Bosch Tronic 6100 C 27
#10 in ElectricFull review
For a two bathroom home in a warm climate that wants a compact whole home heater with a 2 year parts warranty, double what Rheem gives.
Amazon $636.60$636.60
The Bosch Tronic 6100 C 27 is the better tankless water heater overall, rated 3.1 to 2.9. The Bosch Tronic 6100 C 27 leads on heating power. The EcoSmart ECOS 18 wins on efficiency. The EcoSmart ECOS 18 costs $187.60 less ($449 vs $636.60).
EcoSmart ECOS 18
#14 in ElectricFull review
For a small home or apartment in a warm climate that wants whole house hot water on two breakers. Amazon stock was low when checked.
Amazon $449$449
Prices were last checked October 31, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the Bosch Tronic 6100 C 27 for heating power (27 kW vs 18 kW).
- Choose the EcoSmart ECOS 18 for efficiency (0.96 UEF vs 0.93 UEF).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every electric tankless water heater; a clear win is highlighted. How we rank explains each one.
| Factor weight | Bosch Tronic 6100 C 27 | EcoSmart ECOS 18 |
|---|---|---|
| Overall rating | 3.1/5 | 2.9/5 |
| Value 35% | 49 $23.58 per kW ($636.60, 27 kW) | 45 $24.94 per kW ($449, 18 kW) |
| Heating power 25% | 64 27 kW | 28 18 kW |
| Efficiency 15% | 38 0.93 UEF | 75 0.96 UEF |
| Warranty 25% | 29 5-year heat exchanger warranty | 29 5-year heat exchanger warranty |
Specifications
| Bosch Tronic 6100 C 27 | EcoSmart ECOS 18 | |
|---|---|---|
| Heating | ||
| Fuel | Electric | Electric |
| Electric power | 27 kW | 18 kW |
| Max flow | 5.3 GPM | 4.4 GPM |
| UEF | 0.93 | 0.96 |
| Installation | ||
| Voltage | 240 V | 240 V |
| Breakers | 120 A total | 80 A total |
| Weight | 14.8 lb | 9.3 lb |
| Features | ||
| Built-in recirculation | No | No |
| Wi-Fi | No | No |
| Heat exchanger warranty | 5 years | 5 years |
| Parts warranty | 2 years | 1 year |
| Released | 2023-01 | - |