Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
Stepping from the KBR 28-3A to the KBR 35-3A raises the input ceiling from 100,000 to 131,900 BTU/hr and output at 104/86 °F from 93,800 to 122,800 BTU/hr in the same 150 lb FS cabinet — while the minimum fire rises from 24,600 to 36,000 BTU/hr and the vent class shortens to the 35/42 limits.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Bosch Greenstar KBR 28-3A | Bosch Greenstar KBR 35-3A |
|---|---|---|
| Input rate, minimum | 24.6 MBH | 36 MBH |
| Input rate, maximum | 100 MBH | 131.9 MBH |
| Output rate, maximum (104/86 °F) | 93.8 MBH | 122.8 MBH |
| Weight (without packaging) | 150 lb | 150 lb |
| Sound pressure level | ≤ 33 dB(A) | ≤ 33 dB(A) |
| Maximum supply temperature | 190 °F | 190 °F |
| Maximum permissible operating pressure (PMS), heating | 30 psi | 30 psi |
Both are 150 lb heating-only floor boilers in the same 557 x 1048 x 555 mm cabinet with 33 dB(A) sound, 190 °F maximum supply and 30 psi pressure ratings. The KBR 35-3A adds roughly 32 MBH of input ceiling and 29 MBH of output over the 28-3A.
The modulation trade-off is real: minimum fire rises from 24,600 to 36,000 BTU/hr, so a home whose load sits far below 100 MBH would run the 35-3A at its low-fire floor more often. The FS venting tables also move the 35-3A into the 35/42 class with shorter maximum runs than the 21/28 class.
Physically nothing else changes — the cabinet, weight, sound and supply ratings are identical — so the decision is load size versus low-fire behaviour and the vent route's fit within the 35/42-class tables.
Bosch Thermotechnology
The Greenstar KBR 28-3A is a floor-standing heating-only Greenstar boiler: 24.6 to 100 MBH natural-gas input in the 557 x 1048 x 555 mm FS cabinet, rated 150 lb without packaging.
Bosch Thermotechnology
The Greenstar KBR 35-3A is a floor-standing heating-only Greenstar boiler: 36 to 131.9 MBH natural-gas input in the 557 x 1048 x 555 mm FS cabinet, rated 150 lb without packaging.
No. Its minimum fire is 36,000 BTU/hr against the 28-3A's 24,600 BTU/hr, so in a low-load home the smaller boiler tracks mild weather more closely.
No — the 35-3A sits in the 35/42 vent class (25 ft of 2" concentric with two elbows) while the 28-3A is in the 21/28 class (52 ft), per the FS manual tables.
No. All KBR floor models weigh 150 lb (68 kg) without packaging.
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 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.