Bosch Therm 660 EFO Tankless Water Heater


The Energy Star Bosch Therm 660 EFO offers up to 6.6 GPM of hot water for outdoor installation. This is a mid-capacity model that is ideal for homes with 2-3 bedrooms. With heavy-duty construction and high maximum heat, it is also suitable for commercial settings.

This Bosch Therm 660 EFO water heater review is designed to help you evaluate this model for your own purposes. If you want to compare it to similar models head to head, see our long list of tankless water heater reviews from Bosch, Rinnai, Takagi, Noritz and other leading brands. Our goal is to allow you to do all the necessary research for your next water heater right here on this site.

The top features of the Bosch Therm 660 EFO water heater start with the 140,000 BTU maximum input burner. It can create enough hot water to deliver 4.2 to 6.6 GPM, depending on the temperature of the incoming water. In mild/warm climates, the capacity will be on the upper end of that range.

This is an ideal model for residential use where it will serve a 1-3 bedroom home – or 2 points of hot water use at once. With a temperature range of 100 degrees F to 160 degrees F, it can also be used in commercial settings where sanitization is a priority. The default setting is 122 F, but it can be quickly adjusted up or down and will stay within 2 degrees of the set temperature to reduce the risk of accidental burns. Both natural gas and liquid propane models are available.

If you’re interested in comparing this model with other high-temperature tankless heaters, a good place to begin is with the Takagi T-K Jr-NG water heater.

The Bosch Therm 660 EFO tankless water heater is built for outdoor installation. The non-freeze technology means that it can be used in any climate. The benefit of outdoor installation is that there is less venting required, so the costs will be less. While not Bosch’s most efficient model, the 83% thermal efficiency does meet Energy Star guidelines and will help control energy use and utility bills.

Bosch backs this model with a standard 15-year heat exchanger warranty, but just a 3-year warranty with direct recirculating applications. The warranty is also 15 years if the system uses a recirculating storage tank like the Ariston mini-tank. All other parts are covered by a 5-year warranty.

If you need very hot water – and a lot of it – the Bosch Therm 660 EFO tankless water heater offers it along with good efficiency and a durable build that should last 15-20 years.




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