TOILET VENTILATION CALCULATION

TOILET VENTILATION

Toilet ventilation has its own importance for odor control and fresh air provision.

When considering mechanical ventilation for a toilet exhaust, the most important task will be the following.

• Find out the Exhaust air flow rate.
• Exhaust air duct size (if applicable).
• Static pressure calculation for duct and duct fittings.
• Exhaust air fan capacity.
• Fresh air intake flow rate.
• Door under cut (or) door grill (or) fresh air duct.

Properly sized ventilation in airtight homes and 


apartments helps to assure healthy indoor air quality. 


Both intermittent (spot) ventilation and continuous 


(whole house) ventilation should be considered. 


Intermittent ventilation is used to exhaust sources of 


moisture and odors, while continuous ventilation is 


used to remove accumulated indoor air pollutants. 


Ventilating fans should be located near the source of 


moisture and indoor air pollutants in bathrooms, 


laundry rooms, kitchens, hobby rooms and smoking 


rooms.

1. Determine the Application

The first step when sizing for a ventilating fan is to 


determine the application. Decide whether you are 


sizing for intermittent or continuous ventilation. If 


intermittent, determine which application i.e. bathroom, 


kitchen or other. Use the following industry 


recommendations to determine Air Changes per Hour 


(ACH) for your specific application.

Intermittent (Spot) Ventilation:

The Home Ventilating Institute (HVI) recommends the 


following Air Changes per Hour (ACH):

I. Bathrooms - 8 ACH

II. Kitchens - 15 ACH

III. Other Rooms - 6 ACH

2. Calculate the Area Being Ventilated

The second step is to calculate the area being 


ventilated. Calculate square feet or cubic feet 


depending on which sizing method you choose.

Both methods, the Sizing Chart Method and the 


Performance Curve Method, follow industry standards 


and will give you similar outcomes. The Sizing Chart 


Method is easier. The Performance Curve Method is 


often preferred by engineers.

Example:

Sizing for an 8 ft x 12 ft x 8 ft ceiling bathroom using 


12-foot long, 4 inch diameter aluminum flex duct, one 


elbow, one wall cap.

Step 1: Airflow (CFM) Calculation

First calculate area in cubic feet (length x width x 


ceiling height). Then divide this number by 60 to get 


the Cubic Feet per Minute (CFM) required to replenish 




the entire air volume in one hour. Next, multiply the 




CFM value by the appropriate ACH value for the given 


application.

1a. 8 ft x 12 ft x 8 ft = 768 cubic feet

1b. 768/60 = 12.8 CFM value

1c. 12.8 x 8 ACH

 102 CFM for intermittent bathroom ventilation

Step 2. Static Pressure (Resistance) Calculation

The Static Pressure calculation provides EDL and 






adjusts for airflow resistance caused by duct material, 




elbows, and terminations devices.

2a. 12 ft flex aluminum duct x 1.25 = 15 feet EDL

2b. One elbow equals 15 feet EDL

2c. One roof jack equals 30 feet EDL

15 + 15 + 30 = 60 feet total EDL.

3. Measure the Equivalent Duct Length (EDL)

The third step is to measure the Equivalent Duct Length 


of the planned duct run. This requires a basic 


understanding of static pressure caused by a duct run 


design and its components.

Static Pressure and Duct Run:

A ventilating fan must overcome resistance when 


pushing air from the inlet, through the duct, to the 


outside of the building. This resistance is known as 


static pressure. The amount of static pressure depends 


on the duct length, type of duct, elbows and the roof 


jack or wall cap.

Equivalent Duct Length (EDL): 


Static pressure in a typical duct run is caused by the 


type of duct material, elbows, exterior wall cap, etc. 




The table below shows the standard values for duct 


components. The EDL chart allows you to calculate the 


equivalent straight duct length in order to overcome 


static pressure caused by each component in a duct 


run.

Equivalent Duct Length
Duct Diameter
Duct	Smooth Metal	Same as measured duct length
Material	Flex Aluminum	1.25 x duct length	1.25 X duct length	1.5 X duct length	1.5 X duct length
	Insulated Flex	1.5 X duct length	1.5 X duct length	1.75 X duct length	1.75 X duct length
Terminal	Wall Cap	30 feet	30 feet	40 feet	40 feet
Device	Roof Jack	30 feet	30 feet	40 feet	40 feet
Elbow	Adjustable	15 feet	15 feet	20 feet	20 feet