[thracianspec]

Hi All,

I can't post a picture so I apologize, but it perplexes me why I have an outside air intake at the top of my furnace? I have a dual stack flue, and I thought the purpose of this was to pull in outside air to help the furnace.

My question is when I'm using my A/C it pulls cool air in from my return, but also air from the outside (through this intake) which is 100 degrees, and mixes it? I can't understand the logic behind this?

I found this intake by accident as I was in the attic and noticed the flex pipe had become disconnected (yes the idiots used ducktape (not duct tape so at that point it was pulling in 140 degree hot air and mixing with my return air.

Again, what is the point of mixing hot air from the outside with my return air?

I have a Nordyne/Intertherm 703911B (model: M1MB 070A BW) 3 Ton Furnace with a Coleman 4 ton Coil/compressor

Thank you

 

[BaldLoonie]

The air is a requirement in mobile homes so air used by the burning process comes from outside, not in the living space. It should not be getting in your return air in any way.

 

[firecontrol]

Mobile home furnaces have a fresh air inlet into the blower compartment, it should have a motorized damper on it that closes it off when the furnace blower isn't running. The intake is located on the roof.

This arrangement is to bring fresh air into the home to mitigate VOC's and other air contaminates present in every home. Building/HVAC code requires fresh air intakes of one form or another in all homes for this same reason.

 

[pecmsg]

Mobile home furnaces have a fresh air inlet into the blower compartment, it should have a motorized damper on it that closes it off when the furnace blower isn't running. The intake is located on the roof.

This arrangement is to bring fresh air into the home to mitigate VOC's and other air contaminates present in every home. Building/HVAC code requires fresh air intakes of one form or another in all homes for this same reason.

I’d like to see that regulation if you don’t mind!

 

[thracianspec]

I have seen this unit with a damper on youtube, but mine does not have a damper nor any mechanic device to control one. It was sucking gobs of hot air into the blower motor so I plugged it up for now..until i learn more...doesn't make sense and was killing my cool air return.

 

[BaldLoonie]

I stand corrected. Didn't know that intake was for house air not combustion.

 

[pacnw]

OP, confirm we are talking about a mobile home as it was assumed in one of the posts.

Ventilation air is an ever changing requirement, state but not sure if federal. In my state there is now no requirement for intake, but for an exhaust fan that runs 24/7, like a bathroom fan, sized for the square footage of the home(some may require multiple fans).

 

[thracianspec]

Thanks for your replies, this is a manufactured home.
Again, I can't understand how sucking in hot air helps the A/C unit do it's intended job??

 

[flanders]

I was told years ago that it is to keep the coil from freezing due to the horrible ductwork commonly found in mobile homes. Not sure if that's true though.

 

[thracianspec]

I'll be honest the duct work is actually not that bad in at least my manufactured home (Karsten) however, the starter collars were just double sided taped onto the trunk and they were leaking badly so I fixed that the correct way. Other than that the rigid trunks are well done.
My coil is not even close to freezing over as I've been in that compartment many times.

Oddly, I have another home that is identical and I just happen to be updating some new 12" flex runs and noticed a lot of condensation. When I opened the coil compartment the entire coil was a block of ice.. I've never seen that before and I had just had the HVAC tech check the R22 level and it was normal.. Really odd situation, I since defrosted it and it works perfect...no idea why it just froze over out of nowhere, the vents or something must have been blocked, but weren't upon inspection. Oh well, waiting to see if it happens again...but this is off topic.

 

[pacnw]

Thanks for your replies, this is a manufactured home.
Again, I can't understand how sucking in hot air helps the A/C unit do it's intended job??

It has NOTHING to do with the functionality of the heat or cool. It is, as stated, to introduce outside air to dilute indoor pollutants. This started when houses began to get air sealed. Not enough outside air was introduced, it used to just flow in normally due to poor construction and lack of insulation/house sealing at times when energy was no big deal, to mitigate the indoor pollutants AND the organic growth caused by high moisture content trapped in the house.

Overall, you are best to allow it to do its job. The majority of people don't understand and those that do feel they know better and close/disconnect/bypass the ventilation air.

Depending on the age, there may be an interlock to an exhaust fan(bathroom or laundry). This pulled the polluted air out at the same time fresh air was introduced. Some even had their own timer that brought on the furnace fan independent of any heat/cool operation.

 

[pacnw]

I was told years ago that it is to keep the coil from freezing due to the horrible ductwork commonly found in mobile homes. Not sure if that's true though.

False.

Told to you by someone who does not know what the purpose is.

 

[thracianspec]

Pacnw, does this assume then that all new hvac systems introduce outside air?

 

[flanders]

False.

Told to you by someone who does not know what the purpose is.

Mobiles are built so poorly that they don't need additional outdoor air introduced. It's constantly coming in on it's own.

 

[pacnw]

Mobiles are built so poorly that they don't need additional outdoor air introduced. It's constantly coming in on it's own.

OP stated manufactured, which is different than mobile.

Many newer mobiles are fairly tight, some even rated Good Sense or Super Good Sense(or something like that indicating energy efficiency).

 

[pacnw]

Pacnw, does this assume then that all new hvac systems introduce outside air?

As I stated, I am not sure if the regulations are state or federal mandates.

Also, as I stated, in my state there is no longer outside air requirements but an exhaust fan must be running 24/7.

 

[firecontrol]

I’d like to see that regulation if you don’t mind!

HUD has jurisdiction over manufactured homes and has mandated fresh air ventilation for as long as I can remember, or at least since they identified the health risks of formaldehyde out-gassing and other indoor air contaminates.

As for the code specific to requiring fresh air intakes, I can only speak to my state. Either you provide a "Skuttle" style fresh air intake to the HVAC forced air system or you install a whole home HRV/ERV or you don't pass inspection on new home construction.

Your latest post states your state only requires that an exhaust fan run 24/7, how does the air that the fan(s) are exhausting get replenished into the home?

For 30+ years I've seen every mobile home style furnace installed in a manufactured home located on the main floor and a standard efficiency style has had a 4" vent connected to the blower compartment and terminated outside.

 

[pecmsg]

This is where it gets confusing.
Specs for Mobile homes are they the same as those for Manufactured Homes!

 

[vstech]

The ductwork is the same...

A single 3-3/4 x 10 metal trunk down each section with registers cut into the floor on top, then a roll of insulation covered by crawlspace webbing...

Horrible.

 

[Mr Bill]

All the mobile homes in Houston I've ever worked on, has a special roof jack, the introduces fresh air for combustion down one area of the jack, and releases flue gasses out the other area. I have installed many of these, they are confined to the combustion chamber, they have no effect at all on your ac. Maybe some of you are talking about the old school ones, where two pipes are run down into the furnace area, one lower than the burners and one higher, I haven't see any like that around here since the 70's.