Side Arm Heat Exchanger - 38" Double Wall Stainless Steel 3/4" & 1"NPT 18,500 Btu

AB Side Arm Heat Exchangers have a compact, lightweight design that allows for a quick and easy installation. It is made with stainless steel 304 and has 3/4" (DHW side) and 1" (System side) NPT. Designed with natural thermosiphon heating technology, this heat exchanger is enhanced with fins to allow for higher heat transfer efficiency and to help reduce cross contamination for potable water. This fin-enhanced design, which is 5-8 times bigger than the traditional bare tube design, produces both significant turbulence on the system side and faster heating at a greater capacity. This type of heat exchanger is recommended for smaller households of about 1-3 people or households with lower hot water usage. The advantage of the double wall model is that the added wall further prevents cross-contamination and protects against leaks, should one occur. The capacity of this particular model is 18,500 Btu. This product has a 1.5 year warranty against manufacturer's defects and is UL listed.

Product Information

FES-115DW Capacity
18,500 Btu Connection Size
(DHW / System)
3/4" / 1"
Water to
Heat Transfer
3.62ft2 C-C Distance
Works with
(Tank Size)

40gal Heat Recovery
  3.8 Hours Materials
304 Stainless Steel

150psi Test
225psi Dimensions
38.4" x 2"
Min. Operating
 18F Max. Operating
406F    Weight

FAQ and Support
Sizing Guide:

33" works with 40gal. water heaters.
38" works with 60gal. water heaters.
38" Double Wall works with 40gal. water heaters.

The difference between single wall and double wall models is that the second wall helps prevent contamination in the water if a leak should happen. These heat exchangers are recommended for households of 1-3 people or households that don't use as much hot water.
We have worked with heating systems for over 10 years and are happy to help you with any questions or concerns that you may have. You can email us at or call 833-328-6888 for help with your heating projects.