How do I calculate what size ventilator I need for my attic?
Use the calculator on the Broan.com website, or follow the example below:
How much free area air intake do I need in the attic for the ventilator to work properly?
- Calculate the volume of your attic, in cubic feet, depending on the style of your home’s roof
Attic Volume for Gable Roof
Volume = Length x Width x Height x 1/2
Attic Volume for Hip Roof
Volume = Length x Width x Height x 1/3
- Attic Volume x 10 Air Changes per Hour = Total Cubic Feet per Hour of ventilation recommended
- Total Cubic Feet per Hour ÷ 60 Minutes/Hour = Cubic Feet Per Minute of ventilation recommended. Many Attic Ventilator manufacturers provide ratings for their products’ Cubic Feet per Minute (CFM)
Example: Average Gable Attic Volume = 58.75’ x 29’ x 7.25’ x ½ = 6,176 Cubic Feet
6,176 Cubic Feet x 10 Air Changes/Hour = 61,760 Cubic Feet/Hour ÷ 60 Min/Hour = 1,029 CFM
Replacement air is drawn through vents in your soffit. To determine the minimum soffit vent area required (in square inches) multiply the total CFM of your powered ventilator(s) by 0.48. This number is the total square inches of soffit venting required by your powered ventilator(s).
Example: 1,029 CFM x 0.48 = 494 Square Inches of soffit vent area recommended.
How do I calculate the existing free air in my attic?
If you have eve vents or gable vents multiply the length by width of each one. This will give you the square inches (if the opening is covered with screen divide by 2). The net free area may be stamped in the frame on the vent. Add up all the totals from all of the vents to get your total existing free air area.
What if I do not have enough free air area in my attic?
We recommend adding additional free air area to insure that your Attic Ventilator works at optimal efficiency.
At what temperature should the thermostat of the Attic Ventilator be set?
This varies depending on the climate of your home and the sun exposure of your roof. A starting point to determine an on/off temperature is to measure the summertime temperature of the attic in the evening, when there is no sun. Use this temperature as a baseline; when the temperature gets warmer, the ventilator should operate.
Can I paint the dome on my attic ventilator? If so, what kind of paint do I use?
Yes. The dome may be painted using a normal water base exterior house paint.
Can a variable speed control switch be used with an attic ventilator?
Yes, Model 72W or 72V variable speed controls may be used with the Models 350BK, 350br, 353, 35316, 355BK, 355BR and 358. Do not use these controls with Models 356BK or 356BR.
Can a gable ventilator be installed on a roof?
No. Gable Ventilators are designed to be installed on vertical locations.
Can an attic ventilator be installed on a vertical surface?
No, except for Gable Mount styles, Broan attic ventilators are to be installed on horizontal or sloped surfaces.
Can an attic ventilator be installed on a flat roof?
Yes. Note that a curb will need to be built so that the housing is higher and snow and water levels would not affect product performance.
Can I install a dehumidistat on an attic ventilator?
Yes. Use model DH100W.
Why would I need an ERV or an HRV for my home?
The air circulation within your home may be good, but more likely the air quality is poor. It's damp, stuffy, or making you sick. Replacing appliances such as a furnace or water heater, installing new windows or adding siding to a home changes the air leakage rate. Any improvements made to a home that reduces airflow in a house may result in insufficient natural ventilation. Excess moisture destroys your windows and building structure. Mold, mildew, carbon monoxide and chemical pollutants are harmful to human health. You need to build tight, but more important, ventilate right.
Would I be able to improve my air quality with just a ventilator?
Healthy indoor air requires you add a mixture of regular fresh outdoor air. Tighter building construction causes negative pressure when bath fans, kitchen range vents, clothes dryers and other exhaust equipment are in use. Your vent fans suffer. They will not be effective and motors will wear out more quickly.
Why is an HRV or ERV system better than a regular ventilator?
Ventilators do not recover the energy (heat or cooler temperature) from the air being exhausted. An ERV and HRV unit transfers the temperature to the fresh air being drawn into the home. Reheating or cooling costs become minimal in comparison to heating or cooling air being drawn in through cracks and leaks in your building structure.
Must I also install bath fans if I choose to install an IAQ system?
An IAQ vent system cannot be as effective if the high levels of humidity generated by today's shower and tub systems is allowed to dissipate throughout the entire house. It should be removed at the source by running a bathroom exhaust fan for 20-30 minutes after each shower. Your bathrooms should be properly measured and fans for each room must be chosen with proper CFM (Cubic Feet of air per Minute). Then the house's general ventilating system can control the moisture.
Can I ventilate my bath fans through an IAQ system's ductwork?
It is not recommended that you do this. When an IAQ system has been properly sized and balanced, any vent fan that operates during operation of the IAQ will unbalance that system, rendering it ineffective. The high humidity from the bathroom, along with any odors, may be circulated throughout the rest of the house.
How much fresh air is needed in a home?
A vent system designed to provide fresh air must provide approximately one-third (0.35) air changes per hour.
To calculate the required minimum CFM, divide the square footage of your house by 20, or consult a qualified HVAC contractor to properly size your building.
Who installs IAQ equipment?
Generally it should be installed where your furnace and A/C is because proper sizing and balancing of the system is critical. The unit must be installed in areas that do not get below 40°F. A floor or pipe drain must be available.
What types of controls are available to operate the IAQ equipment?
Low voltage wiring (4-conductor telephone-type cable) is required to install the humidity controls, which activate and operate the ventilation equipment. The ERV must have one of the Central controls. The VT3W (our DETECTOR model) activates the ERV by sensing pollutants (not humidity). There are also 20 minute push-button timers available to activate the units for short intervals rather than operating in a "constant on" mode.
Where is an ERV or HRV installed?
Because the unit is equipped with drains to eliminate humidity from the air, the unit must be installed in an area that does not get below 40° F. A floor or pipe drain must be provided.
Can I use a BROAN-NuTone residential ERV or HRV (100 or 200) to ventilate my pool or spa areas?
No. The units are not equipped to handle the high humidity or chemical laden air generated within such an extreme situation. There is a special HRV700 in the line which accommodates that need for ventilation.
Can I wire my IAQ equipment to my furnace so it only runs when my furnace is running?
No. It is not possible to have your furnace turn your ventilator on due to the electronic circuitry. However, it is possible to wire just your furnace blower to operate while your ventilator is running so that the most effective ventilation of your whole house is possible. If you are in the habit of closing bedroom doors or other rooms you may have "dead air pockets" in your home. The furnace blower helps the fresh, dry air reach the rooms farthest from the ventilator.
Why must I have a balanced ventilation system?
Recent studies show that natural ventilation (leaks and cracks) does not provide adequate fresh air into houses. Energy efficient construction has challenged us to overcome the bad health effects and damaging humidity that tightly constructed buildings have caused. Natural ventilation does not provide adequate ventilation to control these contaminants.
What type of ducting does the equipment require?
Your system can be direct-ducted. That is, an independent ducting system can be installed in new construction. This may not work well in old construction. Your unit can be installed in your existing forced air furnace duct, which simplifies the installation in old construction. Both types of installation require a 6" inlet and a 6" exhaust port.
What is the difference between an HRV and an ERV? Which should I choose for my home?
In colder climates, where home heating is essential, the Heat Recovery Ventilator (HRV) is the proper choice.
The HRV keeps the home supplied with a steady flow of fresh outdoor air. As stale, warm air is expelled, the heat recovery core warms the incoming fresh, colder air before it is distributed throughout the home.
The result is a constant supply of fresh air, no uncomfortable drafts and greater comfort. In addition to heat recovery and improved air quality, the HRV provides necessary ventilation while controlling excess humidity.
Energy Recovery Ventilator (ERV): Ideal for warmer climates and high-humidity environments.
Even though the energy recovery ventilator (ERV) is suitable for colder climates, it is usually associated with warmer climate homes where humidity control is important.
The ERV recovers heat; however, it also recovers the energy trapped in moisture, which greatly improves the overall recovery efficiency.
The ERV process is as follows: In humid climates and air conditioned homes, when it is more humid outside than inside, the ERV limits the amount of moisture coming into your home.
In dry climates and humidified homes, when the humidity level is reversed, the ERV limits the amount of moisture expelled from your home.