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Comparison
Verdict in brief
The A. O. Smith Burkay HW-399 and A. O. Smith Burkay HW-420 are both non-condensing boilers in the A. O. Smith Conservationist Burkay (hot-water boilers) line. The A. O. Smith Burkay HW-399 is rated 399,000 BTU/h natural and propane input and 319,200 BTU/h output, and the A. O. Smith Burkay HW-420 is rated 420,000 BTU/h natural and propane input and 336,000 BTU/h output. A. O. Smith Burkay HW-420 lists 21,000 more input than A. O. Smith Burkay HW-399 (420,000 against 399,000). Both list the same published shipping weight of 301 lb.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | A. O. Smith Burkay HW-399 | A. O. Smith Burkay HW-420 |
|---|---|---|
| Input rating | 399,000 BTU/h natural and propane | 420,000 BTU/h natural and propane |
| Output rating | 319,200 BTU/h | 336,000 BTU/h |
| Approximate shipping weight | 301 lb | 301 lb |
| Water inlet / outlet | 1-1/2" NPT inlet / 1-1/2" NPT outlet | 1-1/2" NPT inlet / 1-1/2" NPT outlet |
| Gas inlet | 3/4" NPT | 1" NPT |
| Fuel | Natural gas or propane (LP) | Natural gas or propane (LP) |
| Draft diverter outlet diameter | 10 in | 10 in |
| Recovery capacity (as printed) | 1,935 GPH at 20 °F rise (natural gas) | 2,036 GPH at 20 °F rise (natural gas) |
| Working pressure | 160 psi, ASME tested and certified | 160 psi, ASME tested and certified |
Published ratings: the A. O. Smith Burkay HW-399 is rated 399,000 BTU/h natural and propane input and 319,200 BTU/h output; the A. O. Smith Burkay HW-420 is rated 420,000 BTU/h natural and propane input and 336,000 BTU/h output. A. O. Smith Burkay HW-420 lists 21,000 more input than A. O. Smith Burkay HW-399 (420,000 against 399,000).
The gas connection differs: the A. O. Smith Burkay HW-399 lists 3/4" NPT, while the A. O. Smith Burkay HW-420 lists 1" NPT. The recovery capacity differs: the A. O. Smith Burkay HW-399 lists 1,935 GPH at 20 °F rise (natural gas), while the A. O. Smith Burkay HW-420 lists 2,036 GPH at 20 °F rise (natural gas).
Both records print the same shipping weight (301 lb), water connections (1-1/2" NPT inlet / 1-1/2" NPT outlet), fuel (Natural gas or propane (LP)) and draft diverter outlet diameter (10 in), per the cited sources.
A. O. Smith
The A. O. Smith Burkay HW-399 is a commercial gas-fired copper hot water boiler rated 399,000 BTU/h input and 319,200 BTU/h output, with 1-1/2" NPT water connections and a 3/4" NPT gas connection.
A. O. Smith
The A. O. Smith Burkay HW-420 is a commercial gas-fired copper hot water boiler rated 420,000 BTU/h input and 336,000 BTU/h output, with 1-1/2" NPT water connections and a 1" NPT gas connection.
The A. O. Smith Burkay HW-420 lists 420,000 BTU/h natural and propane, against 399,000 BTU/h natural and propane on the A. O. Smith Burkay HW-399, per the cited documentation.
The A. O. Smith Burkay HW-420 lists 336,000 BTU/h, against 319,200 BTU/h on the A. O. Smith Burkay HW-399.
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Sources and verification
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.