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  #1  
Old 4/20/12, 8:55 AM
Joshua L. Frederick Joshua L. Frederick is online now
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Default High efficiency furnace vent clearances & insulation

What are the ideal/proper clearances between intake and water heater B-vent at the rooftop? Additionally, for those of you in "cold" areas: Do you report the lack of insulation of high efficiency furnace exhaust piping through the attic (2nd pic - PVC)??


Thanks in advance.
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high-efficiency-furnace-vent-clearances-and-insulation-img_0267.jpg   high-efficiency-furnace-vent-clearances-and-insulation-img_0317.jpg  
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  #2  
Old 4/20/12, 10:12 AM
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sgoguen sgoguen is offline
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Default Re: High efficiency furnace vent clearances & insulation

I dont its pvc and the exhaust is already cool to the touch, although i have never seen one go through a roof before. Wouldnt the condensation just run back into the unit?



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Old 4/20/12, 12:27 PM
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KEVIN WOOD, CMI KEVIN WOOD, CMI is online now
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Default Re: High efficiency furnace vent clearances & insulation

Many are designed this way as condensing furnaces work on same principle. We do not insulate them in the attic but we insulate the ones that run out the side of the home if there is exposure more than regular. Each manufacture has different requirements so it is always a good idea to check with them for installation.
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Old 4/20/12, 3:21 PM
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Default Re: High efficiency furnace vent clearances & insulation

Good advice Kevin. But if all else fails you can always wrap your lips around it and take a drag...happy 420 everyone!



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  #5  
Old 4/20/12, 4:47 PM
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Default Re: High efficiency furnace vent clearances & insulation

Quote:
Originally Posted by sgoguen View Post
I dont its pvc and the exhaust is already cool to the touch, although i have never seen one go through a roof before. Wouldnt the condensation just run back into the unit?
Not if frozen (it needs insulation,we just had a long talk with a HVAC guy last night on this.
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  #6  
Old 4/20/12, 4:48 PM
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Default Re: High efficiency furnace vent clearances & insulation

Quote:
Originally Posted by kwood View Post
Many are designed this way as condensing furnaces work on same principle. We do not insulate them in the attic but we insulate the ones that run out the side of the home if there is exposure more than regular. Each manufacture has different requirements so it is always a good idea to check with them for installation.
Your attic should be same temp as outside .
Do you run drains outside?
You can die from a blocked sch 40 exhaust.
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Old 4/20/12, 5:01 PM
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KEVIN WOOD, CMI KEVIN WOOD, CMI is online now
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Default Re: High efficiency furnace vent clearances & insulation

I am not saying I agree with it Bob. I still know that it is not required. As far as the comment of the attic being as cold as outside. No way!
I think you might be forgetting a foundamental of condensing furnaces, a large portion of the moisture is removed by the 2nd heat exchanger and it goes down a drain not up the stack.

Last edited by kwood; 4/20/12 at 5:04 PM..
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Old 4/20/12, 5:04 PM
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Default Re: High efficiency furnace vent clearances & insulation

Quote:
Originally Posted by kwood View Post
I am not saying I agree with it Bob. I still know that it is not required. As far as the comment of the attic being as cold as outside. No way!
You need to check those manuals Kevin..here is a direct excerpt for your viewing pleasure so argue with the guys who make them but not me.LOL

Not sure what attics you are inspecting but they should be with in 4-5 degrees of outside temps so I guess you live in a tropical climate ..eh?
Please put this in your files.....

Vent Freezing Protection
When the vent pipe is exposed to temperatures
below freezing, i.e., when it passes through
unheated spaces, chimneys, etc., the pipe
must be insulated with 1/2 inch thick sponge
rubber insulation, Armafl ex-type insulation or
equivalent. Insulating pipe is important to avoid
condensate icing.
For extremely cold climates or for conditions of
short furnace cycles (i.e. set back thermostat
conditions) the last three feet of vent pipe can be
reduced one nominal pipe size provided that the
total vent length is at least 15 feet in length and
the vent is sized in accordance with the venting
requirements (Table 5) before this reduction is
applied. (Example: 3” to 2-1/2” or 2” to 1-1/2”)
Smaller vent pipes are less susceptible to freezing,
but must not be excessively restrictive.
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Old 4/20/12, 5:07 PM
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Default Re: High efficiency furnace vent clearances & insulation

The B vent termination should be 2 feet high (min)
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  #10  
Old 4/20/12, 5:10 PM
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Default Re: High efficiency furnace vent clearances & insulation

intake and exhaust should be 18 (min) to 36 inch max which is why taking air from inside is stupid and also not allowed by many manufacturers. here is a shot from my inspection 2 days ago by the way and how many things wrong do you see?high-efficiency-furnace-vent-clearances-and-insulation-cat-4-exhaust.jpg
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  #11  
Old 4/20/12, 9:11 PM
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Default Re: High efficiency furnace vent clearances & insulation

4 pictures for you Bob!
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high-efficiency-furnace-vent-clearances-and-insulation-801-cooper-rd-jan-24-2011-023.jpg   high-efficiency-furnace-vent-clearances-and-insulation-455-shannon-rd-may-4-1026.jpg   high-efficiency-furnace-vent-clearances-and-insulation-311-goulais-ave-apr-12-108.jpg   high-efficiency-furnace-vent-clearances-and-insulation-72-champagne-ave-apr-9-2012-011.jpg  

Last edited by kwood; 4/20/12 at 9:16 PM..
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Old 4/20/12, 9:16 PM
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Default Re: High efficiency furnace vent clearances & insulation

First one looks like a coupling break allowing condensate to drip onto the roof,second one shows poor flashing and third one has the intake,exhaust close together at a corner.
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Old 4/20/12, 9:23 PM
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Default Re: High efficiency furnace vent clearances & insulation

I am just pointing out that they are all wrong but no insulation in the attic was required at the time of these installs. As to requirements of new High Efficiency I am not sure why they changed if indeed they did, as I have found no troubles with non insulated in the attic or above the roof.
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  #14  
Old 4/20/12, 9:29 PM
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Default Re: High efficiency furnace vent clearances & insulation

The second picture was a very high efficient unit and the flue went through a big cold attic space. No insulationanywhere and no troubles in the attic just at the seal. Here is the picture of 50.000 BTU unit.
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  #15  
Old 4/20/12, 9:40 PM
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Default Re: High efficiency furnace vent clearances & insulation

So your point is to ignore manufacturers instructions and do it like these fine examples of workmanship.
I will be sure to write them and let them know they are stupid because Kevin found some not freezing up which he knows for a fact because he watches them every day since install.
Hey a few headaches and sick days from C/O can't be all bad.

Guess the owner and HVAC expert we had last night at the Nachi Chicago meeting was full of it so thanks for straightening me out.
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