boiler vent size problem

I have a dispute between my plumber and the inspector and I'm hoping someone here can help out.

I have a WM CGI-5 propane direct vent boiler that was planned to be a direct vent however my plumber determined that for whatever reason he would connect it to the chimney as the old oil furnace was.

The vent is 3" stainless that travels 2 ft vertically and then through a 90 deg elbow into the old masonry pipe the boiler used which is a 6" opening that he has sealed with some kind of mortar.

The plumbing inspector is concerned with this and in the Weil Mclain installation manual - its clearly states for chimney venting a 5" pipe is required. I assume this is a negative pressure scenario.

However the plumber claims that as this is a positive pressure vent the 3" vent is correct - the WM manual just doesn't cover direct vent into a chimney. Who is correct?? Help please.

You go by what the manufacturer says in all cases. Weil McLain wants 5" here and that's what it needs to be.

Thanks nhmaster - my current vent is stainless steel - can I use galvanised to replace it - the WM manual does not specify this.

Also here is a pic of the vent and chimney connection.

Any advice/comments welcome.

Can you post more pics of the mechanical room. I am just grasping hydronics and I have this thing for mechanical rooms.

sure - its not too pretty...

So the boiler is not supplying heat for DHW¿ I see one pump but where is the secondary/system pump¿ What types of controls are you using¿

there is a propane HWH to the right - the boiler feeds the 2 baseboard zones with zone valves. This is controlled by the thermostat. Thermostat opens - this opens the zone valve and turns on the red circulator. I also have a zone with Onix tube radiant flooring. I'll probably add a circulator to this zone.

vent

Check with W/M to see if the 5" is a minimum size, not an absolute.

thanks HJ - do you know if I can use Galv vent pipe for a boiler?

Of course you can use galvinized pipe for venting a boiler...it will not last as long as stainless, but its a good investment none the less.

They also make 4" Plastic pipe for venting which I've seen used on some of the IBC boilers we install. Its just rated for a high temperature.

When it comes to installation of something like a boiler, you MUST adhere to the manufacturer's instructions. If they say SS, then you must use SS. If they give you options, as long as you use one of them, you're okay. You CANNOT make assumptions here. If it isn't stated in their manual, and you have a question, the best answer is to call their tech support number. The condensate of some boilers can be so acidic that it will quickly leach the cement out of mortar joints, degrade a chimney, and eat right through anything but stainless steel, and even then there have been problems with the use of the wrong alloy.

Just spoke to WM tech services - in this circumstance - venting into the chimney - I can use a single wall Galv pipe - 5" .

OK - problem resolved

Thanks for all the advice guys