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This article details the changes needed to water heater venting when a High-E Furnace is installed in an existing home.  HomeProPlumber provides full service plumbing maintenance, repairs and replacements for every plumbing component in your home. We sell and install Rheem Professional Series gas & electric water heaters, and tankless water heaters.  We are near your home in Plano, Allen, Frisco, and McKinney.  We service all homes in southern Collin and Denton Counties with no additional travel-charges.

HomeProPlumber in Plano, Texas provides maintenance & repairs for all brands of Central A/C, Gas & Electric Furnace, and Heat Pumps.  Additionally we sell and install new HVAC Systems from American Standard (same company as Trane), Ameristar (same company as American Standard) and Coleman HVAC (same company as York HVAC).

Call us today to discuss any concerns or problems you have with your HVAC System or Plumbing.  We will arrange an appointment at your convenience and offer 24/7 Emergency Service  

Gas Water Heater Venting When Installing A

High Efficiency Gas Furnace In An Existing Home

This article addresses the changes required to existing water heater venting when a High-Efficiency furnace is installed in an existing home that had a standard-efficiency furnace and water heater if they shared the same exhaust venting.  Many homes are built with the water heater and furnace sharing the same exhaust vent.  This practice is common with standard efficiency (80%) furnaces.  When installed correctly, this venting arrangement works with an 80% gas furnace (or less than 80%) + gas water heater.  The photo below shows typical combined furnace + water heater venting.  

When installing a High-Efficiency Furnace, the existing shared vent will not work for only the water heater because the vent is too large for the water heater’s exhaust to to warm the pipe enough so it rises safely out of the home.

The old vent pipe is too large because it served both the furnace and water heater.  High-E Furnaces have totally separate venting. When a standard-efficiency furnace is replaced with a high-efficiency the existing vent pipe must be replaced with the correct vent size for only the water heater (it will be smaller).   This ensures the water heater can heat the vent pipe enough to get exhaust gasses to rise.

This type of pipe is called “B Vent”.  Type B gas vent pipe has  a smaller pipe inside a larger pipe (also know as double wall pipe) for insulation and safety.  This ensures the outside pipe is cooler than the inner pipe.   The airspace between the inner & outer pipes provides insulation against heat loss (from the inner pipe) as flue gasses are rising out of the home.

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You Can See Both The Inner & Outer Pipes In The B-Vent Pipe Photo Shown Above

 

Gas Water Heaters Come In Different Sizes (gallons)

THE VENT PIPE MUST BE THE SAME DIAMETER AS THE WATER HEATER’S DRAFT HOOD. 

The maximum dimension of the (water heater venting only) vent pipe is determined by;

1. How long the vent pipe is.

2. Water Heater size (in gallons).  Typically, if the existing vent (that served both furnace & water heater) is larger than 4 inches, so a smaller vent pipe must be installed for only the water heater.

3. Because the new vent pipe is smaller, it can often be installed inside the old vent pipe.  

Image Source: Dreamstime 40163150

High-E Furnaces have separate venting (see white plastic pipes coming from top of furnace). One pipe provides combustion-air coming in & 2nd pipe vents exhaust gases out.  

What Happens If A The Existing Vent Pipe Is Not Replaced?

With a vent pipe that is too large, the water heater does not produce enough heat get exhaust gases to rise out of the home.  In this case, the exhaust gases backdraft into the home.  Backdrafting means the exhaust gasses move downward in the exhaust pipe.  Then the gasses end up inside the home.   These exhaust gases contain carbon monoxide which will make occupants sick in smaller concentrations, and can kill in large enough concentrations.

How To Know A Gas Water Heater Is Venting Safely?

TO TEST FOR PROPER WATER HEATER VENTING:

• If water heater and a gas furnace share the same vent, reduce the thermostat setting for the furnace so it does not run during the test.
• Run enough hot water for the water heater start heating.
• Allow water heater to run for 10 minutes.
• Be sure all windows & doors are closed & locked.
• Close fireplace damper(s).
• Turn all kitchen & bathroom exhaust vents on
• Turn clothes dryer on

With this test, even with everything running (that pulls air from the house)  a properly vented gas water heater will not backdraft.

Note: You Can See Backdrafting Using An Incense Stick.  While lighted, incense sticks produce a scented smoke.

  

Click On Photo To: See, View Details, or Purchase the item from Amazon.com  

Click On Arrow Inside The Photo To See A Backdrafting Water Heater (as it’s happening). 

Image Source: YouTube

Image Source: YouTube Embedded Video

SUMMARY:

This article provides valuable information regarding why an existing shared (by furnace + water heater) vent pipe must be installed when installing a High-E Furnace.  This is because the vent will now be used by only the water heater.

Most homes have a shared vent (serving both the furnace + water heater) when the furnace efficiency is up to 80% (which is today’s standard efficiency gas furnace).  A High-E furnace has separate venting.  So, the existing vent pipe is too large for proper venting and must be replaced with one of a smaller dimension.  This ensures the water heater’s exhaust gases are warm enough to rise out of the home safely.   If this is not done, the water heater will likely backdraft — allowing exhaust gases will come into the home.

HomeProPlumber 

HomeProPlumber provides full service plumbing maintenance, repairs and replacements for every plumbing component in your home. We sell and install Rheem Professional Series gas & electric water heaters, and tankless water heaters.  We are near your home in Plano, Allen, Frisco, and McKinney.  We service all homes in southern Collin and Denton Counties with no additional travel-charges. HomeProPlumber in Plano, Texas provides maintenance & repairs for all brands of Central A/C, Gas & Electric Furnace, and Heat Pumps.  Additionally we sell and install new HVAC Systems from American Standard (same company as Trane), Ameristar (same company as American Standard) and Coleman HVAC (same company as York HVAC).

Call us today to discuss any concerns or problems you have with your HVAC System or Plumbing.  We will arrange an appointment at your convenience and offer 24/7 Emergency Service