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Side-Arm Heat Exchanger for Water Heater, Stainless Steel, Select Model
Model / Configuration
25 in — 3/4 in DHW × 1 in system
$209
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Product details
Choose a stainless-steel Side-Arm Heat Exchanger for your boiler-fed domestic hot water system. These water-to-water units transfer heat from a boiler or hydronic loop to a storage water heater while keeping the two water circuits separate. Their fin-enhanced tube design supports heat transfer, and natural thermosiphon circulation can move water without a dedicated circulator pump in compatible installations.
Select from five models with listed capacities from 13,500 to 23,000 BTU/hr. Options vary by length, recommended tank size, wall construction on designated models, and plumbing connections. Compare the selected variation specifications before ordering. This side arm heat exchanger water heater range is intended for compatible systems using a boiler, outdoor wood furnace, or solar hot-water source.
Choose a model
- FES-70: 25 inches, 13,500 BTU/hr, recommended for 27-gallon tanks.
- FES-95: 33 inches, 19,000 BTU/hr, recommended for 40-gallon tanks.
- FES-115: 38-inch single-wall model, 23,000 BTU/hr, recommended for 60-gallon tanks.
- FES115DW: 38-inch double-wall model, 18,500 BTU/hr, recommended for 40-gallon tanks.
- FES-115-3/4: 38 inches, 23,000 BTU/hr, with 3/4-inch DHW and system connections.
Use the variation selector to choose the side arm hot water heat exchanger that matches your tank size and plumbing. Confirm all connection sizes and system requirements before installation.
Installation overview
For side arm heat exchanger installation, the unit is typically mounted vertically beside the storage tank to support natural thermosiphon circulation. Connection sizes vary by model. Follow the selected model manufacturer instructions and applicable plumbing codes, and use a qualified installer where required.
| Specification | FES-70 — 25 in | FES-95 — 33.1 in | FES-115 — 38.4 in |
|---|---|---|---|
| Model | FES-70 | FES-95 | FES-115 |
| Length | 25 in | 33.1 in | 38.4 in |
| Capacity | 13500 BTU/hr | 19000 BTU/hr | 23000 BTU/hr |
| Recommended tank size | 27 gal | 40 gal | 60 gal |
| DHW connection | 3/4 in NPT | 3/4 in FPT | 3/4 in FPT |
| System connection | 1 in NPT | 1 in FPT | 1 in FPT |
| Dimensions | 25 × 2 in | 33.1 × 2 in | 38.4 × 2 in |
| Heat-transfer area | 2.35 sq ft | 3.16 sq ft | 3.62 sq ft |
| Center-to-center distance | 20.28 in | 28.3 in | 33.7 in |
| Listed heat recovery | 3.2 hours | 3.4 hours | 3.8 hours |
| Weight | 4.1 lb | 5.8 lb | 6.3 lb |
| Warranty | 1.5 years against manufacturer's defectsPer source product page | 1.5 years against manufacturer's defectsPer source product page | 1 year against manufacturer's defectsPer source product page |
| Wall construction | — | — | Single wall |
| Specification | FES-95 — 33.1 in | FES-115 — 38.4 in | FES115DW — 38.4 in |
|---|---|---|---|
| Model | FES-95 | FES-115 | FES115DW |
| Length | 33.1 in | 38.4 in | 38.4 in |
| Capacity | 19000 BTU/hr | 23000 BTU/hr | 18500 BTU/hr |
| Recommended tank size | 40 gal | 60 gal | 40 gal |
| DHW connection | 3/4 in FPT | 3/4 in FPT | 3/4 in FPT |
| System connection | 1 in FPT | 1 in FPT | 1 in FPT |
| Dimensions | 33.1 × 2 in | 38.4 × 2 in | 38.4 × 2 in |
| Heat-transfer area | 3.16 sq ft | 3.62 sq ft | 3.62 sq ft |
| Center-to-center distance | 28.3 in | 33.7 in | 33.7 in |
| Listed heat recovery | 3.4 hours | 3.8 hours | 3.8 hours |
| Weight | 5.8 lb | 6.3 lb | 7.3 lb |
| Warranty | 1.5 years against manufacturer's defectsPer source product page | 1 year against manufacturer's defectsPer source product page | 1.5 years against manufacturer's defectsPer source product page |
| Wall construction | — | Single wall | Double wall |
| Specification | FES-115 — 38.4 in | FES115DW — 38.4 in | FES-115-3/4 — 38.4 in |
|---|---|---|---|
| Model | FES-115 | FES115DW | FES-115-3/4 |
| Length | 38.4 in | 38.4 in | 38.4 in |
| Capacity | 23000 BTU/hr | 18500 BTU/hr | 23000 BTU/hr |
| Recommended tank size | 60 gal | 40 gal | 60 gal |
| DHW connection | 3/4 in FPT | 3/4 in FPT | 3/4 in FPT |
| System connection | 1 in FPT | 1 in FPT | 3/4 in FPT |
| Dimensions | 38.4 × 2 in | 38.4 × 2 in | 38.4 × 2 in |
| Heat-transfer area | 3.62 sq ft | 3.62 sq ft | 3.62 sq ft |
| Center-to-center distance | 33.7 in | 33.7 in | 33.7 in |
| Listed heat recovery | 3.8 hours | 3.8 hours | 3.8 hours |
| Weight | 6.3 lb | 7.3 lb | 6.3 lb |
| Warranty | 1 year against manufacturer's defectsPer source product page | 1.5 years against manufacturer's defectsPer source product page | 1.5 years against manufacturer's defectsPer source product page |
| Wall construction | Single wall | Double wall | — |
| Specification | FES115DW — 38.4 in | FES-115-3/4 — 38.4 in |
|---|---|---|
| Model | FES115DW | FES-115-3/4 |
| Length | 38.4 in | 38.4 in |
| Capacity | 18500 BTU/hr | 23000 BTU/hr |
| Recommended tank size | 40 gal | 60 gal |
| DHW connection | 3/4 in FPT | 3/4 in FPT |
| System connection | 1 in FPT | 3/4 in FPT |
| Dimensions | 38.4 × 2 in | 38.4 × 2 in |
| Heat-transfer area | 3.62 sq ft | 3.62 sq ft |
| Center-to-center distance | 33.7 in | 33.7 in |
| Listed heat recovery | 3.8 hours | 3.8 hours |
| Weight | 7.3 lb | 6.3 lb |
| Warranty | 1.5 years against manufacturer's defectsPer source product page | 1.5 years against manufacturer's defectsPer source product page |
| Wall construction | Double wall | — |
| Specification | FES-115-3/4 — 38.4 in |
|---|---|
| Model | FES-115-3/4 |
| Length | 38.4 in |
| Capacity | 23000 BTU/hr |
| Recommended tank size | 60 gal |
| DHW connection | 3/4 in FPT |
| System connection | 3/4 in FPT |
| Dimensions | 38.4 × 2 in |
| Heat-transfer area | 3.62 sq ft |
| Center-to-center distance | 33.7 in |
| Listed heat recovery | 3.8 hours |
| Weight | 6.3 lb |
| Warranty | 1.5 years against manufacturer's defectsPer source product page |
| Wall construction | — |
Applies to all models
| Product type | Water-to-water side-arm heat exchanger |
|---|---|
| Material | 304 stainless steel |
| Design pressure | 150 psi |
| Test pressure | 225 psi |
| Operating temperature range | 18°F to 406°FAs listed on product pages |
| Certification | UL listedAs listed on product pages |
FES-70 — 25 in
- Model
- FES-70
- Length
- 25 in
- Capacity
- 13500 BTU/hr
- Recommended tank size
- 27 gal
- DHW connection
- 3/4 in NPT
- System connection
- 1 in NPT
- Dimensions
- 25 × 2 in
- Heat-transfer area
- 2.35 sq ft
- Center-to-center distance
- 20.28 in
- Listed heat recovery
- 3.2 hours
- Weight
- 4.1 lb
- Warranty
- 1.5 years against manufacturer's defectsPer source product page
- Wall construction
- —
FES-95 — 33.1 in
- Model
- FES-95
- Length
- 33.1 in
- Capacity
- 19000 BTU/hr
- Recommended tank size
- 40 gal
- DHW connection
- 3/4 in FPT
- System connection
- 1 in FPT
- Dimensions
- 33.1 × 2 in
- Heat-transfer area
- 3.16 sq ft
- Center-to-center distance
- 28.3 in
- Listed heat recovery
- 3.4 hours
- Weight
- 5.8 lb
- Warranty
- 1.5 years against manufacturer's defectsPer source product page
- Wall construction
- —
FES-115 — 38.4 in
- Model
- FES-115
- Length
- 38.4 in
- Capacity
- 23000 BTU/hr
- Recommended tank size
- 60 gal
- DHW connection
- 3/4 in FPT
- System connection
- 1 in FPT
- Dimensions
- 38.4 × 2 in
- Heat-transfer area
- 3.62 sq ft
- Center-to-center distance
- 33.7 in
- Listed heat recovery
- 3.8 hours
- Weight
- 6.3 lb
- Warranty
- 1 year against manufacturer's defectsPer source product page
- Wall construction
- Single wall
FES115DW — 38.4 in
- Model
- FES115DW
- Length
- 38.4 in
- Capacity
- 18500 BTU/hr
- Recommended tank size
- 40 gal
- DHW connection
- 3/4 in FPT
- System connection
- 1 in FPT
- Dimensions
- 38.4 × 2 in
- Heat-transfer area
- 3.62 sq ft
- Center-to-center distance
- 33.7 in
- Listed heat recovery
- 3.8 hours
- Weight
- 7.3 lb
- Warranty
- 1.5 years against manufacturer's defectsPer source product page
- Wall construction
- Double wall
FES-115-3/4 — 38.4 in
- Model
- FES-115-3/4
- Length
- 38.4 in
- Capacity
- 23000 BTU/hr
- Recommended tank size
- 60 gal
- DHW connection
- 3/4 in FPT
- System connection
- 3/4 in FPT
- Dimensions
- 38.4 × 2 in
- Heat-transfer area
- 3.62 sq ft
- Center-to-center distance
- 33.7 in
- Listed heat recovery
- 3.8 hours
- Weight
- 6.3 lb
- Warranty
- 1.5 years against manufacturer's defectsPer source product page
- Wall construction
- —
Applies to all models
- Product type
- Water-to-water side-arm heat exchanger
- Material
- 304 stainless steel
- Design pressure
- 150 psi
- Test pressure
- 225 psi
- Operating temperature range
- 18°F to 406°FAs listed on product pages
- Certification
- UL listedAs listed on product pages
Answers
Frequently asked questions
What does a side-arm heat exchanger do?
It transfers heat from a boiler or hydronic loop to domestic hot water in a storage tank while keeping the two water circuits separate.
How do I choose a model?
Choose by tank size, heating capacity, wall construction needs, and DHW and system connection sizes. Compare the selected variation specifications and confirm compatibility with your system.
How to install a side arm heat exchanger?
The unit is typically mounted vertically beside the storage tank to support natural thermosiphon circulation. Connection sizes vary by model. Follow the manufacturer instructions and local plumbing codes, and use a qualified installer where required.
Does it mix boiler water with domestic hot water?
No. Heat transfers between separate water circuits without mixing the fluids.
Installation help and contact
Any questions?Reach out to us.
Our team can help with product questions, sizing guidance, and next steps.