steam boilers - can they be direct vented?

allenh

Is the additional hardware on the boiler or outside the building?

Kevin_in_Denver_2

Sealed Mechanical room

The two main goals of direct venting are:



1.  Protect against CO

2.  Eliminate cold drafts due to incoming combustion air and the stack effect through the flue.



If you pretend the mechanical room is outside, you'll have "sealed combustion", which is a synonym for direct venting.



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Worried about frozen pipes?  Definitely insulate all the pipes in the

room, especially that incoming cold water supply in the path of that

combustion air.  The overall temperature in the room won't drop below

freezing, however, due to losses from the boiler and flue pipe.  When

the makeup air is below freezing, the boiler is operating more.



Watch out for freezing if you turn down the thermostat too much for a long period.

Kevin_in_Denver_2

Direct Vent Steam Boiler

I haven't heard of a direct vent steam boiler, but I think Steamhead has mentioned putting an optional combustion air "snorkel" on steam boilers.  That gets you half way to direct venting, and eliminates the freezing problem I mentioned.What are you trying to accomplish?

Steamhead

Pretty much any boiler

can be fitted with a powered sidewall venter, and can have combustion air brought to its general area from outdoors, as long as Codes and instructions are followed to the letter. But there are two things to think about when considering this:



1- Is there a proper and safe place to exhaust the flue gases? Codes vary somewhat and so do inspectors, but in general you're looking for a spot where the pipe can exit the building that's 4 feet from windows or doors (or other penetrations of whatever type), at least a foot above the highest recorded snow accumulation in your area (for obvious reasons), and not too close to an inside corner of the wall. And if you're exhausting over a publicly accessible walkway, the height requirement increases to 7 feet. This is a tall order in many existing buildings.



2- Direct-vent and power-vent equipment is mechanical and WILL require service. When properly installed, if such equipment breaks down it will stop the burner until it's fixed. This makes me really appreciate the traditional chimney, which has no moving parts.



Now if you're going this route, and the boiler will be gas-fired, it's best to choose a boiler with a power burner that can be fitted with an "air boot" to bring in outside air straight to the burner. Even residential boilers can do this if equipped with the Carlin EZ-Gas burner. If you're burning oil, you're OK since all oil burners are power burners. But you have to be very careful when setting up a power- or direct-vented oil burner or it will soot up the outside wall of the building.



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