About 2 years ago we had a high eff. furnance installed in the basement, the plastic pipes for intake and exhaust were routed one story above and then horizontally across a two car garage to the exterior. The pipes are about 12 feet above grade and on a west wall of the house. My question is as follows: I noted a statement by a user of this forum that these inlets and outlets should be about 2 to 3 feet above grade. Is this correct? Are our outlet/inlet in incorrectly installed. Additionally, we are in Kansas outside of Kansas City and prevailing west winds are the norm and these winds will put pressure on the exhaust pipe which is horizontal with no real cap. Does this decrease the efficiency of the furnance and explain the loud banging noise from the furnance during cold windy days? - our furnance company says it is not. (sorry that this is so long). Thanks so much.

That would be a minimum of 2 or 3 feet above grade, and that is just so that the inlet and outlet are not blocked by snow.

I don't know what causes the banging in the furnace, but I think you could put an elbow on the pips and then a short length of pipe aiming down, cut off at a 45-degree angle, with the long side outward, at least on the exhaust. The inlet is probably fine as it is. But, before you do anything like this, read very carefully the furnace manufacturer's installation instructions, to see what they say about how the exhaust is to be piped. If you don't have them, they are probably available online from the manufacturer's web site.

To Richard H.

Thanks so much for the suggestion. I have found the installation guidelines and they do not address the banging issue (as we might have suspected), but I will check into your suggestions about the termination. Yes, you were correct about the wall installation. Higher heights are desirable as are vertical stacks. Again, thanks so much for the suggestions.

What brand is the furnace?
The banging noise you hear, Does it happen when the furnace starts up?
If so the noise you hear is the oil canning of the ducts. What often happens is the return duct on the furnace is undersized or the return duct is being blocked either from dirty filters, or a host of other things. When the furnace starts to run the main blower comes on at the same time. Unlike the lower efficency units that do not turn on the blower until the furnace comes up in temps. When the blower comes on it causes a suction on the return duct which in turn collapes the duct causing the noise you hear. When the furnace stops the duct returns to its origional shape thus causing the noise you hear.
To test this theory you simply need to take off the blower door on the bottom of the furnace. Hold the safety switch on to simulate the door being in place. Then have someone turn up the Thermostat and listen for the noise. If it does not happen your halfway home.
Then put the blower door back on and watch the ducts that return the air back to the furnace. You will see the duct moving as the lower air pressure created when the furnace starts.
If you have checked the ducts and they are not blocked you can simply purchase small angle steel brackets at the local hardware store or big box store and fasten them onto the metal duct where it appears to have moved.

The exhaust ducts location is critical for only a few reasons.
It should not be located near a window that opens. As there is a chance that the combustion gas can re-enter the home if the window is open for fresh air. You should see that on the instructions.
It should be discharging at least 12 inches above the natural snow fall in your region. The higher the better. 2 to 3 feet are a rule of thumb.
As far as worrying about being on the wrong side of the house. If the furnace has been working its not a concern. I do not think I have ever heard of a furnace not working because of wind blowing into the ehaust vent.

The only thing that is critical on the cap is that it does not have any wire mesh covering it where water can stick to. And that the pipe does not extend to far out into the outside air.
The reason for this condensing furnaces do just that. Condense. They squeeze the latent heat out of the flue gasses so well they cause condensation to form. This is why the pipes should be pitched all the way back to the furnace. When you see the furnace run you see a lot of vapor exiting during the colder days. This moisture oftentimes can collect on any grills that are on the exit area of the pipe. When the furnace stops running the moisture freezes on these surfaces and begins to build up. Over a period of time a block of ice forms and the furnace does not turn on.
So this is why you do not have any sort of cap on the end of the pipe.

To: Home Care Club

Thanks so much for your suggestions. We have a high efficiency Lennox 61mpu600-135(135,000 btu signature series furnance). The banging noise seems to happen randomly, so I will investigate further. I have brought home a digital sound recorder and will place this on the furnance to record the bangs. We have a 10 year warranty on the unit. Oil canning seems to be a best suggestion. I had our furnance company out to look and they suggested that it was an oil canning related to the humidifier, they said they fixed it. I am imagining that the number of booms increases with wind speed. Before bothering with the digital sound recorder I will try the experiment you suggested. Possibly, I am only sensitive to the wind speed during extremely cold weather and that this same cold weather is causing the ducting to oil can as you suggested.

Last year our furnance stopped working because birds had built a nest in the intake pipe and the furnance would not ignite. I have solved that problem without interfering with intake or outflow. However, that is what raised the issue of whether the system was shutting down because of low pressures caused by the wind flowing between the houses.

The exhaust and intake are part of a plastic end fitting designed for these installations. Think of a oblong circle where the intake is on the backside of the circle and the exhaust is on the fronside in the center. There is a plastic "dinner-plate-like" part with a hole in the middle that exhausts the pipe and under the plate is the intake.

Possibly, I have become paranoid about these sounds, particularly since our heating usage has increased 50% and our bills even more so, even after controlling for heating degree days. I have imagined that the unit has cycled off and on inefficiently. Possibly, professional such as yourselves believe this is extremely unlikely or even if it occurred our bills would not be so adversely affected.

No matter whether the bill is high or not, I am worried about the mechanical consequences of the loud bang.

I will investigate this further and thanks again for your suggestions. I will post results so that you might have stories about the paranoid oil canning homeowner.

SteveD

If the furnace is shutting down because of air pressure on the flue pipes exiting on side of house you would know this. The Lennox units as well as many of the other units on the market have computer boards in their makeup. These smart furnaces have indicator lights and trip devices that are set off when something is not right. With over-pressure on a flue exhaust pipe a special safety switch would be tripped and or a light will blink or turn on or off telling the mechanic who services the unit what happened. If the trouble light or switch tells him that the flue was blocked or over pressured in the case of air on outside blowing against pipe he or she would know that and make the necessary correction.
Other reasons for these high tech units to fail can be simply to much or to little gas pressure. however none of these issues your explaining is something to worry about unless it happens all the time.

The banging sound your hearing again is nothing to worry about unless your babysitter has been watching to many horror flicks on the TV But simply turning the fan switch on and off and allowing the fan to start and stop completely you should be able to find the duct movement and correct it with a simple metal angle bracket with a few screws.

In regards to the higher heating usage. 50% does sound like a lot. But take into account the weather and cost of fuel and that may answer some questions.

Although we heat with gas, our electrical bill went from $97 in October to $168 for December. Because of the additional amount of furnace operation. So your not alone with the higher fuel and energy costs.

Be sure that your humidifier is working correctly and that its clean. Adding additional moisture into the air in a home in the winter will lower your heating costs.