Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The Hi Delta SS HD401 adds 100 MBTUH of input and 84 MBTUH of output over the Hi Delta SS HD301 on the same Hi Delta SS platform. The HD401 is the top Hi Delta SS size: 399 MBTUH input and 335 MBTUH output, with the efficiency measure changing from 85% AFUE to 84% thermal efficiency and the flue stepping to 6 in.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Raypak Hi Delta SS HD301 | Raypak Hi Delta SS HD401 |
|---|---|---|
| Input | 299 MBH | 399 MBH |
| Output | 251 MBH | 335 MBH |
| Thermal efficiency | 85 % | 84 % |
| Flue outlet | 5 in | 6 in |
| Weight | 250 lb | 300 lb |
| Maximum water flow | 44 GPM | 44 GPM |
The HD301 is rated 299 MBTUH input and 251 MBTUH output with not printed turndown; the HD401 is rated 399 MBTUH input and 335 MBTUH output with not printed turndown. HD301 is rated 85% and HD401 84% in the same efficiency column, so the larger size does not give up rated efficiency.
The HD401 is the top Hi Delta SS size: 399 MBTUH input and 335 MBTUH output, with the efficiency measure changing from 85% AFUE to 84% thermal efficiency and the flue stepping to 6 in. Both share the same 44 gpm maximum water flow, so the step up does not enlarge the pump or piping envelope. Shipping or operating weight moves from 250 lb to 300 lb, which matters for rigging and floor loading.
Both sizes are documented in the same official Raypak submittal for the Hi Delta SS family, so the decision is a heat-loss and plant-layout question rather than a documentation difference: size to the calculated design-day load, then check flow, connection and venting dimensions against the submittal for the exact model.
Raypak
The Raypak Hi Delta SS HD301 is a compact non-condensing copper finned-tube commercial hydronic boiler rated 299 MBTUH input and 251 MBTUH output at 85% AFUE, with a 5 in flue and a 250 lb shipping weight per submittal 241922.
Raypak
The Raypak Hi Delta SS HD401 is a compact non-condensing copper finned-tube commercial hydronic boiler rated 399 MBTUH input and 335 MBTUH output at 84% thermal efficiency, with a 6 in flue and a 300 lb shipping weight per submittal 241922.
Submittal 241922 prints 85% AFUE for HD151-HD301 and 84% thermal efficiency for the HD401.
The HD401 at 399 MBTUH input and 335 MBTUH output, with outdoor R-model variants listed by Raypak.
A consultation includes a heat-loss review so the size is right the first time.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.