forced air system 'missing' intake air pipe

[Ernie Simpson]

I inspected in new condo in an old three decker today. The unit had a new forced hot air, gas-fired system. Gas off, system not run during the inspection. The furnace had a standard direct vent PVC exhaust vent out the sidewall. But, the system had no direct air intact to the enclosed combustion chamber. The hole on the top of this (see photo) was just an open hole. The closet had louvered doors to separate the closet where the heating system was located from the living space. Totally bogus (sorry for the lack of technical language) in my opinion, but just to be sure, I would appreciate feedback/confirmation on this. This needs a proper direct air intake, I would assume. Correct? I recommended also that they make sure the local heating inspector sign off on this installation.

(Note: Water stains on top of furnace, I believe caused by water running down from still unsealed roof pass-through for AC piping).

Image Insert:

232.36 KB

[Neal Lewis]

Ernie, read the manufacturer's instructions to find out for sure. i have a few installation manuals for Cat IV furnaces, and they all basically say the same thing.

Furnace is certified to be installed with one of three possible intake/vent configurations.

1. Two pipe with a sealed combustion intake/vent systm using outdoor combustion air.

2. Single pipe vent system using combustion air from the area surrounding the furnace.

2. Two pipe intake/vent system using combustion air from the a ventilated attic space and a vent to the outside.

Some municipal inspectors might require a 90 degree bend on the intake to prevent something from being placed over the opening.

[hausdok]

Neal is right,

I'd guess that, since there is no intake pipe and the door to that area is louvered, that the area around the furnace meets the manufacturer's requirements for adequate combustion air without an exterior air source. However, it's been my experience that a lot of the time these furnace guys don't take into account things like gas clothes dryers and gas water heaters that are operating in close proximity to these devices and which impact combustion air requirements.

That looks like the manual for the furnace on the right side; did you pull it out, open it up and read the combustion air requirements?

Also, sometimes they'll have louvered doors opening into a little room that, when the door to that room is closed, provides far far less combustion air than is required.

You've got to look at the whole picture. If there are other gas appliances in close proximity, I generally estimate the volume of the adjacent space, total up the BTU/HR requirement for all appliances, divide that by a thousand, and then multiply it by 50 to see if the it meets the basic rule-of-thumb combustion air requirement for gas appliances. If not, and I can't confirm with the manual that the existing space is adequate despite being less than that required by the rule of thumb, I write it up to be checked out by an HVAC pro.

ONE TEAM - ONE FIGHT!!!

Mike

[Jim Katen]

Even if the combustion air is adequate, the opening should be extended to point down and be covered with rat wire.

- Jim Katen, Oregon

[inspector57]

You did note the lack of condensate drains on the A/C coil, right?

[jon_ran]

Some manufacturers allow it, as other have said. But to get the highest efficiency, the unit must pull air from the outside. Otherwise you are pulling "conditioned" air from the home and blowing it outside, which then causes unconditioned air to be pulled in around windows, doors, outlet boxes, etc.

[kurt]

Originally posted by Jim Katen

Even if the combustion air is adequate, the opening should be extended to point down and be covered with rat wire.

- Jim Katen, Oregon

The one's I see have a metal grate that fits in the hole.

[Ernie Simpson]

Thanks for all of the replies. While I understand that there is nothing (except see below) from keeping the furnace from working properly with this configuration (assuming that the allowable air for combustion is sufficient), one concern I would have is this; what if someone places the instructions (or some other solid object over the open hole that is used to supply the fresh air for combustion. That would not be good... (CO production, unit most likely kicking off, etc.). Also, they're going to have a little kid at this unit. What if she drops a little toy into the open hole.

One poster (sorry, didn't record who) noted there should be a grate over the hole. This would at least keep foreign objects out of the burner compartment. Still, I think this should have a vent to the exterior - or at least a vent pipe that can't be covered with a solid object.

(Also, the AC installation was not fully installed to date so I assume they will still be installing the condensate drain. I offered to do a later inspection so this can be checked for then, if they take me up on it).

[hausdok]

Hi,

That's fine, except recommending that they extend an intake pipe to the outside after they've already got things on the interior configured the way the manufacturer requires for a furnace pulling air from the interior is going to make you look a little bit pedantic and goofy and could damage your credibility. If they've installed it within parameters required by the manufacturer and the code, telling them now to install an exterior intake pipe is just spoiling for trouble.

You have to learn to pick your battles in this business and I don't see that as a battle to be fought; at least not in this circumstance. Yeah, as Kurt and Jim say, something to keep critters or objects from fallling into the intake pipe would be good, but I wouldn't be worrying about somone covering up that hole. You can't anticipate every action that someone else is going to do around that furnace, nor should you. Besides, if that intake hole gets blocked, the furnace should shut down - if it doesn't, it's not on you, it's on the manufacturer.

Sorry if this came off as grouchy, but it's been a sucky day.

ONE TEAM - ONE FIGHT!!!

Mike

[Rob Amaral]

Ernie: I seem to recall someone mentioning that vapors from 'laundry use' (chemicals, etc) in a basement 'might' adversely affect this type of furnace (extra corrosion). That seemed to also be one of the reasons to get the comb.air from outside (besides other obvious reasons). I too have seen the mfgr specs OK-ing this. When in doubt, read the manual or go to the mfgr's website.

[Jim Morrison]

Hey Guys,

Ernie needs no introduction in New England, but some of you (from less civilized parts of the country [] )may not know him. He's been doing inspections since around the time men stopped living in caves and is a great guy to boot. He's got a headful of great knowledge to share, and we're lucky to have him.

[ozofprev]

Then welcome Ernie! We hope to hear and learn much from you. This forum has some of the best - and egos don't get too ornery.

[hausdok]

Yes, by all means, welcome Ernie; we need more old hands hanging out around here from all parts of the country 'cuz some of us aren't familiar with systems commonly used in other parts of the country. I'll bet Earnie can teach us northwesterners a thing or two about boilers and steam heating systems which are scarce as hens' teeth around here.

By the way, Jimmy, when exactly did men stop living in caves? I must have missed the memo. []

ONE TEAM - ONE FIGHT!!!

Mike

[Jim Morrison]

Dear Knuckle-dragger,

We left caves (and started walking upright as well) years ago, but Yung says you've got to stay in the cave. Sorry.

[hausdok]

You could've fooled me:

http://findarticles.com/p/articles/mi_m ... i_78783509

http://www.encyclopedia.com/doc/1G1-19385242.html

http://www.answersingenesis.org/creatio ... /malta.asp

http://www.showcaves.com/english/au/reg ... rPedy.html

http://www.showcaves.com/english/de/mis ... stein.html

OT - OF!!!

M.

[Mogollon]

After looking at the picture, WHERE IS THE AC condensate drain line??? Looks like it is missing too.

[hausdok]

Mogollon,

If you read post #8 of this thread, you'll see where he says that as of the date of the inspection the AC install hadn't yet been completed.

OT - OF!!!

M.