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Comparison
Verdict in brief
The Delta Limited H3-749B adds 100 MBTUH of input and 84 MBTUH of output over the Delta Limited H3-649B on the same Delta Limited platform. The 649B and 749B are the middle 2-stage sizes; the 749B adds 100 MBTUH of input and 84 MBTUH of output with the same 2 in water, 1-1/4 in gas and 8 in flue connections.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Raypak Delta Limited H3-649B | Raypak Delta Limited H3-749B |
|---|---|---|
| Input | 650 MBH | 750 MBH |
| Output | 546 MBH | 630 MBH |
| AHRI thermal efficiency | 84 % | 84 % |
| Firing stages | 2 firing stages | 2 firing stages |
| Water connection | 2" NPT | 2" NPT |
| Flue outlet | 8 in | 8 in |
| Weight | 590 lb | 675 lb |
The H3-649B is rated 650 MBTUH input and 546 MBTUH output with 2:1 turndown; the H3-749B is rated 750 MBTUH input and 630 MBTUH output with 2:1 turndown. Both models carry the same published efficiency figure, so capacity is the variable rather than efficiency.
The 649B and 749B are the middle 2-stage sizes; the 749B adds 100 MBTUH of input and 84 MBTUH of output with the same 2 in water, 1-1/4 in gas and 8 in flue connections. Both share the same 90 gpm maximum water flow, so the step up does not enlarge the pump or piping envelope. Shipping or operating weight moves from 590 lb to 675 lb, which matters for rigging and floor loading.
Both sizes are documented in the same official Raypak submittal for the Delta Limited 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.
The Raypak Delta Limited H3-649B is an indoor non-condensing copper-fin commercial hydronic boiler rated 650 MBTUH input and 546 MBTUH Type H output at 84% thermal efficiency, with 2-stage firing and a 8 in flue.
The Raypak Delta Limited H3-749B is an indoor non-condensing copper-fin commercial hydronic boiler rated 750 MBTUH input and 630 MBTUH Type H output at 84% thermal efficiency, with 2-stage firing and a 8 in flue.
546 MBTUH and 630 MBTUH Type H output respectively, at 84% thermal efficiency per the 242015 submittal.
Yes — both are 2-stage models, shown as 2:1 on the product page model rows.
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.