High Efficiency Furnace Intake/Exhaust Setup

Shane Pouch · 06-27-2007, 07:46 AM

Hello to all,

Have not seen an intake/exhaust setup like this before. It's a Nordyne (Philco) G6RC 080C-12B model (90%). I normally see 2 pipes routed to the exterior. Can't seem to put my hands on any documentation that would either confirm or deny the arrangement. I snooped around the basement trying to find the owner's manual - no luck!

Is it okay?

Thanks,

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**Nick Ostrowski** · 06-27-2007, 08:10 AM

Shane, this configuration is generally just laziness on the part of the installer. They've already routed the exhaust line to the exterior. Why not route the combustion air intake line there as well?

It's not ideal but to the best of my knowledge, still allowable.

Shane Pouch · 06-27-2007, 08:47 AM

Nick, Yeah, I was leaning toward it is probably okay. It's drawing from an unfinished basement just like a low- or mid-efficiency furnace would be.

Just wasn't sure.

Shane Pouch · 06-27-2007, 10:04 AM

Found the installation guide, and have attached the pages regarding the venting.

One pipe install is acceptable.

Frank Kunselman · 06-27-2007, 10:17 AM

Shane, You would be surprised how many installers never read the manual. You'll see one one of these days without the requied elbow.

I've laid my inspection book on many a furnaces like this without the elbow, in front of the mech installer and said "I've just killed the unit by cutting off the combustion air." Only then did they get the point and follow the manual.

Good luck.

**Bob Harper** · 06-28-2007, 06:45 PM

I had two similar units side by side in a house with a smoking fireplace. When either kicked in, the Fp would smoke like crazy. As I remember it, there was about -15 Pascals WRT the basement while only about -5 to 6 WRT outdoors. While in the basement with one unit running, I held my CO analyzer near it and it starting climbing fast. It was backdrafting the unit 3 feet away. Not only that, it was backdrafting the DHW heater 6 feet away, which was B-vented. The Bldr's Super almost passed out! He thanked me and followed my recommendations on correcting the house and the fireplace then worked. The extra 12 feet of chimney they added on had no effect. As you make chimneys taller but they are now hanging in the breeze, it cools the stack so very quickly you hit a point of diminishing returns unless they also extend the chase to protect the pipe from the wind.

I've seen these intake snorkels sucking in fumes from nearby paint cans, laundry chemical fumes and dryer lint. This arrangement really ought to be banned. Should pull from outdoors 100%. At least it is usually fairly easy and inexpensive to correct.

**Nick Ostrowski** · 06-28-2007, 06:58 PM

Bob, I had heard that bleach fumes from a nearby laundry area can prematurely rust out a furnace. True?

**Bob Harper** · 06-28-2007, 07:20 PM

That's a very popular rumor floating around. However, there seems to be a dearth of scientific evidence to support it. Caoihim Connel (sp?), our Industrial Hygienist online has stated this is utter bunk. He said in essence, the Chlorine would need to be in an ionized form but it doesn't so the theory is BS in his book. He's a real smart cookie so I'm hoping he'll chimne in a correct me or state it more clearly.

Now, if you have chlorinated compounds being oxidized, I'd be interested to see the chemical reaction written out. I have always read and been told gas appliances form HCl or stomach acid while oil burners form H2SO4 or sulfuric acid, which is battery acid. Both supposedly can make some nitric acid at high temps along with some NOx but not at normal temps. There again the PEL for NOx is trace level ( I believe parts per Billion).

Nick, I know a lot of mfrs. state in their manuals to keep laundry equipment and household chemicals away from combustion appliances. May just be an unproven theory that has become urban legend.

**DavidR** · 06-30-2007, 09:46 AM

Originally Posted by Bob Harper

. May just be an unproven theory that has become urban legend.

I tend to go with the urban legend side of this.

If equipment manufacturers would just install real post purge circuits in their furnaces that ran anywhere from 3-5 minutes after the burner shut down the rusting issues in induced draft equipment would almost disappear.

The rest of the cases in induced draft equipment would normally be taken care of by firing that equipment at it's proper rate.

There are some other factors that go along with atmospheric equipment & those pesky drafthoods.