Bosch install requirements vary substantially by product family. Greentherm tankless is similar to other tankless brands. Greenstar combi adds the hydronic complexity. Tronic POU mini-tank is the simplest (plug-in install). Tronic Heat 3000 electric tankless is the most demanding on electrical service.
Greentherm gas tankless
Gas line sizing
| Model | BTU | Min gas line (back to meter) |
|---|---|---|
| Greentherm 5300 | 120k | ½" up to 30 ft / ¾" over 30 ft |
| Greentherm 7.2 | 180k | ¾" required |
| Greentherm 9000 / 9900 / 9999 | 199k | ¾" required (1" over 50 ft) |
Venting
- Condensing models (9000, 9900, 9999): 2" or 3" Schedule 40 PVC. Up to 100 ft equivalent length
- Non-condensing (7.2): stainless Category III venting
- Outdoor variant (9000-OD): no venting; cabinet weather-sealed
Condensate drainage
Condensing models produce 1-2 gallons/day. Trap + drain or condensate pump required.
Water softener
Required above 11 grains per gallon hardness for warranty compliance.
Greenstar combi — hydronic specifics
Combi installs are significantly more complex than tankless. Required:
- Primary/secondary loop design — boiler primary loop circulates through a hydraulic separator or closely-spaced tees
- Expansion tank — sized for system volume + heating temperature range
- Air separator — Spirovent or equivalent
- Dirt separator — required by Bosch warranty
- Pressure relief valve — 30 psi typical, separate from internal valve
- Backflow preventer — on the fill loop
- Zone valves or circulators — for multi-zone homes
- Outdoor reset sensor — mandatory; modulates supply temp to outdoor conditions
Use a Bosch-experienced hydronic installer. Generic plumbers often miss the design requirements.
Tronic POU mini-tank — simplest install
Most Tronic 6000 C and 3000 T units are 120V plug-in. Install:
- Mount under sink with provided bracket
- Connect cold supply and hot supply with flex lines
- Install T&P discharge to drain or floor
- Plug into nearest 120V outlet
- Open isolation valves, bleed air via the hot tap
- Verify operation; expect 20-30 min to first hot water from a fully-cold unit
Tronic Heat 3000 electric tankless — electrical-critical install
| Model | Power | Min electrical service |
|---|---|---|
| US3 | 11.5 kW | 100A service, 48A circuit |
| US7 | 27 kW | 125A service, 112A circuit |
| US9 | 36 kW | 150A service, 150A circuit |
| US12 | 36 kW | 200A service, 150A circuit |
Electrical service sizing is the #1 install failure mode. Many older US homes can't support US9 or US12 without a service upgrade ($2,000-5,000 additional). Verify electrical service capacity BEFORE buying.
Permits
Permits required in most US jurisdictions for gas tankless, combi, and any work involving 240V electrical changes. Tronic POU mini-tanks may not require permits (varies by jurisdiction — verify locally).
Commissioning
- Purge air from gas line (gas units)
- Open inlet/outlet isolation valves
- For combi: fill hydronic loop, purge air, set pressure (12-15 psi cold)
- Power on; verify display
- Set temperature
- For condensing: verify condensate drain flowing
- Pair to Home Comfort app if applicable
- Register warranty
Bottom line
Greentherm and Tronic POU installs are within range of most competent plumbers. Greenstar combi requires Bosch-experienced hydronic installer. Tronic Heat electric tankless requires verifying electrical service capacity first — undersized service is the most common cause of buyer's regret.