Racor Spin-On Series diesel fuel filter/water separators are available with optional 200W resistance in-bowl heaters by special order at the time of purchase, or as retrofit kits such as this one.
Placing the heat source just below the filter allows for maximum heat transfer.
This RK 22354-01 Retrofit Heater is designed for use with Series 200 Spin-On Series Fuel/Water Separators: 215R, 230R, 245R.
The bowl in this kit is 4" in diameter and includes a water drain fitting.
In dual or triple manifold systems, heating elements are usually installed in each filter.