Author Topic: Venting High Efficiency Condensating Furnace  (Read 2931 times)

Offline lymer

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Venting High Efficiency Condensating Furnace
« on: October 18, 2015, 09:19:59 AM »
Just had a New Goodman Furnace installed (GMVC96)

Two questions:

One:  It is a little noiser then I imagined.  It seems to be at the start up and then quiets down a short time later.  But at the start up I can only describe the sound as a hollow harmonic sound that seems to be synchronized to the blower motor coming on.  Then after a short time it runs normal and fairly quiet, I guess. This furnace is replacing a 25 year old mid-efficiency single stage so not sure what to expect in terms of noise for a two stage, ECM variable motor noise levels kind of thing .  After that short term I mentioned I would describe the running decibel as slightly quieter then my old unit, but that harmonic, hollow sound at start up seems a little louder then my old unit at start up.

Two:
I am unsure if the angle to my wall of the exhaust PVC pipe leaving my home is OK.  It may be an issue or it may not.  It angles slightly back towards the house (Approx 10 to 15 degrees).   With the condensation building over time this winter I am concerned that the water will run back inside the PVC pipe and pool.  This pooling of water could perhaps freeze inside the pipe throughout the winter and form an ice blockage.  My house wall is North facing and the coldest side of my home.  If this happens it could block the exhaust flow and essentially shut down the furnace.  This might be a stupid question but I just had to ask.  I would add pictures but this Newb seems to be having difficulties with that


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Re: Venting High Efficiency Condensating Furnace
« Reply #1 on: October 18, 2015, 02:12:51 PM »
Without hearing the noise it's hard to say if it's normal.  The inducer motor is likely the source of the noise and may need to be replaced.

The venting should slope downward towards the furnace about 1/4" per foot of venting.  The condesation, inside the vent, has to travel back to the furnace and out the furnaces drain line.

When you post click Additional Options then click Choose File to post a picture.

Offline lymer

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Re: Venting High Efficiency Condensating Furnace
« Reply #2 on: October 18, 2015, 04:30:46 PM »
Thanks for the help here are the attachments showing the angle and the basic install of my vents.  You say this angle back towards the furnace is the way to install so that the condensation rolls back and then drains through the drain tubes at the bottom of the furnace.

If I understand you correctly

Offline walker

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Re: Venting High Efficiency Condensating Furnace
« Reply #3 on: October 19, 2015, 09:45:35 AM »
it probably sounds louder at start up because it fires up on high fire then after about 20-30 seconds it will go back down to low fire and it will quiet down.  Let it run for another 5-12 minutes and you'll hear it kick back in to high fire again and it will then again sound louder.

As far as the venting goes that looks fine to me.  You could add some insulation to it, but in my opinion it doesn't look long enough to warrant that.

Offline Porcupinepuffer

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Re: Venting High Efficiency Condensating Furnace
« Reply #4 on: October 19, 2015, 03:50:25 PM »
The vents leaving the house definitely has at least 1/4" per foot, which is correct. You won't have condensation issues.

On a slightly related note, the a/c condenser could have been installed a bit cleaner with the linesets. I always try and tuck in the liquid line tight with the vapor line. I would have did everything in my power to keep the linesets at the back of the a/c. I could be wrong since I'm more accustomed to Carrier units, where both lines terminate on the corner on an angle, and I can always make them connect at the back.

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Re: Venting High Efficiency Condensating Furnace
« Reply #5 on: October 19, 2015, 04:25:18 PM »
I see now Lymer is concerned with the angle of the outside vent.  I agree it's a little excessive.  It could certainly allow snow and rain entry into the vent.  With the new Lennox furnaces I know this could cause a problem, as the drain lines attached to the ventor motor coupling are useless at collecting anything but a small drop of water, and any excess moisture would collect inside the bottom of the ventor motor and cause a pressure switch lockout.  I'm not sure if the same thing could happen to this Goodman furnace.  According to the GMVC96 manual you could install a tee instead of an elbow, on the end of the vent pipe, which may prevent elements from entering the vent pipe as easily.

Offline lymer

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Re: Venting High Efficiency Condensating Furnace
« Reply #6 on: October 19, 2015, 05:20:20 PM »
So if I wanted you think I could cut off the elbow and fit it with a tee.  I can certainly see how this might help keep excess moisture from snow and rain water from collecting inside the bottom of the furnace.  So the GMVC96 allows for a Tee-fitting, does that mean I should be OK to simply cut off the Elbow and install the Tee in its place.  I will lose a little height but not much. should still be within code I imagine.

Porcupinepuffer:  I agree with your thoughts on my A/C condenser needing to be installed with cleaner linesets. When I brought that point up with my contractor during the install he said, this was the easiest way to install the unit for future maintenance and service down the road.  If you look at the picture of my unit it is hard for me to disagree.  As you turn the unit to change the line-in orientation you are either tight to the wall or tight against my side fence.  He was dealing with an existing hole in my wall from an older A/C unit I replaced.  I agree though that for the number of times it gets serviced (I hope) my visual aesthetics summer in and summer out should have taken some precedent over a tight service spot

Offline Sergroum

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Re: Venting High Efficiency Condensating Furnace
« Reply #7 on: October 25, 2015, 01:04:51 AM »
It may also be that your ventor motor kicks into higher speeds during calibration, which could cause excessive noise, but once the calibration is finished, it would run quieter.