Al’s Plumbing, Heating & A/C 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).
Al’s also provides full service plumbing maintenance, repairs and replacements for every plumbing component in your home. Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters. Al’s is near your home in Plano, Allen, and Frisco. We service all homes in southern Collin and Denton Counties with no travel charges.
Call Al’s 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.
Bath & Kitchen Venting: Use Correct Sizes To Avoid Backdrafting
What Is Backdrafting?
Backdrafting occurs when the venting of combustion-gases cannot properly occur, due to a high rate air being vented from the house through exhaust fans, fireplaces and clothes dryers. Backdrafting means combustion-gases are being pulled back into the house.
Most homes have 3 Air-Exhaust Locations. Below are ranges of venting capacities:
- Bathroom 40-450 cfm * cfm = cubic feet per minute
- Clothes Dryer 100-225 cfm
- Kitchen 160-1200 cfm
A 1993 study of several newly built energy-efficient homes found that venting airflows of 300 — 550 cfm are the range where natural-draft appliances start having backdrafting problems.* Nearly all gas water heaters are natural-draft. Older furnaces may also be natural-vent.
* SOURCE: http://inspectapedia.com/BestPractices/Backdrafting_Heating_Equipment.php
How Much Air Does A Home Leak — It Depends On When It Was Built
Up To 17 ACH 1970’s built home with no energy upgrades added * ACH = Air Changes Per Hour
Up To 7 ACH 2009 Standard for new homes
Up To 5 ACH 2012 Standard for new homes in Climate Zone – 3 / CZ-3 (DFW)
Up To 5 ACH: Energy Star Rated home in DFW / CZ-3 is — 5 Air Changes Per Hour (ACH)
THE END RESULT: The Newer A Home Is, The tighter It Is. This makes backdrafting an increasing possibility based on how recently the home was built. It’s also important to know that some new homes perform better than Energy Star standards for ACH.
Bath Venting
It’s important for Indoor-Air Quality to vent humidity from bathrooms. Excess humidity can lead to mold growth, affect your breathing, and decrease comfort inside the home. For bath vents, bigger isn’t better. A bath vent which is too large for the room’s needs can contribute to backdrafting.
Formula For Sizing A Bath Vent:
- With an 8′ ceiling, the CFM rating for your fan should be as least as high as the number of square feet in the bathroom. Bathroom vent fans are rated by the cubic feet per minute (CFM) of air they move.
Example: (5′ x 8′ = 40 sq. ft.) in the bathroom.
- If you have a higher ceiling, a larger fan would be appropriate.
Example: If the ceiling is 10 feet, add +25% more capacity (2 feet = 25% of 8 feet).
A major brand of high-capacity vents rates its capacity at 432 cfm. This vent is sized for a 432 square foot bathroom — larger than the 2-car garage on many DFW homes!
Kitchen Venting
It’s beneficial to vent cooking by-products (such as airborne grease) from the kitchen. When cooking with gas, it’s important to vent gas-combustion by-products (which likely include carbon monoxide).
But, too much of a good thing can be a bad thing. At the top of this article we listed the lower and upper limit of air removed at the 3 primary locations in a home. While bath fans are less likely to cause problems, kitchen range hoods are much more likely. In today’s luxury kitchens, it’s not uncommon to install commercial vent hood. These hoods are far too powerful for residential use.
Formula For Sizing A Kitchen Vent:
- The vent needs to remove 100 cfm of air for every 10,000 BTU’s of burner output. A typical home range has around 28,000 BTU’s of heat output (with all 4 burners running on high). For a typical kitchen range, a range vent able to move 300 cfm is correctly sized.
A commercial range hood can remove up to 1200 cfm — 4 times the air needed for a typical 4-burner gas range. The vent would accommodate 4 typical gas ranges.
Can An Oversized Kitchen Vent Be A Problem? Yes!
An oversized kitchen vent can lead to backdrafting. As defined earlier backdrafting occurs when the venting of exhaust-gases cannot properly occur due to a high rate air being vented from the house through exhaust fans, fireplaces and clothes dryers. During backdrafting, exhaust-gases are pulled back into the house.
In energy-efficient homes, with little outdoor air exchange, exhaust fans can cause the indoor air pressure to become too low, In this case backdrafting will occur at any location where outside air can be pulled into the house. The most likely point of backdrafting is gas fired water heater. In more extreme backdrafting, exhaust-gases could be pulled into the house through a standard-efficiency (80%) gas furnace (which has open venting for the burners) and through the fireplace.
This photo shows the cover of an Standard-Efficiency (80%) gas furnace. The slots in the bottom panel are open so the furnace can draw air from inside the home.
Venting Airflow From An Energy Efficient Home Can Cause Backdrafting At As Little As 300 CFM *
A 1993 study of several newly built energy-efficient homes found that venting airflows of 300 to 550 cfm depressurized the home to point that natural-draft appliances can start having backdrafting problems.* Nearly all gas water heaters are natural-draft.
* SOURCE: http://inspectapedia.com/BestPractices/Backdrafting_Heating_Equipment.php
Soot on the gas fireplace logs can be expected. Their flame is designed to burn yellow or orange so it looks more like a wood fire. A yellow flame means the combustion process is inefficient and a inefficiently burning gas flame produces soot. To ensure occupant safety, gas fireplaces must be vented to the outside and must vent properly.
Gas fireplace logs will accumulate soot. Beyond that, the air venting upward through the flue should produce little to no soot on a gas fireplace. If there is soot on the sides or back of the (gas logs) fireplace, it’s not venting properly. In this case, it may also be backdrafting due to large amounts of air being removed from the home by exhaust vents or a clothes dryer.
Ways To Protect Yourself From Backdrafting
A Carbon Monoxide detector is a great way to monitor for backdrafting.
- Install 1 in an open area near the bedrooms (like a hallway) on each level
- Install 1 near your gas water heater and furnace.
Test for backdrafting with a incense sticks. They provide enough smoke to show the direction the smoke is moving.
Gas Water Heaters Are The Most Likely To Backdraft –To Test For Proper Water Heater Venting:
- Turn down the heat at the furnace if there is a shared vent
- Close all windows and doors
- Close any fireplace dampers
- Turn on all kitchen and bathroom exhaust fans
- Turn on the clothes dryer
- Run enough hot water for the water heater start heating.
With this test, you have everything running which pulls air from the house. Even with all these things running, a properly vented gas water heater will not backdraft. If it’s backdrafting, there is more air leaving the home than entering it. You can easily test for backdrafting with an incense stick.
The video below shows backdrafting as it’s occurring. You can easily test for backdrafting with an incense stick.
Image Source: YouTube Embedded Video
Provide a fresh-air supply for your water heater and furnace. Many building codes now require this to ensure proper venting.
Provide a fresh-air supply for your fireplace. This can be done by opening the window closets to the fireplace when it’s in use.
An actively burning fireplace uses as much as 600 CFM of interior air, easily depressurizing an energy-efficient home and causing backdrafting. Where fireplaces are used in air-tight houses, outdoor-air ventilation should be increased.
Provide a fresh-air supply for your commercial-grade water heater and furnace.
Opening a window near a commercial vent in a residential kitchen provides an air supply just like for a fireplace.
Al’s Plumbing, Heating & A/C 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).
Al’s also provides full service plumbing maintenance, repairs and replacements for every plumbing component in your home. Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters. Al’s is near your home in Allen, McKinney, and Frisco. We service all homes in southern Collin and Denton Counties with no travel charges.
Call Al’s 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.