will a gas balanced flue compromise air tightness

[lakelandfolk]

Hi All,

Hoping to get close to passivhaus standard with our proposed build but wondering if the flue from a small gas system boiler will compromise the air tightness. I know a balanced flu draws air in from the outside via the outer tube into the burning chamber but is that chamber sealed to prevent air being drawn from within the building?

[Nickfromwales]

A new boiler will be called an RS ( room sealed ) appliance, unless you choose a balanced flue which I presume you wouldn't want. 

The combustion chamber, air in / fumes out ) is all entirely sealed to the outside atmosphere via the coaxial flue.   

Airtightness will only be compromised by making the penetration for the flue. I'll post some pics of the last MBC build where I had the same thing to do. 

 

[Nickfromwales]

FYI balanced flue appliances draw air from the room and use convection or fans to blow the fumes out to atmosphere. 

[ProDave]

1 hour ago, Nickfromwales said:

FYI balanced flue appliances draw air from the room and use convection or fans to blow the fumes out to atmosphere.

I thought that described an open or conventional flue?  I always understood "balanced" flues drew combustion air in from the outside and expelled combustion products outside. Often with two flue pipes adjacent in a rectangular housing, rather than coaxial.
 

[tonyshouse]

In theory balanced flues should not influence air tightness 

 

in practice there are nearly always draughts happening around the flue pipe 

[Nickfromwales]

2 hours ago, ProDave said:

I thought that described an open or conventional flue?  I always understood "balanced" flues drew combustion air in from the outside and expelled combustion products outside. Often with two flue pipes adjacent in a rectangular housing, rather than coaxial.
 

You're right, apologies. It's open flue that's dependant on adventitious air from within the dwelling  

Balanced will rely upon the seals of the combustion / burner chamber for air tightness but should be ok for PH as its not allowed to leak products of combustion into the dwelling aka air / gas tight. 

Most system boilers would be RS tbh, so choosing well should mitigate most of the concern. The issue of the air tightness of the penetration for the flue, from inside to out, still remains the key to keeping the house 'sealed'. 

 

[Auchlossen]

ah so what is the collected wisdom on the best brand of RS gas boiler?

[Nickfromwales]

Intergas gets a good mention here, but as I've stated here, and on EB, I'm a Baxi or Vaillant man myself. I've been around boilers for over 20 years and have based my findings around breakdowns / failures, longevity, dhw production and price. 

Viessmann are over priced IMHO, and likewise for WB. They both survive off their pedigree and following IMO, with WB being just synonymous with British Gas.  

Vaillant are very robust, well built and reliable machines, which seem to be free from any early / mid term failures. Baxi are my instant second choice below them, should budget be a constraint. The Baxis are a little cheaper but are also very, very reliable too and have equally good dhw flow rates. 

The vaillant 938 ERP is a heat-store combi with the equivalent dhw output of a small UVC. They're incredibly good at supplying hot water and don't suffer any delay in producing dhw, as regular combis do. If you want to be able to shower whilst other hot / cold outlets are used elsewhere in the house then this is the one to have   

[lakelandfolk]

Thanks for that info, I will put a Vailliant Ecotec Plus 612 on my short list.

[Nickfromwales]

[Trw144]

45 minutes ago, lakelandfolk said:

Thanks for that info, I will put a Vailliant Ecotec Plus 612 on my short list.

 

That's what I had in the last house and have opted for the same again....

[Nickfromwales]

Cracking machine .