NP138 – CERAMIC INSULATOR (HEAT KIT / DUCT HEATER, 3/8 IN)

Napco NP138 ceramic insulator for electric heat kits and duct heaters, 3/4 inch outside diameter with a 3/8 inch bore and a 7/16 inch width. These support the element wire where it passes through the frame, and they crack and drop out with age, which is what shorts a heat kit to the cabinet. Napco is now part of Supco.

Specs

• BrandNapco
• Part NumberNP138
• TypeCeramic insulator / bushing
• Outside Diameter3/4 in
• Inside Diameter3/8 in
• Width7/16 in
• MaterialCeramic
• ApplicationElectric heat kit and duct heater element support

How do I size a heat kit for my air handler?

Rule of thumb: ~100 CFM per kW of strips. So a 1,600 CFM air handler (4 tons cooling) handles up to about 15 kW. Going beyond your air handler's CFM capacity makes the strips overheat and trip the high-limit. Always verify against your air handler's spec sheet for max kW.

Can I add electric heat to my heat pump system?

Yes — heat pumps almost always use electric strips as backup ("auxiliary heat" or "emergency heat"). The thermostat energizes the strips when outdoor temps drop below balance point (typically 35-40°F in DFW). Match the heat kit to your air handler model.

What does the suffix on the part number mean?

The suffix typically indicates breaker configuration: - BRK = factory breaker included - BR = breakerless (you provide the disconnect) - Other suffixes = circuit count, voltage taps, or thermostat compatibility

How long does an electric heat kit last?

20+ years typical for the kit itself; individual heating elements (sheath heaters) may fail in 8-15 years from cycling. Most kits have replaceable elements — you don't have to replace the whole kit for one bad strip.

Why is my heat kit tripping the high-limit?

Restricted airflow is the #1 cause: clogged filter, dirty blower wheel, undersized return, closed-off supplies. The strips overheat when air doesn't move across them fast enough. Diagnose airflow before condemning the heat kit or limit switch.