It’s altogether adequate to accept a high-efficiency boiler installed with one pipe. Just cast through the pages of any high-efficiency boiler accession chiral and you’ll acquisition the answer. I’m blogging about this because I’ve had abounding homeowners ask me about this.
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And now the blow of the story.
High-efficiency furnaces appear with two pipes; one aqueduct brings agitation air anon into the boiler and mixes it with fuel. The added aqueduct exhausts the agitation gases anon to the outdoors. Both of these pipes are directed to the outdoors at about 95% of the furnaces that I audit in Minnesota. In these systems, the boiler obtains all of its agitation air anon from the outdoors and exhausts the agitation byproducts anon to the outdoors. A two-pipe arrangement like this is alleged a direct-vent appliance.
I generally apprehend the agreement “direct-vent” and “sidewall-vent” confused. The 2015 Minnesota Ammunition Gas Code analogue of a absolute aperture apparatus is “Appliances that are complete and installed so that all air for agitation is acquired from the alfresco atmosphere and all flue gases are absolved to the alfresco atmosphere.” In added words, a two-pipe system. A one-pipe arrangement can be sidewall-vented, but will never be a absolute vent.
Side note: a concentric aperture looks like a one-pipe system, but it’s absolutely one aqueduct central of another. This is still a two-pipe system.
A two-pipe arrangement is bigger because the boiler won’t accept to use acrimonious calm air for combustion. There’s no crumbling of conditioned calm air.
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Another account to a two-pipe arrangement is added adaptability in the installation. Back the boiler gets its agitation air from the outdoors, you don’t accept to anguish about antagonism from the added calm appliances. You know, like that acquisitive kitchen bankrupt fan, or that blah accustomed abstract baptize heater. I affected on this in my blog column about architecture air and the 300 cfm myth. Also, you get the advantage to install absolute aperture accessories in places that you couldn’t otherwise; see area 303.3 of the MN Ammunition Gas Code for details.
There’s no botheration with a one-pipe system, but the rules for discharge are different. I’ve apprehend dozens, maybe hundreds of high-efficiency boiler accession manuals. Every distinct one of them had instructions for a absolute aperture and non-direct aperture installation. The diagram beneath from Goodman shows the altered discharge requirements for non-direct aperture and absolute vent.
So what do we say about one-pipe or non-direct aperture arrangement back we audit them? Nothing. We analysis to accomplish abiding that they’re appropriately installed, and that’s about all. Quite frankly, there’s beneath to go amiss with a one-pipe system. The alone affair that I consistently appear beyond is a agitation air assimilation that addition could accidentally set article on top of and block, like the one apparent below.
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The simple fix is to chase the manufacturer’s accession instructions. Put a aqueduct on there and add an elbow. Easy.
Author: Reuben Saltzman, Structure Tech Home Inspections
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