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Model#: BWHN660EFONG

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Bosch 660EFONG Therm 660 EFO Natural Gas Therm Outdoor Tankless Water Heater

  • Bosch 660EFONG Therm 660 EFO Natural Gas Therm Outdoor Tankless Water Heater
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Product Overview

Additional Information


The Therm 660 EFO Tankless Water heaters is Bosch's most compact outdoor model, and comes loaded with features you've come to expect such as freeze protection and built-in high temperature compatibility of up to 160 Degrees F.
Eligible for up to $300 tax credit!
  • Outdoor installation with freeze protection
  • 83% thermal efficiency
  • 14,0000 maximum BTU input
  • 6.6 gallons per minute capacity at 35 Degree F rise
  • Minimum activation flow rate of 0.5 gallons per minute
  • Electronic ignition
  • Can be used in re-circulation and space heating applications
  • Therm 660 EFO Natural Gas Therm Outdoor Tankless Water Heater - 660EFONG


Width: 14 in.
Height: 20.5 in.
Depth: 7 in.
Energy Factor: 0.82
Flow Rate At 45 Degree F Rise: 5.3 GPM
Flow Rate At 55 Degree F Rise: 4.2 GPM
Gas Connection: 3/4 in. Male NPT
Gas Type: Natural Gas
Ignition: Electronic (120V plugs in)
Minimum Flow To Activate: 0.5 GPM
Power Input - Natural Gas: 20,000 - 140,000 BTU
Shipping Weight: 43.5 lbs.
Thermal Efficiency: 83%
Water Connection: 3/4 in. Male NPT



5.0 / 5.0
1 Review
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4 Stars
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1 Star
Would you recommend?
Yes (1)
Yes, I would recommend this to a friend
Great product and customer service!
We just switched from a tank water heater to the tankless Bosch Therm 660 EFO Natural Gas Therm Outdoor Tankless Water Heater. We have a bath and a half and so far so good. Many people are not familiar with Bosch, but they have been making these on-demand units for decades! My parents used them while my father was stationed in Germany in the 60s. The water heats up quickly and does not run out. I am anxious to get our next utility bill to see the savings there. Meanwhile, we will be putting the extra outdoor storage space to good use now that the old water heater tank is gone!
May 9, 2013

Questions & Answers

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Browse 7 questions Browse 7 questions and 8 answers
* on Jul 11, 2013
BEST ANSWER: From the Bosch Service manual that doesnt appear to be so, there is a conversion kit for it - though I have no idea how much - I live in HI and am looking at this also - but would need it on LP gas also.
will this work with propane LP gas?
Jeano on Sep 20, 2013
BEST ANSWER: No, this is designed to be used with natural gas only.
I just ordered (and received) the tankless heater 660EFO but it is informed that its remote control is an optional unit.
It seems that the unit can't even turn on without this remote control.
In your page, I can't see how to find one: BRC01US
Can you help?
Thanks for your time.
LeakFinder on Aug 31, 2013
BEST ANSWER: Unfortunately, we do not stock the remote in our warehouse. You can contact Bosch Tankless Water Heaters at 1-800-798-8169.
Can the bosch outdoor natural gas water heater be installed in a attached garage
Joe on Aug 30, 2013
BEST ANSWER: No, this water heater is designed to be installed outdoors only.
Peter on Aug 17, 2013
BEST ANSWER: Warranty information can be found in the manual on pages 50 and 51. Here is a link to the manual.
my friends in the country have one that runs on propane. unfortunately it has stopped working and there is no bosch service there. what techniques could they use themselves to try to get it working again?
fieldinski on Aug 4, 2013
BEST ANSWER: You can contact Bosch Tankless Water Heater directly at 1-800-798-8169.
Can this unit be mounted inside?
Susan on Jul 11, 2013
BEST ANSWER: No, this heater is for outdoor use only.


AquaStar Warranty 12 Year Warranty

This warranty applies to both new and factory-reconditioned AquaStar water heaters.


AquaStar water heaters warranted by Bosch will furnish a replacement heat exchanger and will furnish a replacement of any other part which fails in normal use and service within the applicable periods specified below, in accordance with the terms of this warranty. The Bosch Water Heating replacement will be warranted for the unexpired portion of the original warranty. This warranty will be valid only for water heaters in possession of the original purchaser as recorded on the warranty card.

The Heat Exchanger

If the heat exchanger fails within twelve (12) years after the original installation and operation, Bosch thermotechnology corporation will furnish a replacement heat exchanger. However, if the water heater is in an approved domestic hot water recirculation application, this heat exchanger warranty is limited to five (5) years from date of original installation and operation. If the water heater is installed in other than a single family dwelling, this heat exchanger warranty is limited to two (2) years from date of original installation and operation.

All Other Parts

If any other part fails within two (2) years after original installation and operation, Bosch Water Heating will furnish a replacement part free of charge.

Shipping Costs

In addition to supplying the replacement part(s), Bosch Water Heating will provide ground service delivery for these parts.Expedited or upgraded shipping will be charged to the customer.

This warranty does not cover any labor costs associated with service, removal or re-installation of part(s). All such costs must be borne by the Purchaser.


This warranty will not apply:

  1. to defects or malfunctions resulting from failure to properly install, operate or maintain the unit in accordance with the printed instructions provided;
  2. to damage or abuse, accident, neglect or freezing and other acts of nature;
  3. to damage resulting from operation with either the thermocouple or overheat sensor removed;
  4. to failure of the heat exchanger resulting from the operation of the water heater in a corrosive atmosphere or at water temperatures exceeding the maximum rating, or if the water heater is not supplied with potable water.
  5. to defects or damage cause by any attachment or modification, including any energy-saving device.

Note: The water heater must be free of damaging scale deposits, highly mineralized / unsoftened water and not subject to gas pressures greater than those shown on the rating plate, which must not be altered, defaced or removed.


It has come to our attention that products from Bosch Water Heating are being sold through on-line auctions and other unauthorized distribution channels. We believe that in some cases there are legitimate consumers trying to sell product that they have purchased through legitimate distribution channels. However, we are finding that some of the merchandise has actually been stolen from our customers. Please be advised that our product warranty is void with respect to stolen goods. Further, we reserve the right to require a legitimate sales receipt showing that the product was purchased from one of our customers in order to provide warranty coverage.

How to Make a Claim

  1. The Owner should contact the dealer who sold the water heater covered by this warranty or
  2. Owner should submit the warranty claim directly to Bosch Water Heating at the address listed below, and they will arrange for the handling of the claim.
  3. Whenever any inquiry or service request is made, be sure to include the water heater model number, the date of manufacture, date of installation, Dealer's name and the watts and voltage.
  4. When returning the water heater or component part(s), they must be individually tagged and identified with the Returned Goods Authorization # issued by Bosch Water Heating and shipped prepaid to Bosch Water Heating at the address below.


No one is authorized to make any other warranties on behalf of Bosch Water Heating. It is expressly understood that the replacement warranty of Bosch Water Heating shall be in lieu of any and all other warranties, express or implied, including warranties of merchantability or fitness for a particular use or purpose, and further that Bosch Water Heating shall not be liable for any loss or damage directly or indirectly arising from the use of the hot water heater, or for any consequential damages arising from such use (including damages from water leakage). Bosch Water Heating's sole liability with respect to any defect shall be for the replacement of defective part(s). Some states do not allow such limitations and exclusions, so the above may not apply to you. This warranty gives specific legal rights. You may also have other rights which vary from state to state. In the event that warranty service is required, reasonable proof of the effective date of installation and operation must be provided; otherwise it may not be possible to honor warranty. Bosch Tankless Water Heaters are only approved for installation/warranty in the US/Canada. Installing outside of US/Canada will void the Bosch Tankless warranty.