Electric Duct Heating Blog: Toast

Cost Effective Design of an Electric Duct Heater

Posted by Bill Brown on Wed, Feb 24, 2010 @ 09:11 AM

When specifying an electric duct heater an HVAC professional can help you save $$ and aggravation by designing the heater correctly the first time. The design engineer will need answers to a number of questions.

Information about the siteStandard Duct Heater

  1. Does the application allow open coil electric heat? Most HVAC installations do.
  2. What will the heat load be under the worst case conditions?
  3. Is "quiet operation" required? (ie: A classroom or doctor's office)
  4. Is the power to operate the heater available in the area where the conditioning is needed?
  5. What type of power is available? (both phase and voltage)

Duct system

To determine the appropriate kilowatts for the heater, the design engineer will need to know the duct size, the CFM and the temperature rise needed for the air exiting the duct. You may also want to consult with the engineer regarding staging. He can recommend the optimum number of stages, to help minimize surging of the building's power, for minimum cost.

How to save $$

Consulting with a HVAC design engineer regarding the number of kilowatts required for the job can often result in cost savings. For examlpe, a 20 KW heater at 240 Volts and 3 Phase can cost up to twice as much as a 19.6 KW heater with the same  phase and voltage. This is simply because the 20 KW load is over 48 amps and UL requires circuit fusing for any load over 48 amps.  You will save $$ if a 19.6 KW heater is adequate to do the job!

Other Considerations

  1. What is the control voltage and will it be supplied by the heater or another source?
  2. Will an Air Pressure Switch or a Fan Interlock be required?  (to prevent operation of the heater in the event of low or no air flow)
  3. To ensure the safety of service personnel, the duct heater control box can be configured with a door interlocking disconnect switch. This saves on installation cost since a separate service disconnect may not be required in the area.
  4. Duct heaters are available with many options including: fan motor interlock relays, additional fan motor fusing, plenums, square to round construction, single point line connections, quiet SCR or mercury contactors and step controllers to name a few.

Make sure to consult with an HVAC professional before making any decisions about your heating requirements.

Duct Heater Selection & Sizing

Tags: cost, effective, of, duct, heaters, design, electric