Bosch Thermotechnology · Greenstar Wall (ZBR/ZWB)
Bosch Greenstar ZBR 35-3A
The Greenstar ZBR 35-3A is the 132 MBH-class wall-hung heating-only Greenstar: 36,000 to 131,900 BTU/hr natural-gas input in the standard 103.6 lb wall cabinet, with the shorter vent runs Bosch allows for the 35/42 size class.
Key figures
- Max input
- 131.9 MBH
- Max CSA output
- 122.8 MBH
- AFUE
- —
- Min input
- 36 MBH
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Bosch Greenstar ZBR 35-3A in practice
The ZBR 35-3A is the first wall model whose minimum fire steps up — 36,000 BTU/hr minimum against 131,900 BTU/hr maximum natural-gas input — so in a low-load home the smaller 28-3A tracks mild weather more closely. It keeps the family's 103.6 lb, 440 x 850 x 353 mm cabinet and stays heating-only, with sound rated at 44 dB(A) against 39 dB(A) on the 21/28 class.
Its vent group is shared with the 42-class models: the manual limits the 35/42 class to 25 ft of straight 2" concentric pipe with two elbows (NG), or 44 ft of 3"/5" concentric pipe with one elbow, so longer runs must use 3" or the concentric system. Max supply temperature is 187 °F and heating pressure is rated 30 psi.
The ZBR 35-3A uses the same Heatronic control and two-character fault-code table as the other -3A wall models. Bosch's CA pages market the Greenstar family at 95% AFUE; the I&O manual prints input/output tables and altitude derates to 7,000 ft instead of an AFUE figure.
Best suited to
- Detached homes whose heat-loss calculation exceeds the 100 MBH input ceiling of the 28-3A
- Replacements where the 103.6 lb wall cabinet and 440 x 850 x 353 mm footprint must be kept
- Systems whose vent route fits the 35/42-class lengths in the manual tables
Applicability and support
- Model number
- ZBR 35-3A
- Canadian availability
- available
- Production status
- current
- ROMA supplies
- Confirmed at consultation
- ROMA services
- Confirmed at consultation
- Warranty
- Not verified
Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Specifications
Published specifications
Values as published by Bosch Thermotechnology. Units are shown with every value; notes flag conflicting sources or missing figures.
| Specification | Value | Note |
|---|---|---|
| Input | ||
| Input rate, minimum | 36 MBH | 36,000 BTU/hr at 180/79 °F (82/26 °C), natural gas. |
| Input rate, maximum | 131.9 MBH | 131,900 BTU/hr at 180/79 °F (82/26 °C), natural gas; altitude tables in the manual reduce the maximum above 2,000 ft. |
| Output | ||
| Output rate, maximum (104/86 °F) | 122.8 MBH | 122,800 BTU/hr at 104/86 °F water temperatures per the manual technical table. |
| Venting and air | ||
| Venting | 2" NG only; 3" or 3"/5" (80/125 mm) concentric for LPG | Per the manual: the 35/42 model class is limited to 25 ft of straight 2" concentric pipe with 2 elbows (NG), or 44 ft of 3"/5" concentric pipe with 1 elbow. Termination type changes the tables. |
| Physical and connections | ||
| Weight (without packaging) | 103.6 lb | 103.6 lb (47 kg) without packaging per the manual. |
| Dimensions (W x H x D) | 17-21/64" × 33-15/32" × 13-57/64" (440 × 850 × 353 mm) | Per the manual technical data table. |
| Sound pressure level | ≤ 44 dB(A) | Per the manual technical data table. |
| Maximum supply temperature | 187 °F | 187 °F (86 °C). |
| Maximum permissible operating pressure (PMS), heating | 30 psi | 30 psi (2.07 bar). |
| Nominal water capacity (heating) | 0.925 gal | 0.925 gal (3.5 l). |
| Permissible inlet gas pressure | NG 3.5–10.5 in. W.C.; LPG 8–13 in. W.C. | NG is the factory default; LPG only after successful gas conversion with the included conversion kit. |
| Operating limits and other | ||
| Fuel | Natural gas or propane | Separate NG and LPG ratings in the manual; LPG requires the gas conversion kit included with the appliance. |
Frequently asked questions
Why does the 35-3A have a higher minimum fire than the 21/28 models?
The manual prints 36,000 BTU/hr minimum input for the 35-3A against 24,600 BTU/hr for the 21-3A and 28-3A, so the larger boiler's lowest firing step is higher.
Are the vent limits different on this size?
Yes. The 35/42 class allows 25 ft of straight 2" concentric pipe with two elbows versus 52 ft for the 21/28 class, and 44 ft of 3"/5" concentric with one elbow versus 50 ft.
Is the ZBR 35-3A a combi?
No. ZBR codes are heating-only; the wall-hung combis are the ZWB models, which Bosch Canada documents as the Greenstar Combi 100p/151p pair plus the ZWB 35-3A.
Questions about the Bosch Greenstar ZBR 35-3A?
Describe what the boiler is doing and get a straight answer about the next step.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Compare and explore
- Bosch Greenstar ZBR 28-3A vs ZBR 35-3AComparison
- Bosch Greenstar ZBR 35-3A vs ZBR 42-3AComparison
- Bosch Greenstar ZBR 35-3A vs ZWB 35-3AComparison
- Bosch Greenstar ZBR 21-3ASame series
- Bosch Greenstar ZBR 28-3ASame series
- Bosch Greenstar ZBR 42-3ASame series
- Bosch Greenstar ZWB 35-3ASame series
- Greenstar Wall (ZBR/ZWB) series hub
- Buying guide
Sources and verification
- Bosch Home Comfort Canada — Greenstar Boilers · accessed September 7, 2026
- Greenstar Wall Boilers Installation and Service Manual (6721853955) · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.