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Old 07-20-2018, 12:42 AM   #46
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Re: Replacing my HVAC unit


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Originally Posted by user_12345a View Post
It's easier for the contractor to connect an existing b-vent or chimney pipe than run now pvc pipes.
My current 80% gas furnace utilize one metal vent for exhaust. Do you happen to know why 90%+ gas furnace switch to PVC as the material for piping/venting?
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Old 07-20-2018, 01:35 AM   #47
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Re: Replacing my HVAC unit


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Originally Posted by 012abc View Post
My current 80% gas furnace utilize one metal vent for exhaust. Do you happen to know why 90%+ gas furnace switch to PVC as the material for piping/venting?
the exhaust from a condensing furnace is 100% relative humidity, so the inside of the pipes get wet. I assume it's because what's the cheapest material that's readily available, handles wet well and is easily made gas tight? PVC pipe. you could do it with stainless or copper pipe perhaps, but PVC is way cheaper.
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Old 07-20-2018, 04:45 AM   #48
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Re: Replacing my HVAC unit


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Originally Posted by 012abc View Post
My current 80% gas furnace utilize one metal vent for exhaust. Do you happen to know why 90%+ gas furnace switch to PVC as the material for piping/venting?

Because the PH of the condensed moisture would eat through the galvanized metal pipe, and allow CO into the home.
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Old 07-20-2018, 05:21 AM   #49
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Re: Replacing my HVAC unit


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Because the PH of the condensed moisture would eat through the galvanized metal pipe, and allow CO into the home.
CO = carbon monoxide?

So CO is the bi-product of any type of gas furnace (both 80% and 90%+)? Since 80% gas furnance has no condensed moisture, there's no need to worry about any sort of thing to eat through the galvanized metal pipe?
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Old 07-20-2018, 05:48 AM   #50
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Re: Replacing my HVAC unit


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Originally Posted by 012abc View Post
CO = carbon monoxide?


Yes.


So CO is the bi-product of any type of gas furnace (both 80% and 90%+)?



Yes.



Since 80% gas furnance has no condensed moisture, there's no need to worry about any sort of thing to eat through the galvanized metal pipe?

Not as much worry, as long as the 80%er and the chimney/flue is working/operating correctly.
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Old 07-20-2018, 10:14 AM   #51
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Re: Replacing my HVAC unit


To add to that, the exhaust of a condensing furnace is too cool to rise up through the chimney/b-vent a mid or conventional (<80%) furnace uses.

The mid, despite using a fan to induce a draft in the heat exchanger normally has the exhaust side run under negative pressure when vented into a chimney or b-vent, condensing is positive.

You may notice your existing venting isn't sealed, the pipes are screwed together and that's it. The negative pressure means exhaust can't leak out, only a tiny amount of indoor air can leak in.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 07-30-2018, 08:52 AM   #52
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Re: Replacing my HVAC unit


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...
The filter right before the blower.

I currently have a 1" air filter sitting right before the air get suck into the blower. For the purpose of air cleanliness, is there a point to ask the HVAC people to install a mechanism so I can use thicker air filter? Say using a 4" air filter.
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Old 07-30-2018, 11:15 AM   #53
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Re: Replacing my HVAC unit


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Originally Posted by 012abc View Post
The filter right before the blower.

I currently have a 1" air filter sitting right before the air get suck into the blower. For the purpose of air cleanliness, is there a point to ask the HVAC people to install a mechanism so I can use thicker air filter? Say using a 4" air filter.
Yes.
as an example:
https://www.acwholesalers.com/Honeyw...xoCHyUQAvD_BwE

you will need your HVAC contractor to re-work the duct (I recommend turning vanes if things are tight) so that filter box fits between the return duct and the furnace. then the 1" air filter gets thrown out.
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