The furnace sometimes has a problem firing and the installer(not hvac) thinks it is not getting enough air to fire. It eventually does fire. He removed a plug on the side of furace (about the size of a hockey puck) to allow more air in. It seems to work better but this is not how it is supposed to work. The intake is 3" pvc, 2 elbows, 18 ft long. He also measured gas pressure at two places. He thought the gas pressure coming in may be too high(12). he adjusted the internal pressure to specs. The intake pvc is not clogged. But if you remove it at the furnace it seems to fire normally. He seems to think that removing the plug is good enough. I want to make sure this is not bad for furnace and safe to run this way. Would an adjustable gas valve fix it?
Also, the gas water heater is still vented into chimney, it is in center of house. I have a slate roof so it is difficult to access chimney. The chimney has an elevated cover.
Any suggestions are appreciated.
2007-02-17 01:58:22 · 9 answers · asked by ? 1 in Home & Garden ➔ Maintenance & Repairs
The new high effiency furnaces need to draw their combustion air from outside the house. it's all about the negative pressure like mentioned above.And also as a safety to keep the combustion sealed from the ambient air in the house.
And like redbird mentioned your intake piping may be too restrictive, and may need to be replaced with a larger diameter pipe.
But everybody has overlooked the obvious.
Have you looked at the intake pipe outside?
It could be that the exhaust and intake are too close together causing the furnace to recycle the exhaust gases.
Since there is little to no O2 left in the exhaust it can cause the symptoms you've mentioned.
The exhaust should be turned up and away from the intake or straight out from the house and the intake should be turned down, to keep them at a minimum of 18" apart.
Check your manual to find out how far apart they should be and how they should be terminated.
Is it blocked by something?
Sucked up leaves etc etc.
A couple of leaves in the pipe can restrict it just enough without making it appear blocked.
I made a service call on a furnace one night for the exact same problem as yours and found the guys 6 yr old kid had stuffed a plastic bottle down into the pipe with a stick.
Just a couple more ideas for you to look at.
2007-02-18 03:15:07 · answer #1 · answered by ELF_N_MAGIC 3 · 0⤊ 0⤋
I had to replace my furnace last year, and replaced it with an energy efficient one. When it was installed, they ran the PVC exhaust through a hole in the wall, even though the chimney was very close. When I asked about this, they told me the exhaust would be restricted by venting out the chimney. Now I have a chimney that isn't being used.
They also talked about the air inlet. The flame needs oxygen, obviously. A lot of newer homes are so well sealed, that there isn't sufficient oxygen entering the house from cracks, etc. that a supplimental pipe is needed to bring in the needed oxygen for the furnace to operate. Your intake pipe may be too long?
My house is a very old remodeled relic, so there was plenty of air leaks to the basement to supply the oxygen. He did not run a separate intake, relying on the ambient oxygen to supply the furnace. It works just fine with not one glitch.
By removing the plug, you are using the oxygen in the basement. If you have an older home like me, with air entering the basement through cracks, you won't have a problem.
If this bothers you, I suggest you call your furnace man and tell him if he can't fix it the way you want, he should call in someone with more experience. It's your money, make him do his job correctly.
2007-02-17 02:15:52 · answer #2 · answered by Bare B 6 · 0⤊ 0⤋
Furnace Combustion Air Intake
2016-11-03 02:07:38 · answer #3 · answered by carballeira 4 · 0⤊ 0⤋
It does sound like it has restriction in the inlet and exhaust lines.
The installation manual will specify what the total run (intake AND exhaust together) can be, with how many 90s, 45s, etc. If the total is too restrictive, it can have firing problems like that. Taking the plug out removes enough restriction so it will fire. That's a good test.
It needs both to be unrestricted to work right, if either one, or the combination are too restricted, it won't work right.
3" is pretty good, but check the specs in the manual, add everything up and see if it was put in right.
I don't think the gas valve is the answer.
The best reason for pulling the air in from outside is that it's not pulling already heated air out of the house and wasting it, and also because when you pull the air out of the house it puts the house under negative pressure...that air has to come from somewhere, and it will come in around your windows, doors, outlets, etc. adding to the "drafty" feeling.
2007-02-17 02:18:24 · answer #4 · answered by roadlessgraveled 4 · 0⤊ 0⤋
I have had these installed in some of my construction projects. Most brands can be installed with interior air or outside air for combustion make up air. Theoretically the use of outside air is more energy efficient in that the negative pressure created by the combustion process causes air infiltration from leaky areas like windows and doors.
As far as affecting your warranty I would read the installation manual and make certain you are not voiding it.
The week point for these furnaces are the circuit boards that act up and the condensation tubing. If the drain line clogs or freezes your furnace will not open the gas valve and then you will not have heat.
2007-02-17 02:12:58 · answer #5 · answered by paul r 2 · 0⤊ 0⤋
18" of 3" pipe is too long. The longer the run, the more restriction on the flow of air. It needs to be run in 4" and reduced to three as it enters the furnace. If the 3" run was 10" or less, you would be ok. You need to go to 4" supply piping for the combustion air. You said it works fine when you take off the pvc at the furnace. That is because you removed the restriction of air flow and it is using the air from the room you are in for combustion. Change it to 4".
2007-02-17 02:27:54 · answer #6 · answered by redbird 2 · 0⤊ 1⤋
High-efficiency furnaces burn fuel at the best efficiency, hence the name. Because of this, they are very sensitive operationally. They require a good airflow to properly burn the fuel. They typically require their own "fresh air" vent to supply the needed air flow in an un-interupted means.
If it does not have this, it can be affected by negative pressure in the home, (where the pressure is somewhat of a vacuum in relation to the outside). Negative pressure can be created by other devices such as burning fireplaces, high-capacity fans (range hoods) and even the wind blowing across the house. Significant negative pressure can cause "backdrafting" of exhaust gases (carbon monoxide) into the home.
Your installer is not giving you bad information, he is following the manufacturers recommendations. It should have been done that way in the beginning. Give him a Hi-Five for fixing this for you.
2007-02-17 02:52:29 · answer #7 · answered by Appliance Man 2 · 0⤊ 0⤋
Is it a furnace hot air or hot water boiler? And what kind is it L/P or natural? What was the gas pressure in water columns. Did the installer use a wet kit to check what kind of combustion he has. What size is the room its is L x W x H. Has the installer been to any Cetp gas classes and is he certified or licensed to do this job? How many btus is the Appl. ?
2007-02-17 02:13:58 · answer #8 · answered by Anonymous · 0⤊ 1⤋
in order for a furnace to cut in it needs cold air or fresh air to tell it that the temperature has dropped .
2007-02-17 02:07:03 · answer #9 · answered by c0mplicated_s0ul 5 · 0⤊ 2⤋