Re: Fresh Air and Re-entry Air

[Guest guest]

Hello,I have one intake and one exhaust louver on building surface and they are quite close to each other.It likely cause some concern that the intake will take some discharged air from exhaust louver coming back to the building.Any one knows how much percentage is allowed for such kind of re-entry from any code or regulations?ThanksLou

[Guest guest]

In Australia the code requires 6 metres segregation between OA intake &

discharge.

If you are supplying scavenged air from the exhaust - this is no

different from mixing the air in the return plenum of the air handler

and this is usually acceptable if say high efficiency air filters are

used - this can be as little at 10%OA while if medium air filters are

used - this would be at a minimum of 30%.

The best method for measurement of this is using CO2 - CO2 ppm OA v

space return air, then the difference 100% used to determine the OA

quantity at supply plenum.

Note high efficiency filters are better than 90% No.1 test dust

retention at system airflow rates.

>

> Hello,

>

> I have one intake and one exhaust louver on building surface and

they are quite close to each other.

> It likely cause some concern that the intake will take some

discharged air from exhaust louver coming back to the building.

> Any one knows how much percentage is allowed for such kind of re-

entry from any code or regulations?

>

> Thanks

>

> Lou

>

[Guest guest]

This reminds me to ask. I have a new furnace and exhaust from it now

is only 6 feet from where I put a fresh air intake, on same side of

house, under an area where house overhangs the foundation. I placed

the fresh air intake there because it was handy and also the overhang

protects the fresh air intake opening from rain. It is only temporary

installed through wood put in to replace broken glass of basement

window, but I haven't figured out any other place to locate fresh air

intake. Is 6 feet, both under the house overhand too close for furnace

heat exhaust and then fresh air intake to be placed does anyone know?

I pointed out to installer of furnace location of fresh air intake,

which they hooked up to new furnace.

>

> In Australia the code requires 6 metres segregation between OA intake

&

> discharge.

>

> If you are supplying scavenged air from the exhaust - this is no

>

[Guest guest]

Is that legal in your building codes?

???

It shouldn't be..

It seems to me that any exhaust of combustion gases should be up

far and away from homes, also fireproof, as in chimneys... not down

low and next to side of house and windows..

and air intake...

This sounds like it could be a serious problem, if you are breathing

your own furnace exhaust.

> This reminds me to ask. I have a new furnace and exhaust from it now

> is only 6 feet from where I put a fresh air intake, on same side of

> house, under an area where house overhangs the foundation. I placed

> the fresh air intake there because it was handy and also the overhang

> protects the fresh air intake opening from rain.

[Guest guest]

Lou:

Most building codes that I am aware of state something like: “Building air-intake vents shall be located sufficient distance, both vertically and horizontally, to prevent re-entrainment of emissions from building exhaust ports, stacks, and vents.” This is not an exact quote, but is typical of the mechanical codes (e.g., UMC) that I work with. Moreover, from my experience, even when horizontal separation appears adequate, parapet walls and mechanical screens on building rooftops can create a “swimming pool” effect, that traps emission sources inside a confined area, and building air-intake vents suck it up. I have been on numerous investigations, and retained as an expert in several lawsuits, where this was the case. Thus, building codes may not be not adequate where other building systems interfere with atmospheric dilution and flow. And no...Studor Vent Caps offer only a limited solution to waste vent odors, and only if routinely serviced and replaced often.

For what it is worth.....

Hello,

I have one intake and one exhaust louver on building surface and they are quite close to each other.

It likely cause some concern that the intake will take some discharged air from exhaust louver coming back to the building.

Any one knows how much percentage is allowed for such kind of re-entry from any code or regulations?

Thanks

Lou

[Guest guest]

The IRC addresses the requirements partially. ASHRAE provides a lot of information on problems with recirculation of exhaust gases into intakes affected by wind pressure and wakes on the lee side of buildings. What you have described sounds like it could be the worst condition possible, especially if you are on the lee side of prevailing winds. Even on the windward side of a building, you have described a protected area that is probably prone to recirculation.

NIOSH has done some recent research on CO from generators with side exits from large houseboats and how much improvement can result from exhausting the gases through an elevated stack instead of adjacent to occupied decks.

Don Schaezler, Ph.D., P.E., CIH

ETC Information Services, LLC Cibolo, Texas

This reminds me to ask. I have a new furnace and exhaust from it now is only 6 feet from where I put a fresh air intake, on same side of house, under an area where house overhangs the foundation. I placed

the fresh air intake there because it was handy and also the overhang protects the fresh air intake opening from rain. It is only temporary installed through wood put in to replace broken glass of basement window, but I haven't figured out any other place to locate fresh air

intake. Is 6 feet, both under the house overhand too close for furnace heat exhaust and then fresh air intake to be placed does anyone know? I pointed out to installer of furnace location of fresh air intake,

which they hooked up to new furnace. >> In Australia the code requires 6 metres segregation between OA intake

& > discharge.> > If you are supplying scavenged air from the exhaust - this is no >

[Guest guest]

Thanks for the information. Perhaps I should just close it up until I

find better location for it. It was just there temporarily anyway, too

close to the ground.

>

> The IRC addresses the requirements partially. ASHRAE provides a lot of

[Guest guest]

Live, I had two different furnace bids and both said they would be

exhausting out the same spot. My mold furnace exhaust ran up next to

the chimney but they said they couldn't use that for some reason.

Actually exhausting under the 'bay window' overhang doesn't sound right

to me now either but at the time I just figured they knew what they

were doing...when will I ever learn? The pvc pipe that carries it goes

out to edge of overhang but still you are right. It doesn't sound too

good. It was Lennox dealer so I was thinking 'quality' but I should

know better than to trust anyone anymore to know what they are doing.

>

> Is that legal in your building codes?

>

> ???

>

> It shouldn't be..

>

>

[Guest guest]

Here is a picture of a thoughtlessly placed exhaust and air intake.

The picture is of the front of the house too, next to their front

door. This resulted in the death of a child apparently!

http://www.emmasmith.org/COVideos.htm

[Guest guest]

Thank you Ian and ,This is a pair of intake-exhaust that behaves breath in and out alternatively for a certain minuets of time interval to help heat recovery from the system for energy saving.Similar to your suggestion using CO2 measurement, I am simulating the particulate dispersion from the exhaust with wind from different directions and different wind speed with interference of study building and surrounding buildings. I can get the dilution rate distribution over the intake. So it will be possible to have an approximate number of "concentration" or percentage of the exhausted "dirty" air being taken by the intake.What I need to know is the acceptable percentage of fresh air, with this data, I will be able to select a proper

location to place this intake-exhaust pair. Can this 90% fresh air be a good criterion in best practice?ThanksLou To: iequality Sent: Friday, December 12, 2008 6:47:21 PMSubject: Re: Fresh Air and Re-entry Air

In Australia the code requires 6 metres segregation between OA intake &

discharge.

If you are supplying scavenged air from the exhaust - this is no

different from mixing the air in the return plenum of the air handler

and this is usually acceptable if say high efficiency air filters are

used - this can be as little at 10%OA while if medium air filters are

used - this would be at a minimum of 30%.

The best method for measurement of this is using CO2 - CO2 ppm OA v

space return air, then the difference 100% used to determine the OA

quantity at supply plenum.

Note high efficiency filters are better than 90% No.1 test dust

retention at system airflow rates.

>

> Hello,

>

> I have one intake and one exhaust louver on building surface and

they are quite close to each other.

> It likely cause some concern that the intake will take some

discharged air from exhaust louver coming back to the building.

> Any one knows how much percentage is allowed for such kind of re-

entry from any code or regulations?

>

> Thanks

>

> Lou

>

[Guest guest]

Barb:

Thanks for the link to the photos. They are alarming! They are appalling! In my opinion, negligence is definitely involved. If only the furnace exhaust was run vertically, up to and near the second story eave, the harm it caused might not have happened. Then again, why are these vents (both intake and exhaust) located right next to the front door?!? This, in and by itself, is stupid – no one wants grills, vents, and/or pipes right next to their front door! The whole arrangement is foolish.

Here is a picture of a thoughtlessly placed exhaust and air intake.

The picture is of the front of the house too, next to their front

door. This resulted in the death of a child apparently!

http://www.emmasmith.org/COVideos.htm

[Guest guest]

I did some reading up on high efficiency furnace exhaust and it said

that the high efficiency furnace exhaust burns the gas so completely

that there isn't much heat left in it, and so the exhaust is not very

hot, but warm. It says the exhaust is somewhat caustic though and can

affect area, bushes, etc it is exhausted near. Since it is only

operating in winter, I suppose most people are not out about side of

their house though. Anyway, I got something at Home Depot to put up a

baffle of sorts because arrangement concerns me. I'm going to call

Lennox and ask them to mail me installation instructions on my furnace

to read over myself. It also said that it burns fuel so completely,

that the little bit of water that is contained in gas, is released and

that explains why I have heard some water trickling down drain there,

an unusual sound in wintertime for me.

>

[Guest guest]

Steve

These high-efficiency furnaces are the norm in colder states and provinces and do very well indeed in heating in cold climates; they too are often oversized at installation and do not provide the comfort of a smaller unit. Almost no homes are every underheated with them, certainly not in climates like yours. Many of them come with a DC motor that drives the circulation fan; mine uses 84 W on continuous versus the old furnace that used 350 W on continuous low speed (600 W on cooling and 500 W on heating).

I am glad that you brought up the lack of need for metal in the flue pipe as the exhaust gases are cool enough to put your hand into (for a short while).

Jim H. White SSC

Re: Fresh Air and Re-entry Air

I saw this done (but through the roof, not the foundation) for the combustion air and exhaust for an extremely high efficiency furnace in a house we were looking at to buy here in Sacramento back 12 years ago. That particular type of gas furnace has a fan which drives combustion air into the combustion chamber, and is designed so the exhaust is low enough temperature to exit through PVC. The fan is required because there isn't enough heat energy in the exhaust to take it up a chimney under its own power.The furnace design uses a rather low temperature rise between return and supply air. I speculate it wasn't sufficient last week when the temperature here actually got below freezing overnight. But it's very energy efficient for its intended use.Note: that is combustion supply air, *not* air to be introduced into the house. Agreed that the installation does not look finished.Steve> > > >> > > > In Australia the code requires 6 metres segregation between OA > intake> > > & > > > > discharge.> > > >> > > > If you are supplying scavenged air from the exhaust - this is no> > > >> > >> > > > > >> >>

[Guest guest]

Barb

We have several trees close to the exhaust from our Lennox Elite series furnace and have noticed nothing; there should be nothing to cause problems as these furnaces produce very little CO and certainly no partly-burned hydrocarbons.

As you noted, most of the combustion water is condensed and has to be pumped out of the furnace; this is where much of the top-end efficiency comes from. They are often called condensing furnaces.

Jim H. White SSC

Re: Fresh Air and Re-entry Air

I did some reading up on high efficiency furnace exhaust and it said that the high efficiency furnace exhaust burns the gas so completely that there isn't much heat left in it, and so the exhaust is not very hot, but warm. It says the exhaust is somewhat caustic though and can affect area, bushes, etc it is exhausted near. Since it is only operating in winter, I suppose most people are not out about side of their house though. Anyway, I got something at Home Depot to put up a baffle of sorts because arrangement concerns me. I'm going to call Lennox and ask them to mail me installation instructions on my furnace to read over myself. It also said that it burns fuel so completely, that the little bit of water that is contained in gas, is released and that explains why I have heard some water trickling down drain there, an unusual sound in wintertime for me. >

[Guest guest]

The article I read exhaust is mildly caustic, or similar wording, and

that it could be a problem for nearby scrubbery, but some landscaping

scrubbery can be very delicate, Azaleas for example, which are very

popular around here but good to know it hasn't bothered your nearby

trees. I have flowers there in the summer that may not make it but can

plant something else easily. Thanks

>

> Barb

> We have several trees close to the exhaust from our Lennox Elite

series furnace and have noticed nothing

[Guest guest]

Please review the installation instructions for a high-efficiency

furnace located here;

http://www.allstyle.com/installationManuals/Furnace%20Manuals%20and%20Parts/VSAI\

nstallersManual.pdf

This shows acceptable practice for exhaust and intake ventilation for

high-efficiency furnaces. It would seem that this may be inadequate

when measured against standard installation practice (and possibly

contrary to local building code)but not grossly so.

To the poster who was surprised at the use of PVC pipe for exhaust and

intake for the furnace - high-efficiency gas furnaces use an

additional or larger heat exchanger than conventional furnaces, so

most of the heat is removed from the furnace exhaust. The residual

heat is scant enough that it will not melt a PVC or ABS pipe.

Incidentally, the intake pipe is only bringing in fresh air for

combustion, not for the dwelling airspace. In the worst-case scenario

of the two being too close together, the combustion efficiency of the

furnace would decline. Unless there is a grossly-compromised

installation, this has zero impact on the indoor airspace. And, of

course, the exhaust could be sucked into an open window, if you are

profligate enough to run your furnace with the windows open.

Vince Daliessio

EMSL Analytical

> >

> http://i145.photobucket.com/albums/r216/barb1283/FurnaceExhaust03.jpg

> > >

> > >

> >

> http://i145.photobucket.com/albums/r216/barb1283/FurnaceExhaust02.jpg

>

[Guest guest]

Barb

It is the opposite of caustic; the carbon dioxide and water make for a mild acid. The condensate does sting a bit on a scratch, but it is more like the strength of vinegar (not the same acid though).

Remember that less than half of what you find on the internet is correct; to some people any opinion is correct because there is no absolute truth. In a recent evaluation less than half of the professors presently ensconced in universities believe that there is such a thing as basic truth and that all opinions are equally valid. Oh what our society has shrunk to!

Jim H. White SSC

Re: Fresh Air and Re-entry Air

The article I read exhaust is mildly caustic, or similar wording, and that it could be a problem for nearby scrubbery, but some landscaping scrubbery can be very delicate, Azaleas for example, which are very popular around here but good to know it hasn't bothered your nearby trees. I have flowers there in the summer that may not make it but can plant something else easily. Thanks>> Barb> We have several trees close to the exhaust from our Lennox Elite series furnace and have noticed nothing