boilers with 2 flows and 2 returns capable of this configuration. The plumbers i contacted mentioned that it being plumbed this way would'nt be the norm in Ireland.

ian123

Thanks that diagram is what I was expecting. Seems to be a waste not having the ability to separate DHW that reqs a higher temp from the radiators that don't need as high. I have a thought of just using night time off peak ~7c/unit electric to heat water overnight rather than use gas (at 8.5c/unit)