Climate and Environmental Control

PortaFab modular buildings can accommodate a wide variety of systems to control temperature, humidity, and air quality. Small, inplant offices and booths are often outfitted with wall-mounted units while larger installations typically integrate with centralized HVAC systems.

Integrated HVACIntegrated HVAC

Wall UnitWall Unit


Fan Filter UnitFan Filter Unit

Air Conditioning & HVAC Systems

Standard air conditioning options include complete HVAC systems or air conditioning only systems. Framed cutouts are available for those who want to install their own systems.

To help you estimate the properly sized unit, refer to the following chart that is based on a room with normal insulation and two person occupancy. 

Area to Be Cooled in Square Feet Approximate Cooling btu/h Required
100-150 5,000
150-250 6,000
250-300 7,000
300-350 8,000
350-400 9,000
400-450 10,000
450-550 12,000
550-700 14,000
700-1000 18,000
1000-1200 21,000
1200-1400 23,000
1400-1500 24,000
1500-2000 30,000
2000-2500 34,000
Add 500 btu/h per person over two people.
Add 4,000 btu/h if area is a kitchen.
Example: 20’ x 40’ office = 800 square feet
5 people will occupy the office

Using the chart, 18,000 btu/h are recommended + 500 btu/h for each person over two
(3 x 500 = 1,500 btu/h).

Total needed for 800 square foot office with 5 people:
18,000 + 1,500 = 19,500 btu/h

Although HVAC units are available in the above mentioned sizes, it is better to supply two units half the size located at either end of the building to provide more even distribution.

This chart is provided for ESTIMATING PURPOSES only. Individual requirements vary based on part of the country, plant heating/cooling loads, etc… If a more accurate figure is required, please consult the services of a qualified engineer.


Baseboard heaters provide a cost effective
alternative for some modular offices.

The most common way to heat a modular office is to include a combination heater/AC unit.  Baseboard heaters, however, can also be used.  To specify your heating requirements, you can estimate that you will need 7 watts of electric heat per square foot of floor space for a unit with an 8’ ceiling height. The number of watts calculated x 3.4 = total btu’s.


16’ x 16’ office = 256 square feet
256 s/f x 7 watts = 1,792 watts
1,792 watts x 3.4 = 6,092 btu/h


Standard exhaust fan.

The amount of ventilation required in an office or building is based on the application of the room as well as the number of expected occupants. For example, a smoking enclosure would require more ventilation than a regular office. The design requirements will be listed as:

Cubic Foot Requirements – A fractional formula based on .15 cubic foot requirements.


12’ x 12’ x 8’ ceiling = 1,152 cubic feet
1,152 c/f x .15 = 173 CFM’s

Air Changes Per Hour

How many air cleaners are needed to substantially remove
cigarette smoke from a 28’ x 40’ office with a 14’ ceiling?
  • 28’ x 40’ x 14’ = 15,680 cubic feet
  • Determine volume of air to be circulated each hour (e.g 10 air changes per hour would substantially reduce the smoke)
    • 15,680 c/f x 10 air changes/hr
    • 156,800 c.f./hour
    • 156,800 c.f./hour/60min/hr = 2613 c.f./minute
  • Determine # of air cleaners needed. (Desired Circulation – Air Cleaner Capacity)
    • 2,613 CFM – 1,000 CFM = 2.6 (2 or 3 units)

Sizing by Occupants

A restaurant occupies an average of 50 people.

(use the ASHRAE recommended minimum of 35 CFM per person.)

50 people x 35 CFM per person = 1,750 CFM

1,750 CFM/1,000 CFM = 1.75 (1 or 2 units)

The above information is provided for ESTIMATING PURPOSES only. Individual requirements vary based on part of the country, plant ventilation needs, etc…If a more accurate figure is required, please consult the services of a qualified engineer.

Exterior Buildings

Due to the fact that climactic conditions vary so much upon regions and location of the building, it is very difficult to estimate the ideal btu’s needed for each application. Certain conditions, however, will assist in your calculations:

  1. Very sunny area with maximum glass for visibility – 1 ton per 150 s/f
  2. Heavily shaded area – reduce capacity 10%
  3. Active traffic through door or constantly opening a sliding window – 1 ton per 75-100 s/f