New boiler options - what to buy

[Alex Theochari]

I have been looking at replacing an ageing combination boiler for a while.

I wanted to move to a system boiler with a twin coil cylinder. I have decided to get a joule cylinder, partly because I got one for my parents with no issues and partly because they are one of only a handful of manufacturers that make a dedicated horizontal cylinder.

Back to the boiler question...

My short list is four boilers, two from Viessmann and two from Atag.

My preference is a Viessmann Vitodens 300 however I am not sure if it is best suited for the requirement and if it does offer an added advantage.

So, the setup is to (if cost effective and possible) replace the radiators with aluminium ones, have underfloor heating in the new kitchen/dining area (6.5m x 3.2m and 3.2m high) and a bathroom (3.5m x 2.6m x 2.4m). Possibly install solar thermal for water (however as long as I have the setup now I can always do this next year).

So, the choices of boilers are:

Viessmann Vitodens 300-W 35KW
Viessmann Vitodens 200-W 35KW

Atag A320S System boiler
Atag Q38S System boiler

The reason I leaned towards the Vitodens 300 is that it modulates really low and for underfloor heating this is a positive. However I am not sure if that adds such a benefit or not.