The Greenstar combi line is Bosch's residential combi boiler product — the only major German-engineered combi available in the US. Single wall-mounted unit provides both space heating (radiators, baseboards, in-floor radiant) and domestic hot water.
Greenstar lineup
| Model | BTU | DHW GPM | Typical home |
|---|---|---|---|
| Greenstar 100 | 96k | 3.7 | 1-2 bath, small home |
| Greenstar 131 | 131k | 5.0 | 2 bath, mid-size |
| Greenstar 151 | 151k | 5.8 | 2-3 bath flagship |
Outdoor variant (Greenstar 100-OD) for warm-climate exterior wall-mount.
When Greenstar wins over Navien NCB
- Cold-climate hydronic homes (New England, Mountain West)
- Homes already running Bosch HVAC (ecosystem fit)
- European-style hydronic design preferred
- Long-term ownership where the conservative German engineering pays back
When Navien NCB is better
- Volume US combi market (Navien is the segment leader)
- Wider US installer network
- Higher capacity options (NCB-240, NCB-300 exceed Greenstar 151)
- Buffer-tank cold-sandwich elimination on Navien NPE-A2 tankless equivalent
Hydronic install requirements
Same as any combi — primary/secondary loop, expansion tank, air separator, outdoor reset. Use a Bosch-experienced hydronic installer.
Warranty
10 years heat exchanger / 5 years parts / 1 year labor.
Bottom line
Greenstar is the right call for cold-climate hydronic homes with a Bosch-experienced installer, or for buyers who prefer European engineering. For most US combi installs, Navien NCB dominates by market share — but Greenstar is a legitimate engineering alternative.