How to Determine the Supply Power for Heat Blankets

Upon choosing a heat blanket for an application, it is important to understand the supply power requirements to avoid circuit failures or electrical damage. To figure this out, the (a) wattage of a heat blanket, (b) voltage of a heat blanket, and (c) maximum amperage capacity of the supply power (outlet) is needed for this calculation.

Calculating Watts

HEATCON heat blankets are available in many sizes and power options. However, whether its dimensions are 6”x6” or 24”x24”, heat blankets for composite repair are typically constructed with a watt density of 5 watts per square inch (5W/in²). This watt density allows the heat blanket to reach a 350°F cure temperature on most parts using typical ramp rates. Using the heat blanket dimension above, the watts for each size are as follows:

  • Heat Blanket A:     6” x 6”   (36in²)   x 5W/in² = 180W
  • Heat Blanket B:   24” x 24” (576in²) x 5W/in² = 2,880W

Standard Voltage

Outlet receptacles with voltage of 110/120V or 220/240V are commonly found in a multitude of locations to operate regular electrical machinery. To conform to this standard, our standard heat blankets are built to operate on either 120 or 220 volts.

Special Situations

Other voltage input power configurations are available for special circumstances and custom blanket requests. In addition, the electrical current, or amperage (A), available in some facilities may be limited to for some circuit breakers provides a maximum of 15A or 20A of current for a given set of outlets. In these cases, the watt density may have to be altered from the standard 5W/in² to accommodate the required blanket size and application. Consultation with HEATCON application engineers can guide you through this decision to achieve a workable solution.

Supply Power Calculation

Before you begin calculating supply power, it’s recommended to know what voltage is provided at your facility so you can make an educated decision for the right heat blanket. The Ohm’s Law formula is used to calculate supply power requirements.

W = A

For the examples above, both heat blankets will be constructed with 120V. In using the Ohm’s Law calculation, Heat Blanket A with dimension of 6”x6” / 120V has the following:

180W= 1.5A

In this calculation we can conclude that Heat Blanket A is supported by a 15A receptacle outlet. This supply power is common with smaller composite repairs.

In using the Ohm’s Law calculation, Heat Blanket B with dimension of 24”x24” / 120V has the following:

2,880W = 24A

In this calculation we can conclude that Heat Blanket B is not supported by a 15A receptacle outlet even though it is built with 120V. As a result, higher supply power is necessary to work in safe and effective conditions.

Technicians usually encounter this type of situation when repairs are larger therefore a larger heat blanket is needed. What is often overlooked is the supply power required to operate the heat blanket. Under this circumstance a receptacle and circuit that generates provides a higher electrical current is necessary. If a facility is not equipped with this type of supply power, an electrician should evaluate the conditions to determine if a higher capacity circuit and voltage outlet can be installed.

To learn more about our heat blanket options or how to choose the right heat blanket. Contact us at 206-575-1333 or email us at


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