Sealed Combustion Furnace Draws Air From Inside - HVAC - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 01-08-2012, 10:55 PM   #1
Member
 
Join Date: Aug 2011
Location: Louisville, KY
Posts: 128
Rewards Points: 75
Default

sealed combustion furnace draws air from inside


Hi All,

We recently bought a house and I'm trying to get around fixing and changing staff. I know nothing about HVAC, and I'm dumbfounded about the following.

I seem to have a sealed combustion chamber furnace (90% efficiency sticker on it), but the intake pipe ends shortly after it comes out of the furnace. That is, it draws air from the room it is in. It is in a fairly large enclosed space together with the gas water heater. I was trying to figure out if this "one pipe" installation is even allowed for this type of furnace, but I have trouble finding anything about this model. There is an "ArcoAire" banner on the front and 2 model numbers inside: NTG9100FHA2, and GNM100N16A2.

An HVAC guy inspected the furnace before I bought the house and he found everything fine, but I don't trust inspectors any more. (See my other posts in the plumbing forum.)

It doesn't seem like terribly difficult to install a PVC intake pipe through the wall (so it is especially puzzling why the previous owner didn't get that done). Are there any pitfalls I should know about? Would I have to get this inspected when it's done?

Thanks in advance,

Advertisement


Last edited by csab_; 01-08-2012 at 10:58 PM. Reason: (forgot to say thanks)
csab_ is offline   Reply With Quote
Old 01-08-2012, 11:28 PM   #2
Newbie
 
Join Date: Jan 2012
Posts: 22
Rewards Points: 10
Default

sealed combustion furnace draws air from inside


It is quite common to see 90%+ furnaces installed in this way, there is really nothing wrong with it as long as there is combustion air in the room. (outdoor air supply). If not then it must be added.

Advertisement

Baldrick is offline   Reply With Quote
The Following User Says Thank You to Baldrick For This Useful Post:
csab_ (01-08-2012)
Old 01-08-2012, 11:42 PM   #3
Member
 
Join Date: Aug 2011
Location: Louisville, KY
Posts: 128
Rewards Points: 75
Default

sealed combustion furnace draws air from inside


No, the room doesn't have any opening to the outside, not even a window, if that's what you mean. It's not all that well sealed though.
csab_ is offline   Reply With Quote
Old 01-09-2012, 12:21 AM   #4
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,552
Rewards Points: 620
Default

sealed combustion furnace draws air from inside


With the PVC air intake open to the furnace room if it is loose enough (able to get all the air it needs for furnace combustion) offers
Less potential air intake obstruction from snow/ kids toys/ animals/nests/ etc.
A slightly higher temp rise.
A loss of heated air that you've already paid for.
The potential for air starvation of the furnace as renovations make the home and furnace room more air tight over time.
The potential of causing other local atmospheric gas appliances to spill CO.
Slightly less condensate to remove.

A direct PVC outside air supply to the combusion chamber offers
More potential for intake obstructions.
A slightly lower temp rise
No loss of preheated house air.
No cause of problems for other atmospheric gas appliances.
Slightly higher levels of condensate to remove.

If your HWT is not power vented, I'd test it for spillage right now at it's draft diverter while the furnace is running with the house windows & doors closed and the clothes dryer running.
You do need outside air into your combustion chamber either directly or via an outside air supply into the furnace room.

Last edited by how; 01-09-2012 at 12:40 AM.
how is online now   Reply With Quote
The Following User Says Thank You to how For This Useful Post:
csab_ (01-09-2012)
Old 01-09-2012, 01:07 AM   #5
REP
Member
 
Join Date: Jul 2011
Posts: 615
Rewards Points: 500
Default

sealed combustion furnace draws air from inside


Since your basement isn't sealed tghat tightly,what you have is alright.Now if it were tight i.e. doors would move if you shut the basement door with force then you would want to pipe the intake outside.Everything HOW layed out for you is true sop there is that.
If I were you and everything was running good,I'd leave it alone.
There is no sense in waking up the watch dog if there is nothing to watch.
REP is offline   Reply With Quote
The Following User Says Thank You to REP For This Useful Post:
csab_ (01-09-2012)
Old 01-09-2012, 04:05 AM   #6
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,519
Rewards Points: 4,682
Default

sealed combustion furnace draws air from inside


That furnace by code, when installed using the room' air for combustion. The room needs to have a volume of 5,000 cubic foot. Add in the water heater's requirements, say a 40,000 BTU input water heater, and you bring that requirement up to 5,200 cubic foot. So if your basement ceiling is 8 foot. Your room needs to be 650 sq ft in area. Or you need grilles communicating to other areas to leave the combustion air come into that room.

Or run the intake pipe.
beenthere is online now   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
csab_ (01-09-2012)
Old 01-09-2012, 11:54 AM   #7
Member
 
Join Date: Aug 2011
Location: Louisville, KY
Posts: 128
Rewards Points: 75
Default

sealed combustion furnace draws air from inside


Thanks all, for the input.

how: One of the first things I did was to check for spillage at the draft diverter of the water heater. Although I'm not sure how to do it exactly, I played around with a candle to see how the flame leans, but it seemed to lean toward the chimney pipe (very slightly though). I also placed a CO monitor to the furnace room overnight, but it stayed at 0 (means less than 30 ppm).

beenthere: the room is certainly less than 650 sq feet. LOL, that's bigger than our first apartment was.

I decided to run the the pipe. Thanks for your valuable advice.

Now the only question is: why did the HVAC "expert" say there is no concern with my system.

Also: does anybody know if I need to get this inspected when it's done?

Last edited by csab_; 01-09-2012 at 01:12 PM.
csab_ is offline   Reply With Quote
Old 01-09-2012, 01:01 PM   #8
Part of the Clover Leaf
 
Join Date: May 2011
Location: NW Burbs of Detroit Mi.
Posts: 1,107
Rewards Points: 500
Default

sealed combustion furnace draws air from inside


It's always best to run the combustion air from outside. I have seen too many basement install that have all kinds of plastics and cleaning chemicals stored near the furnace.
\Taking combustion air from the home in this case would tear up the heat exchanger because of the air mixing with the out gassing/aspirating of the plastics and cleaners. The intake air becomes corrosive and can perforate a a heat exchanger in one season
hvac5646 is offline   Reply With Quote
The Following 2 Users Say Thank You to hvac5646 For This Useful Post:
ben's plumbing (01-09-2012), csab_ (01-09-2012)
Old 01-09-2012, 01:36 PM   #9
Member
 
Join Date: Nov 2008
Posts: 279
Rewards Points: 252
Default

sealed combustion furnace draws air from inside


How said:

A direct PVC outside air supply to the combusion chamber offers
More potential for intake obstructions.
A slightly lower temp rise
No loss of preheated house air.
No cause of problems for other atmospheric gas appliances.
Slightly higher levels of condensate to remove.

Frequently overlooked is that outside air enhances comfort, in that it substantially reduces or totally eliminates, static shocks.
veesubotee is offline   Reply With Quote
The Following User Says Thank You to veesubotee For This Useful Post:
csab_ (01-09-2012)
Old 01-09-2012, 05:02 PM   #10
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,519
Rewards Points: 4,682
Default

sealed combustion furnace draws air from inside


Quote:
Originally Posted by csab_ View Post
Thanks all, for the input.

how: One of the first things I did was to check for spillage at the draft diverter of the water heater. Although I'm not sure how to do it exactly, I played around with a candle to see how the flame leans, but it seemed to lean toward the chimney pipe (very slightly though). I also placed a CO monitor to the furnace room overnight, but it stayed at 0 (means less than 30 ppm).

beenthere: the room is certainly less than 650 sq feet. LOL, that's bigger than our first apartment was.

I decided to run the the pipe. Thanks for your valuable advice.

Now the only question is: why did the HVAC "expert" say there is no concern with my system.

Also: does anybody know if I need to get this inspected when it's done?

Depends on your local codes if you need it inspected or not.


many installers either don't know, or are too lazy to run it.
beenthere is online now   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
csab_ (01-09-2012)
Old 01-09-2012, 08:27 PM   #11
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,552
Rewards Points: 620
Default

sealed combustion furnace draws air from inside


I'd tell the installer that you plan to have it inspected (even though you may not) so they don't install it near a gas meter or dryer outlet or low enough to be covered by snow or.....

Quote
Frequently overlooked is that outside air enhances comfort, in that it substantially reduces or totally eliminates, static shocks.

Air ducted into a combustion chamber and exhausted via inducer motor will not have any effect on the homes air humidity (static charges) but if you are talking about a general fresh air vent into the furnace room then yes it reduces static charges and brings in air that is often 5 - 10 times fresher than typical off gassing house air.
how is online now   Reply With Quote
Old 01-09-2012, 08:35 PM   #12
Member
 
Join Date: Oct 2011
Location: pa
Posts: 4,633
Rewards Points: 2,580
Default

sealed combustion furnace draws air from inside


you did the right thing after seeing the room size was less than 650 sf installing the fresh air pipe will make sure the furnace has the proper combustion air...
ben's plumbing is online now   Reply With Quote
Old 01-09-2012, 09:22 PM   #13
Member
 
Join Date: Aug 2011
Location: Louisville, KY
Posts: 128
Rewards Points: 75
Default

sealed combustion furnace draws air from inside


Quote:
Originally Posted by how View Post
I'd tell the installer that you plan to have it inspected (even though you may not) so they don't install it near a gas meter or dryer outlet or low enough to be covered by snow or.....
The installer would me yours truly.

The only potential problem I see is that I plan to bring it out close to the exhaust.
csab_ is offline   Reply With Quote
Old 01-10-2012, 01:43 PM   #14
Member
 
Join Date: Nov 2008
Posts: 279
Rewards Points: 252
Default

sealed combustion furnace draws air from inside


Quote:
Originally Posted by how View Post

Quote
Frequently overlooked is that outside air enhances comfort, in that it substantially reduces or totally eliminates, static shocks.

Air ducted into a combustion chamber and exhausted via inducer motor will not have any effect on the homes air humidity (static charges) but if you are talking about a general fresh air vent into the furnace room then yes it reduces static charges and brings in air that is often 5 - 10 times fresher than typical off gassing house air.
Yes, it will not have a (direct) effect on humidity. It will prevent the air infiltration that occurs when non-direct vented furnaces operate.

The infiltration of outside low humidity air is what causes the lowering of humidity in the house. Since downsizing from a low efficiency furnace to a direct vented unit, shocks are GONE. These last 2 winters are testimony to that.
veesubotee is offline   Reply With Quote
Old 01-10-2012, 08:47 PM   #15
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,552
Rewards Points: 620
Default

sealed combustion furnace draws air from inside


outside low humidity air ????

Sounds probable but to a Vancouverite "outside low humidity, is completely theoretical. Just looking up without getting a mouth full of rain water is the closest we get to low humidity around here.

Advertisement

how is online now   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Combustion air fan on my furnace BCSapper HVAC 4 02-14-2014 01:46 PM
Furnace condensate drain/trap issue SteveC HVAC 33 12-27-2012 12:46 PM
Venting a new furnace? Mike in Arkansas HVAC 6 07-27-2011 11:40 PM
Payne PG9YAB high efficiency 95% furnace water draining problem jchen64 HVAC 9 12-06-2010 07:42 PM
furnace combustion air from attic rvegab00 HVAC 3 12-07-2009 09:18 AM




Top of Page | View New Posts