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Selecting the correct fan and size for a bathroom.


Step 1: Pick a fan that will provide at least 8 air changes per hour. You can use our bathroom system builder/calculator for this or the following formula:

- Add the volumes of the bathroom(s) to be ventilated
where Volume = length x width x height (bath1) + length x width x height (bath2) etc. If you are venting a single bathroom using the fan, then calculate the volume for only that bathroom.
- Required air flow in CFM (cubic feet per minute ) = Volume / 7.5
This is the minimum air flow required to achieve 8 air changes per hour - more is usually better.

We recommend that you provide a minimum of 75 CFM for even the smallest bathrooms. When ventilating very large bathrooms, the required airflow may be reduced if the grilles can be placed near the sources of moisture and smells.

Step 2: Select fan type and installation location.

Fantech fans are available for mounting on the roof, on the wall, or attic (in-line) mounted. For applications in which the attic is easily accessible, we would recommend the FG or FR series in-line fans.


FR Series In-Line Fans From Fantech
FG Series In-Line Fans From Fantech
FG (metal cased) Series Kits

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This series is the most commonly used for the following reasons:
- multiple fans ranging from 122 to 650 nominal CFM (see notes below on actual fan flow rates)
- great performance to price ratio
- available in convenient, economical kit form including grilles, "Y" fittings, etc.
- fully speed controllable
- 5 year warranty

The next most popular fan is the RVF series. This fan mounts on an outside wall.

RVF Series Fans From Fantech

We would suggest this fan for:
- venting first floor baths in 2 story houses
- houses where the attic is otherwise inaccessible
There are 5 fans ranging from 124 to 435 CFM in this series and all are fully speed controllable.

For roof mounted fans, use the RE series from Fantech. This fan is designed for installation either on shingles (RE) or on flat roofs (REC) with the use of a curb.

RE/REC Series Fans From Fantech

There are multiple fans to choose from ranging from 125 to 1080 CFM and all are fully speed controllable.

The last type is the CVS series from Fantech. It is basically a "fan in a box" with 3 to 4 ports on the side. This fan is great for tight spots and/or when multiple venting points are required.

CVS Series Fans From Fantech

There are 3 fans to choose from ranging from 250 to 405 CFM and all are fully speed controllable.

Once you have selected the fan type and decided on an approximate layout for the ducting, you can use our bathroom system builder/calculator to get the actual airflow for your own system. Without getting too technical, the nominal airflow for the fan is the amount of air the fan will blow without any duct attached. Of course, adding duct, elbows, grilles, roof caps, etc. will all act to restrict the flow. Most applications will have between 0.2 and 0.4 inches of water column resistance. You can look this value up in the performance table that is shown for every fan. This will give you the actual CFM that you can expect from your fan, not just a nominal CFM.


Additional Notes and Tips:
- suggested maximum airflow for Fantech exhaust grills is: 4" - 100CFM, 5" - 125 CFM, 6" - 150 CFM, 8" - 200 CFM
- use flexible insulating ducting to limit noise and condensation
- use 8 feet or more of the insulated ductwork between the grille and the fan to maximize acustical benefits
- make sure that you hang the duct so that no valleys are created -- condensation can pool in the valleys, potentially blocking the air flow
- always use a backdraft damper to prevent drafts

More Links:
- Fantech Speed Controls and Timers
- Fantech Grilles
- Fantech Flexible Insulated Duct
- All Fantech Products


As always, if you would like to ask more questions about this or other technical topics give us a call at 877-711-4822 - 9-5 PST. Live people for technical and sales support - an Internet first!

Pictures and images courtesy of Fantech.