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Old 10-26-2011, 07:46 PM   #1
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Metal duct from furnace leading through a basement hole


I have a metal duct connecting the exterior through a basement wall to the oil furnace. The connection goes into the front of the furnace where the controls are and the cover for the furnace has a square hole on the bottom left as seen in the pictures. I fear it is introducing very cold air into my house (Boston) and causing more energy consumption during winter. The ocassional furnace cleaner or energy auditer have said it is not necessary you can remove it or said the furnace requires this oxygen or its life span will decrease. Mixed suggestions...

Should I remove the duct and patch up the basement hole?


Some details:
I have noticed white substances on the basement wall. I imagine this is because their is too much humidity in the basement. Maybe the hole is causing it.
1995 house so I assume just as old system
Forced air oil furnace system
Basement is divided by a wall, the other side is a garage.
2 living floors and attic sit above the whole basement including the garage
Fiberglass insulation on basement ceiling and against dividing wall. Where the foundation meets the house framing has been foam sealed.
Whole house humidifier is connected to furnace but I have never used it.

Thank you in advance. Any help I can receive is extremely valuable to me.















Last edited by Arjun007; 10-27-2011 at 09:28 PM. Reason: added 3 pictures of the furnace with the cover off. Just remember the cover has a square hole on the bottom left. see pic 1
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Old 10-26-2011, 08:07 PM   #2
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Metal duct from furnace leading through a basement hole


no expert on oil but it looks like someone brought in fresh air for combustion purpose ....I don't think you need this because house is drafty enough for normal combustion to take place..just my thinking perhaps some others would help??????

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Old 10-27-2011, 02:01 PM   #3
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Metal duct from furnace leading through a basement hole


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no expert on oil but it looks like someone brought in fresh air for combustion purpose ....I don't think you need this because house is drafty enough for normal combustion to take place..just my thinking perhaps some others would help??????
Thank you for your response. I also appreciate if others are able to chime in.
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Old 10-27-2011, 02:37 PM   #4
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Metal duct from furnace leading through a basement hole


how about a pix of the front with the cover off and pointed to the up right corner to see the round duct connection within the burner section.if it does go into the burner section for fresh air for combustion it will never mix with the house air or temper it totally seperate.that humidifier looks kinda wierd with the blow thru ducting seems it humidifies discharge air then cycles back to the return...also let other kick in on your system then step back...hope for that pix of the inside panel burner section....
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Old 10-27-2011, 03:59 PM   #5
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Metal duct from furnace leading through a basement hole


Looks like a combustion air intake. As above, a pic with the furnace panel off will help to confirm.
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Old 10-27-2011, 09:35 PM   #6
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Metal duct from furnace leading through a basement hole


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how about a pix of the front with the cover off and pointed to the up right corner to see the round duct connection within the burner section.if it does go into the burner section for fresh air for combustion it will never mix with the house air or temper it totally seperate.that humidifier looks kinda wierd with the blow thru ducting seems it humidifies discharge air then cycles back to the return...also let other kick in on your system then step back...hope for that pix of the inside panel burner section....


I edited the first post with 3 pictures of the furnace with the cover off. I thought the cold air would mix with the house air because the cover has a hole and the furnace has holes at the top - so the controls area is not even close to being sealed. I figured the cold air would just go through the holes and cause my basement to drop in temp and impact the rest of the house. Potentially even contribute towards pipe freeze maybe.

I was also questioning the humidifier. The humidifier is placed on the duct where the heat rises to distribute to the house and a round duct connects it to the return. I don't use it so I wondered if removing it would increase my heating system efficiency. Let me know your thoughts please. I already had the waterline disconnected (it was a self piercing saddle valve.)

Thank you!!!!!

Last edited by Arjun007; 10-27-2011 at 09:43 PM.
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Old 10-27-2011, 09:48 PM   #7
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Metal duct from furnace leading through a basement hole


that humidifier is definitly bypassing heated air back to the return and short cycling heated air up into the space.that fresh air duct must chill out that basement..remove it just off the elbow mounted onto the furnace and cycle the heat put you face near the elbow see if the oil burner is drawing air thru there with that furnace cover back on on...if it is minimal i would remove that piece going out and remove the outside metal work...but try that test first seems like an addon as said the basement is atmospheric with loads of free air.... remove the humidifier and the duct to the return and cover all opens
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Old 10-28-2011, 12:46 PM   #8
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Metal duct from furnace leading through a basement hole


Thank you very much everyone!

In patching the holes for the humidifier. What's the process? Is there any specific type of sheet metal or screws I should be using? Should I also use caulking to connect the piece to the furnace? What do you recommend for insulating the piece on the heat stack?


Also - I had a follow up question - How often does one need to clean the chimney connected to the furnace?

I am thinking to buy a chimney rod / brush kit from amazon to do it myself. I read people do the cleaning from within their basement. Is the panel in picture 6 the one I would remove and insert the chimney brush/rod from? (The duct runs past a damper before connecting to the chimney stack which goes straight up. The connection at the chimney stack which runs straight up is more like a T since a small piece of the chimney stack still runs down towards the floor about a few inches past the connection. So its not an elbow.

Thanks again!!!
D
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Old 10-28-2011, 01:29 PM   #9
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Metal duct from furnace leading through a basement hole


You have what is called a by-pass humidifier.It is installed correctly.Now if you don't use it I guess taki8ng it down and patching the holes is the way to go.If it were me I would use a normal RTV cauck and 1/2 " metal screws.
Again if it were me I'd fix the humidifier ande use it ,but its your choice.
The stack from the furnace to the chimney should be removed carefully as it looks to be loaded with soot.Use a shop vac with large bags and be aware that you will in the end be using probably 3-4 bags for the soot vacuuming.You will also need to scrap and vacuum the combustion area of the furnace.Be carefull about the actual combustion chamber though as that is very brittle and will crumble easily.It should be looked at anyway because it might already be damaged and causing all that soot.
Now here is where I will strongly suggest that you get a pro to come in with instraments and set your burner up correctly.If that costs you say $150 you will save at least $400 over the length of the heating season and most likely avoid some kind of a break down which could cost $400 all by itself.
Now the thing that concerns me is the obivious soot showing in the burner compartment.It either needs a very good cleaning or it was back drafting and that is why they installed that fresh air intake to give it more combustion air.
Go0od luck to you.
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Old 12-10-2011, 08:58 PM   #10
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Metal duct from furnace leading through a basement hole


I capped the return end and the humidifier as seen in the below picture. (I thought this would be easier for me.) The airflow out of the heating vents and into the returns in the living quarters has increased significantly which I love. However, I think it has created a problem. I have noticed my furnace cycles on and off more frequently now (it comes on after every few minutes of rest to heat up and provide half a minute of heat blowing through the registers). I set the thermostat at 66 and it is only maintaining 65 degrees while cycling.

I am thinking my furnace is not able to eject all the hot air before a high temperature limit is reached and the furance shuts itself off for safety. If it keeps doing this my guess is the heat exchanger will crack. My air filter was replaced just recenlty and when I checked it was not dirty at all. I use a poly filter which does not restrict air flow. The furnace had its annual cleaning couple weeks ago before I made this modification.

What do you guys think? Is this really what is happening you think? Should I put the bypass pipe connecting the humidifier and return back? Maybe I'm just over thinking it and everything is within reason. Thank you once again!

(It is currently 29 degrees outside.)


Last edited by Arjun007; 12-10-2011 at 10:35 PM.
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Old 12-10-2011, 10:20 PM   #11
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Metal duct from furnace leading through a basement hole


You have an uncovered fan/limit control in your furnace that should give you the air stream temp in your furnace. What is the limit temp nib set at? ( the first nib is for the fan "off" temp, next is the fan "on" temp and the highest temp nib would be the limit temp)

Is your air filter or coil dirty? Do you have heating outlets or return air grills shut off,covered or inserted with their own filters? Are the fan cage fins filled with dust?
If just closing off an 8" opening in your return air raised your running temp to limit, then your operating temp was too high to begin with.
Reducing the heating output or speeding up the air movement through the furnace is the next option once the above causes of overheating are eliminated and if the fan /limit control is working properly.

Last edited by how; 12-10-2011 at 10:25 PM.
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Old 12-11-2011, 04:14 AM   #12
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Metal duct from furnace leading through a basement hole


Return drop is probably too small. Need more return air. What size is your return drop.
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Old 12-11-2011, 01:08 PM   #13
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Metal duct from furnace leading through a basement hole


I have more pics here. From what I can make of it:

nib #1 90 degrees (off)
nib #2 120 degrees (on)
nib #3 150 degrees (off max)

Is this set correctly or should it be adjusted and if so adjust to what and how do i adjust it?

The furance had its annual cleaning so it shouldn't be dirty but when checking the blower fan fins I did see some dust on each fin. The air filter is not dirty and its the flat fiberglass kind that does not restrict air flow - I put it in less than a month ago. I don't know how to check if the coils are dirty. All returns and ducts are open and unblocked but one return has the couch near it as seen in the pic. Do you think this is a problem? (couch is too big). And actually their is one heating duct in the basement that has always been closed. it was cut into one of the main pipes and opening it causes sheet metal to go up into the duct to divert air into the basement but then the duct that comes after it would receive less air. So I wouldn't think this would be an extra register but more of a redirect.

The part I removed was a 6" pipe.

As a note the heat was off overnight - this morning I fired it up and the furnace brought the house from 52 degrees to 63 degrees without turning off in about 27 minutes. The thermostat was set to 64 though. (So if it did that I'm assuming its not overheating?)

It seems to always be a degree short of the thermostat setting so I think it may keep calling for heat and when it does it only ejects heat for about 30 seconds or a minute which doesnt make up the one degree so it keeps donig this cycle every few minutes.

The returns measure:
16 x 6 (3 of these on the first floor)
16 x 16 (1 of these on the ceiling 2nd floor outside 3 bedrooms)
(I'm not sure if this is how you wanted me to measure, please advise if it should be measured a different way.)

House is about 1200 square feet sitting on a garage.












Last edited by Arjun007; 12-11-2011 at 01:16 PM.
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Old 12-11-2011, 01:16 PM   #14
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Metal duct from furnace leading through a basement hole


I don't work on oil furnaces (gas equipement only) but I don't know why your limit control nib isn't set on 200F instead of 150F. Unless someone can tell me why oil furnaces require a lower limit temp than gas, I think you've found your problem. You might want to wait on changing it until an oil guy speaks up.

To adjust the fan/limit control hold the whole dial steady in place and just slide the nib on the 150F mark to the 200F.

PS. The picture of your wiring to the lower part of the fan/limit control is too dark to inspect properly. I just want to confirm that there are three wires conecting to the fan/ limit control in addition to the bridge pigtail.

Last edited by how; 12-11-2011 at 01:43 PM.
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Old 12-11-2011, 01:50 PM   #15
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Metal duct from furnace leading through a basement hole


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I don't work on oil furnaces (gas equipement only) but I don't know why your limit control nib isn't set on 200F instead of 150F. Unless someone can tell me why oil furnaces require a lower limit temp than gas, I think you've found your problem. You might want to wait on changing it until an oil guy speaks up.

To adjust the fan/limit control hold the whole dial steady in place and just slide the nib on the 150F mark to the 200F.

PS. The picture of your wiring to the lower part of the fan/limit control is too dark to inspect properly. I just want to confirm that there are three wires conecting to the fan/ limit control in addition to the bridge pigtail.

From the picture and looking at the fan limit switch it looks like its got a metal stop at 150 which the nib prolly can't go past. Or is this normal and it will still move?

As for the wires, there are 2 wires and one U wire with both ends connected to the switch - I imagine this is what you are referring to as a bridge?

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