Thread: CatIV furnace venting near compressor

Do any of you HVAC guys see a concern with this installation. It's a concentric vent for the condensing furnace terminating next to an AC unit.

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I don't know about that answer, but here is what else I see:
- no proper working space at service access to condenser unit
- air flow to condenser unit likely will interfere with air flow from vent to right of condenser unit, by the way, what is that vent for?
- condenser unit should be on at least a 3" high stand, sleepers, or something, probably even higher - depending on your snow loading depth
- is that goose neck PVC sealed around the refrigerant lines?
- is that condenser unit anchored down, and to what?
- The disconnect enclosure mounted to a single conduit like that needs a second conduit mount or some other bracket mounting (to keep the disconnect from being able to be turned on the conduit mounting)

Hi Jerry,

I don't know about that answer, but here is what else I see:
- no proper working space at service access to condenser unit

- air flow to condenser unit likely will interfere with air flow from vent to right of condenser unit, by the way, what is that vent for?

Bathroom exhaust I believe. THis is a mixed- use building with a combo of store fronts and condo units. I was just doing an interior only condo inspection. Is there some literature I can look at that that would ID this as an improper installation?

- condenser unit should be on at least a 3" high stand, sleepers, or something, probably even higher - depending on your snow loading depth

Snow loading depth. What's that I think we had maybe a few inches of snow in December-- only time this year. Here's another picture showing that the units are in fact up off of the roof.
- is that goose neck PVC sealed around the refrigerant lines?

Not yet-- see new pic.
- is that condenser unit anchored down, and to what?

Will you point me towards that requirement please.
- The disconnect enclosure mounted to a single conduit like that needs a second conduit mount or some other bracket mounting (to keep the disconnect from being able to be turned on the conduit mounting)
Will you point me towards that requirement as well? I don't like that "pedestal" type installation for another reason. The mounting holes are open in the back. Water can pour right in.

Originally Posted by Brandon Whitmore

Bathroom exhaust I believe. THis is a mixed- use building with a combo of store fronts and condo units. I was just doing an interior only condo inspection.

The IRC does not apply, the IBC, IMC, IPC, etc., apply instead.

Is there some literature I can look at that that would ID this as an improper installation?

That exhaust vent cap? Not sure, but they do not look like anything I've seen approved, but then the wind blows a bit where I am.

Snow loading depth. What's that I think we had maybe a few inches of snow in December-- only time this year. Here's another picture showing that the units are in fact up off of the roof.

Still needs to be above adjoining grade.

From the 2006 IMC.
- 304.9 Clearances from grade. Equipment and appliances installed at grade level shall be supported on a level concrete slab or other approved material extending above adjoining grade or shall be suspended a minimum of 6 inches (152 mm) above adjoining grade.

"Adjoining grade" in this case is the roof.

Jerry said: - is that condenser unit anchored down, and to what?

Will you point me towards that requirement please.

- 304.1 General. Equipment and appliances shall be installed as required by the terms of their approval, in accordance with the conditions of the listing, the manufacturer’s installation instructions and this code. Manufacturer’s installation instructions shall be available on the job site at the time of inspection.

The IBC will also require them to be anchored to resist the wind loading forces, and you guys get so strong winds too, as I understand.

The manufacturer will require it.

Jerry said: - The disconnect enclosure mounted to a single conduit like that needs a second conduit mount or some other bracket mounting (to keep the disconnect from being able to be turned on the conduit mounting)

Will you point me towards that requirement as well? I don't like that "pedestal" type installation for another reason. The mounting holes are open in the back. Water can pour right in.

From the 2008 NEC.
- 300.11 Securing and Supporting.
- - (B) Raceways Used as Means of Support. Raceways shall be used only as a means of support for other raceways, cables, or nonelectrical equipment under any of the following conditions:
- - - (1) Where the raceway or means of support is identified for the purpose
- - - (2) Where the raceway contains power supply conductors for electrically controlled equipment and is used to support Class 2 circuit conductors or cables that are solely for the purpose of connection to the equipment control circuits
- - - (3) Where the raceway is used to support boxes or conduit bodies in accordance with 314.23 or to support luminaires in accordance with 410.36(E)

Technically, the raceway should not be used to support that enclosure for the disconnect as that is not a box or conduit body, it is a cabinet, however, allowing for this variation and being supported on the raceway, you would then go to 314.23.

- 314.23 Supports.
- - (E) Raceway Supported Enclosure, Without Devices, Luminaires, or Lampholders. An enclosure that does not contain a device(s) other than splicing devices or support a luminaire(s), lampholder, or other equipment and is supported by entering raceways shall not exceed 1650 cm3 (100 in.3) in size. It shall have threaded entries or have hubs identified for the purpose. It shall be supported by two or more conduits threaded wrenchtight into the enclosure or hubs. Each conduit shall be secured within 900 mm (3 ft) of the enclosure, or within 450 mm (18 in.) of the enclosure if all conduit entries are on the same side.
- - - Exception: Rigid metal, intermediate metal, or rigid nonmetallic conduit or electrical metallic tubing shall be permitted to support a conduit body of any size, including a conduit body constructed with only one conduit entry, provided the trade size of the conduit body is not larger than the largest trade size of the conduit or electrical metallic tubing.
- - (F) Raceway-Supported Enclosures, with Devices, Luminaires, or Lampholders. An enclosure that contains a device(s), other than splicing devices, or supports a luminaire(s), lampholder, or other equipment and is supported by entering raceways shall not exceed 1650 cm3 (100 in.3) in size. It shall have threaded entries or have hubs identified for the purpose. It shall be supported by two or more conduits threaded wrenchtight into the enclosure or hubs. Each conduit shall be secured within 450 mm (18 in.) of the enclosure.
- - - (there are a long list of exceptions, none of which apply)

Thank you sir.

The IBC will also require them to be anchored to resist the wind loading forces, and you guys get so strong winds too, as I understand.

The manufacturer will require it.

I'll have to pull up the Oregon Mechanical Specialty Code (2004 version in this case), which I do not study. I try to stick to residential inspections as much as possible, but do the occasional condo, especially during slow times.

Thanks again.

air flow to condenser unit likely will interfere with air flow from vent to right of condenser unit

This was what I was questioning/ asking for info. on.

The airflow from the condenser should not affect the vent to the right but, the other way around. I seriously doubt that it affects it at all. As long as the condenser coil is not blocked the condenser fan will pull air thru it. the only concern is, do you want whatever comes out of that vent going thru the coil?

The original question was about the concentric vent. No it's not a problem with the condenser as when the unit is heating it's not cooling. But the concentric vent should be higher than the expected total snowfall for your area, it seems low.

Following up on rooftop mounting requirements, does anyone have a link to Carrier's:

"Application Guideline and Service Manual — Residential Split-System Air Conditioners and Heat Pumps" ?

The original question was about the concentric vent. No it's not a problem with the condenser as when the unit is heating it's not cooling

Hi David,

My concern is that there are byproducts of combustion (NOx for example) coming out of the concentric vent. During the right weather conditions such as inversion layers, winds,etc., the AC will be exposed to the exhaust. Maybe I'm over thinking this, but thought that premature corrosion or oxidation may occur. Since nobody is jumping on here saying "oh my gosh, that's a problem", I doubt it is.

I pulled this off of Google:

NO

x can make the body vulnerable to
respiratory infections, lung disease,
and possibly cancer. NOx contributes
to the brownish haze seen over
congested areas and to acid rain.
NOx easily dissolves in water and
forms acids which can cause metal
corrosion and fading/deterioration of

fabrics.

The more I think about it, the more I realize that it probably won't be a big issue. If it were, furnace manufacturers wouldn't still be using aluminum heat exchangers, would they?

Originally Posted by Brandon Whitmore

My concern is that there are byproducts of combustion (NOx for example) coming out of the concentric vent. During the right weather conditions such as inversion layers, winds,etc., the AC will be exposed to the exhaust. Maybe I'm over thinking this, but thought that premature corrosion or oxidation may occur.

My thinking too.

Since nobody is jumping on here saying "oh my gosh, that's a problem", I doubt it is.

That's not the conclusion I would jump to based on lack of input ... it is quite possible that ... none of us know ...

That's not the conclusion I would jump to based on lack of input ... it is quite possible that ... none of us know ...

True, but....... Based on the fact that manufacturers still use aluminum heat exchangers that are exposed to much more NOx, I'm having a hard time believing it will be a problem-- within the manufacturers warranty period that is

Originally Posted by Brandon Whitmore

True, but....... Based on the fact that manufacturers still use aluminum heat exchangers that are exposed to much more NOx,

Are they exposed to more combustion byproducts?

And is the same aluminum, of the same alloy, of the same thickness, of the same etc., used for both? The coil fins are very thin and flimsy as they are trying to give off heat to the air which flows over it and are not designed to be set over a high burn flame and heat like the heat exchanger is.

Looking at the second pic in addition to the first, a few questions.

What is the distance from the overhang of the eave at the roof scuttle to the mechanical and vent area, the distance from the half wall.

I believe I see a bvent cap at the third grouping to the right in the second photo, at a higher elevation. I wonder how domestic hot water is supplied to the condo units - are there individual fuel fired water heaters? Looks like the other groupings include two and/or three plumbing vents - assume this unit has a second aux vent nearby too. Kitchen have mechanical ventilation too?

What is the proximity/scale to the plumbing vent to the right?

I'd like to know the scale and identification of all the terminations - it appears this area is extremely crowded, and has a multitude of mechanical assisted venting and intakes in one small area which is an alcove of sorts encircling the condenser or heat pump. Is this an AC unit only or a heat pump?

Without a scale reference it is difficult to determine but it appears there is more than one clearance/pressure issue not just the condenser, especially with presence of fan assisted/mechanical venting so close to intakes, and clearances for the condenser operation as well as maintenance access personel room. Is that a servicing receptacle below the disconnect box? what's the height there?

Roofing membrane damage noted?

And, that condensate line needs a vermin shield

What is the distance from the overhang of the eave at the roof scuttle to the mechanical and vent area, the distance from the half wall.

Hi H.G.,

There is no roof scuttle. Access is via a permanent ladder on an exterior wall. In the second picture you can see skylights for the other units. My unit was the one with the sloped roof cover.

The distance to the half wall with the window in it was between 5.5 and 6', while the overhang extended about 3'. I no longer have the measurements, so this is based on memory.

I believe I see a bvent cap at the third grouping to the right in the second photo, at a higher elevation. I wonder how domestic hot water is supplied to the condo units - are there individual fuel fired water heaters? Looks like the other groupings include two and/or three plumbing vents - assume this unit has a second aux vent nearby too. Kitchen have mechanical ventilation too?

There are no B vents, at least not in the area directly above my condo. The condo units have individual unit electric water heaters and condensing gas furnaces.

There were 3 bathrooms in my unit, and a kitchen, all of which were vented to the exterior. The kitchen and 2 bathroom exhaust ducts vented through sidewalls with typical louvered vent covers showing on the exterior-- all painted shut of course. The 3rd bathroom exhaust, laundry room exhaust, and dryer duct all appeared to be vented onto the roof.

What is the proximity/scale to the plumbing vent to the right?

Unknown-- I didn't measure it. It wasn't close enough to the furnace vent to be an issue.

I'd like to know the scale and identification of all the terminations - it appears this area is extremely crowded, and has a multitude of mechanical assisted venting and intakes in one small area which is an alcove of sorts encircling the condenser or heat pump. Is this an AC unit only or a heat pump?

All I have is pictures-- no measurements. It was extremely crowded. It's just an AC unit, not a heat pump.

Without a scale reference it is difficult to determine but it appears there is more than one clearance/pressure issue not just the condenser, especially with presence of fan assisted/mechanical venting so close to intakes, and clearances for the condenser operation as well as maintenance access personel room.

What code references can you throw my way so that I can learn from all of this?

Is that a servicing receptacle below the disconnect box? what's the height there?

Yes, the receptacle is attached to the bottom of the disconnect. Based on memory, the height was around 16" I believe.

Roofing membrane damage noted?

No roofing damage.