Raypak Digital 406A
Good value for in-ground pools outside low NOx areas, provided it comes from an authorized dealer so the warranty holds.
Amazon $4,421.17$4,421.17
3.5/5
A low NOx, salt tolerant in-ground pool heater for owners who buy online and can live with a short warranty.
- 399,900 BTU/hHeating input
- 84%Efficiency
- Natural gas or propaneGas type
- 1 yearWarranty
Check price at Amazon$5,099
Price checked October 31, 2026. As an Amazon Associate we earn from qualifying purchases.
Pros
- Cupro-nickel heat exchanger stands up better to salt systems and unbalanced water than plain copper
- Low NOx certified, so it can be installed in California and other strict air districts
- Wide 125 GPM flow range works with big variable speed pumps without a bypass
- Runs from a remote thermostat or pool automation over simple 2 or 3 wire terminals
Cons
- Only a 1 year parts warranty with no labor when bought online
- No built in Wi-Fi or app control
- Big input needs a large gas line and meter
The Hayward H-Series family
Every Hayward H-Series model we rank, smallest first. Ratings compare each against its own size.
| Model | Heating input | Rating | Price |
|---|---|---|---|
| Hayward H-Series H135FD | 135,000 BTU/h | 2.6/5 | $2,399 |
| Hayward H-Series H150FD | 150,000 BTU/h | 2.6/5 | $2,999 |
| Hayward H-Series H200FD | 199,900 BTU/h | 3.2/5 | $3,699 |
| Hayward H-Series H250FD | 250,000 BTU/h | 2.3/5 | $3,999 |
| Hayward H-Series H400FD (this one) | 399,900 BTU/h | 3.5/5 | $5,099 |
How it scores
The rating comes from 4 measured or published factors, each scored 0-100 against fixed reference points for its size. How we rank explains each one.
Specifications
| Model number | W3H400FDN / W3H400FDP |
|---|---|
| Heating | |
| Gas input | 399,900 BTU/h |
| Gas type | Natural gas or propane |
| Thermal efficiency | 84% |
| Condensing | No |
| Low NOx | Yes |
| Heat exchanger | Cupro-nickel |
| Max water flow | 125 GPM |
| Installation and controls | |
| Ignition | Electronic |
| Venting | Both |
| Digital controls | Yes |
| Automation or app | Yes |
| Weight | 195 lb |
| Warranty | 1 year |
Alternatives in this size
Sta-Rite Max-E-Therm 400
A Pentair built heater for owners on Pentair automation who want low NOx and high efficiency; compare prices with the MasterTemp first.
Amazon $4,499$4,499
Raypak Digital 336A
Good value for in-ground pools outside low NOx areas, provided it comes from an authorized dealer so the warranty holds.
Amazon $3,615$3,615
Compare
Compare the Hayward H-Series H400FD with any other gas pool heater →
More from Hayward: every Hayward product ranked.