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.

 

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....:wink:

 

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!!!!!

 

Looks like a combustion air intake. As above, a pic with the furnace panel off will help to confirm.

 

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

 

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

 

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.

 

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.)

 

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.

 

Return drop is probably too small. Need more return air. What size is your return drop.

 

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.

 

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?

 

If you really have only two wires going to the fan/limit control then it can function as a fan control or a limit control, but not both. The way it seems to be wired, it will make or break the electrical current through the bridge for those two main wires so that as a...

Fan circuit it will turn on the fan at 115F and turn it off at 90F BUT it will also turn off the fan if the temp exceeds 150F when the furnace would really need the fan to be trying to keep the temp in check.

If it is solely a limit control then its bizarrly over wired since those two main wires would only need to be connected to the upper and lower RH side connection points to work properly. No bridge would be needed.

I'd wait for an oil guy to say if oil furnaces are designed to limit at a lower temp than gas. I hope he can also say where the real
fan control is since I can't see a safe way that this control could do it all without a third wire.

 

Fan off should be 110 or so, and fn on 140 or so. Limit on oil can be set to 200, 150 is too low.

 

Thanks to both of you for your information. I'm sorry beenthere but are you giving this information knowing how the oil furnaces work? I just want to be sure I'm not doing something that could harm my system or my family.

Thank you both once again.

If other oil experts are able to also provide their input or confirmation, I would greatly appreciate it.

 

Hey beenthere
Whats your take on a fan/limit control with only two wires hooked up to both the fan & limit output connections and connected via the lower pigtail?

 

sorry so much for the confusion but i took another look and did find the 3rd wire. it was well hidden under/behind the other one.

 

Cool, makes everything simple and understandable. Hold the dial of the fan/limit control so that it will not move and try to slide the nib and the stop to the 200F position. If the stop will not allow the nib to be slid up to the 200F position then the fan/limit control will need to be replaced with one with the same internal bimetal arm length.
This is all 120V stuff so make sure the breaker is off before you play and write down the colored wire and their fan/limit placement positions before swapping it out. A new fan/limit control will have a small removeable link that should be left alone that takes the place of the short orange wire.

 

Although you guys are a tremendous help, I have to be honest I get nervous making some changes. Especially after reading online some websites saying its dangerous to change the limit setting - peace of mind can be a hard thing to over come lol.

We moved in to this house a couple years back and fortunatley I was able to find the manual!!! It also says the factory set limit is 200 and should not be adjusted. So someone must have adjusted it for a reason. Seeing the black mark on the front of the furnace and the fresh air line installed for combustion, I'm guessing some oil guy reduced the limit and installed the fresh air line because the flame was backdrafting.

I will for the time being increase the limit to 170 and see how that works. I guess I will adjust up more if necessary but want to be sure the system doesn't backdraft again. Is my concern legitimate you think? Would a 200 setting increase the likelyhood of a backdraft?

Thanks again!!

 

I tried to slide the nib with a flat tool while holding the round piece in place with my hand and it would not slide. I tried with quite a bit of force and it still would not move.

So I guess I need to replace the part. When I buy a new one, how do I know which one to buy? And where to buy from? I'm guessing if someplace had it locally it would be quicker than shipping it.

 

Your concerns are reasonable.
Another reason techs adjust the settings on the fan/ limit controls is to compensate for the fan/limit control aging and wearing out which can show up as the control not responding properly to the real temp of the furnace.
The proper way to deal with the difference between actual furnace air stream temp and what a fan/limit shows, is to replace the fan/limit control.
The detail to watch for in replacing the fan control is to pull the old one and match the length of the spiral bimetal arm that protrudes into the furnace. You are talking about a pretty common $100.00 buck part from a general HVAC supply house. Many will balk at selling gas control parts to folks without gas licenses but will probably be OK with the part you are after. The arm of the fan/limit will probably range between 5 and 12 inches but chose the identical one to your old one unless you can find out what your furnace was originally suposed to have.

 

Thanks for all the info.

Do you think that adjusting the blower speed for the heat could also solve the problem? The yellow wire (heat) is set to low currently.

The manual says the Purple in High and the Yellow in Low would be the best for "normal applications"

 

I work on a lot of oil furnaces. So yes, my advice is from knowing how they work.

Fan off at 100 tends to give a somewhat cool air at the supplies that are the furtherest from the furnace, so 110 works better. good chance someone put in a fan limit that was used for olde gas furnaces, and that is why the limit is set to 150 max.

Standard oil furnace fan limit has its high limit set at 200.

 

I installed a new fan limit switch from grainger. (I left the orange wire out as instructed by "How")

http://www.grainger.com/Grainger/HONEYWELL-FanLimit-Control-2E820?Pid=search

3 nibs are as follows:
100
125
200

the fan on temp 125 was reached and the fan would turned on but in about 15 seconds the dial went to the fan off setting (100) and the fan goes off. The burner continues going on and this keeps repeating to create 15 second fan on times.

I adjusted it to 150 and the fan off setting to 90. The fan stayed on about 30 seconds before turning off at temp 90. It repeat getting to 150 turn on and 30 seconds back to 90 and turn off and so on since the house thermostat temp hadn't been reached.

What is the normal behavior for a furnace?
Should the fan coming on bring it to the fan off limit that fast?
What do I need to do? Please help. Thank you!

 

What was the probe length of the old fan/limit compared with the new one?
I would keep turning down the fan off nib on your fan/limit control until the temp coming out of your heating vents at the end of the heating cycle was barely luke warm.
The "on" temp nib can also be adjusted. Too high and you are losing that extra heat that is going up your chimney vent before the fan comes on. Too low and your unit can start short cycling. I'd leave that "on" nib where it is for now.
Once you got the furnace fan to run continuously through the heating cycle by adjusting the "off" nib down, then watch what the normal operating temp on the fan control is and tell us.
Your original set up for the humidifyer would have been helping to preheat the return air (as a direct bypass) and the original fan/limit control would have be adjusted accordingly. The options on preventing your fan from shutting down in the middle of the heating run are,
(1) lower the fan off nib temp. (a higher "on" won't help, its high enough already)
(2) lower the fan speed (probably will make it less fuel efficient).
(3) reconnect the humidifyer line from the supply plenum to the return.

I would also use the wireholder that came with your fan/limit control on all three wires. The picture to these old eyes looks like the 120V lines are unsecured where they transit the control case.

 

They were both 11.5 inches

I guess I will take out the new fan limit control - replace the old one and hope grainger will let me return the one i just bought.

Replace the connection between the humidifier and the return.

I was hoping to increase the air flow in the house by removing that humidiifer connection and it did do that but it created more problems. It seems messing with the settings in this new setup would be less efficient.

I guess as the old saying goes...... if it ain't broken....


(thank you for all your help though - I definitely wanted to test out my theory and I couldn't have done it without you! Thank you How and beenthere!)

 

Hold your horses there Bro.
If you are getting a better air flow through the house with the humidifyer set up removed, why not just try turning the nib on your new unit down to a lower temp as well as leaving off the humidifyer set up? .

I think you'd get to keep that better flow, it would probably be more fuel efficient with a lower operating temp going through your furnace, and it's not good to activate a limit control like you were on an ongoing basis. Those limits are only designed for occaisional usage.

 

ok let me try adjusting to 80 i guess. the on switch is already at 150 and the limit 200.

what should i do if even these settings cause a short cycle?

 

They are just simply bymetal mechanical temp contols that activate two switches. If your operating furnace temp is really that low then the folks here will help you deal with that situation.
It won't hurt anything to lower that off fan nib. Too low and the fan won't ever shut off but the correction for that is just to readjust the nib back up a bit higher.
Once you get the fan to stay on through the whole heating cycle and have it continue to run as long as the furnace can supply usable hot air out of the registers, then tell us what the normal operating temp is on the fan/limit control while the gas is burning.

 

I turned it down to 80 and I also left only a crack open on a register in the 2nd floor bathroom. This vent is a direct path to the furnace and it gets the most heat and the heat continues even after the fan has stopped.

I am happy to report it has stabilized. It's running at 100 degrees on the dial. What is the ideal number it should run at?

(thanks again you saved me lol)