Today’s case study looks at an interesting house near Leatherhead, Surrey, UK.

Van in a state of readiness to consume old iron commercial boiler

Outwardly, it looks like a chalet bungalow, but at the some point in the past, a massive cellar was excavated underneath with a swimming pool, games room and boiler room.

Bit dark in the boiler room – flue shown passing through trench under footings

This was some years ago and the present owner has no need for the swimming pool, which together with the associated boiler/plant room, was at the end of its economic life.

The pool and house was heated by a large iron open flued commercial boiler with a pressure jet burner.  There was masses of wiring in the cellar area, with relays and large panel mounted wiring boxes.  Other Gas Registered technicians had apparently been over to do quotes and had run away, fazed by the complex electricals and the size of the boiler, which made it borderline within normal domestic gas qualifications.

However, we had a few things in our favour.  We are qualified in commercial gas, and also hold electrical qualifications, so it didn’t look quite so bad.  Once one had taken the pool heating out of the equation, rather than just blindly assume that the 60Kw boiler had been sized correctly, we did a heat calculation on the property – including the areas to be refurbished – and found that a 37kw boiler would be more than adequate for the task.

New Vaillant system boiler, ecoTEC MkII 637 model

Fitting a boiler in a basement, especially with thick concrete walls, makes getting the flue out somewhat challenging.  The original cast iron boiler had been fitted with what can only be described as a ‘moody’ flue, which run horizontally in the boiler room, and then once outside, straight up the exterior wall to a terminal at gutter level.

We specified a Vaillant ecoTEC MK11 637 boiler, fitted with their weather compensation system.  It was connected to an existing open vented hot water cylinder – although our customer plans to upgrade in the future to a Vaillant uniSTOR unvented…

The flue system was difficult to achieve because we had to run it through an underground duct and then vertically outside.  We wanted to end up with a vertical termination of combustion products, so we used Vaillant’s variable termination kit and constructed a small external enclosure in brick for the flue outlet from downstairs.  Concentric flue joints have to be inspectable after installation under new Gas Safe Register rules, so adequate provision was made for this, by making the slab on the external box simply removeable.

New flue arrangements. Weather sensor installation visible behind.

The new Vaillant controller was fitted in the hallway, and the house heated up nicely.

Unfortunately, the boiler room lighting was not working at the start, so limited photos of the ‘before’.  The customer bought a nice high frequency flourescent fitting which I fitted, so the ‘after’ photos are a bit bit clearer!

Nearly finished, just some final bits of swimming pool pipe to remove at this point