Name: Optimal opti 18kW 240V 3.7GPM 25-Year Warranty Electric Tankless Water Heater
Brand: Optimal
SKU: 5015212527
Price: 597 USD
Availability: InStock
Rating: 4.8 (91 reviews)

Here are some similar items...

Optimalopti plus 15kW 240V 3 GPM Wifi Enabled 25-Year Warranty Electric Tankless Water Heater

Optimalopti 27kW 240V 4.5GPM 25-Year Warranty Electric Tankless Water Heater

Optimalopti 15kW 240V 3 GPM 25-Year Warranty Electric Tankless Water Heater

Optimalopti plus 18kW 240V 3.7GPM Wifi Enabled 25-Year Warranty Electric Tankless Water Heater

Optimalopti 12kW 208V 2.5GPM 25-Year Warranty Electric Tankless Water Heater

WestinghouseApolo Performance 18 kW 4.2 GPM 240-Volt Smart WiFi Control Tankless Electric Water Heater

Stiebel EltronTempra 36 Plus 240-Volt 36-kW-kW 7.03-GPM Tankless Electric Water Heater

A.O. SmithSignature Series 240-Volt 14-KW 2.7-GPM Tankless Electric Water Heater

392

A.O. SmithSignature 900 50-Gallon Tall 10-year Warranty 240-volt Smart Hybrid Grid Capable Heat Pump Water Heater with Leak Detection

110

A.O. SmithSignature 100 50-Gallons Tall 6-year Warranty 4500-Watt Double Element Electric Water Heater

5954

A.O. SmithSignature Series 240-Volt 18-KW 3.5-GPM Tankless Electric Water Heater

389

A.O. SmithSignature 100 30-Gallon Short 6-year Warranty 4500-Watt Double Element Electric Water Heater

3060

A.O. SmithSignature 100 50-Gallons Short 6-year Warranty 4500-Watt Double Element Electric Water Heater

5895

A.O. SmithSignature Series 240-Volt 22-KW 4.3-GPM Tankless Electric Water Heater

468

A.O. SmithSignature 100 40-Gallons Short 6-year Warranty 4500-Watt Double Element Electric Water Heater

7235

Best Price. Guaranteed

Find a lower price on an exact item? We'll match it. Some exclusions apply.

Price Guarantee

FREE Returns

Return it in store or ship it back for free. Eligibility rules apply.

Return Policy

Pay Your Way

Credit card, PayPal or Buy Now, Pay Later options available at checkout. Your choice.

Payment Options

The opti18 electric tankless water heater can replace a tank heater for the whole home, act as a point of use, or supplement a hybrid as a booster to extend hot water availability. Refer to the sizing map in the images to learn more about the model that is best for you. With its powerful 18kW heating system and one-of-a-kind ultrasonic design, this water heater is engineered for energy efficiency and space savings. Expert, in-house, customer support stands behind the industry leading 25-year warranty for reliability you deserve in a product meant to last. Set it and forget it to the exact temperature you desire for endless hot water with an accuracy of 1°.

Save up to 50% on your water heating costs
Save space and reclaim an entire closet worth of storage
25-year residential warranty covers all components including heat exchanger
Patented US design is the only water heater with ultrasonic flow technology
In-house, expert support is here to answer all your water heating questions
Advanced, built in diagnostics make troubleshooting easy
Dry-fire protection prevents elements from burning out
Straightforward installation with standard 3/4 inch water connections and no venting needed
Built in LED diagnostics let you monitor system status at a glance

General
Color/Finish Family	White	Use Location	Indoor
Type	Tankless	Display Type	Digital
Power Source	Electric	Installation Type	Wall mount
Grade	Commercial/Residential

Dimensions
Depth (Inches)	3.5	Water Connection Size	3/4-in
Family Size	4	Weight (lbs.)	12
Height (Inches)	16.9	Width (Inches)	11.4

Features
Annual Fuel Utilization Efficiency % (Percentage)	0	Point of Use	No
Grid Capable	No	Scale Prevention	No
High Efficiency	Yes	Super High Efficiency	Yes
Hub Required	No	Uniform Energy Factor	0.99
Leak Detection	Yes	Voice Controlled	No
Maximum Gallons per Minute	3.7	Voltage (Volts)	240
Maximum Temperature (Fahrenheit)	140	Water Connection Location	Bottom
Minimum Temperature (Fahrenheit)	72	Water Heater Style	Short
Overheat Shut-Off	Yes	Wattage (Watts)	18000

Compatibility
App Compatibility	No	Works with Apple HomeKit	No
Bluetooth Compatibility	No	Works with iOS	No
Smart Compatible	No	Works with SmartThings	No
Wi-Fi Compatibility	No	Works with the Google Assistant	No
Works with Amazon Alexa	No	For Use with Mobile Homes	No
Works with Android	No	For Use with RVs	No

Warranty
Warranty	25-year limited

Certifications
CA Residents: Prop 65 Warning(s)	No	Safety Listing	ETL safety listing
ENERGY STAR Certified	No	AHRI Certified	No

Miscellaneous
UNSPSC	40101800

Check out the Best Selling Water Heaters on Lowes.com

Review

4.8 out of 5

91 Reviews

2 Star

97% Recommend this product

Ratings may include incentivized customer reviews.

+ 16

What Customers Are Saying

Customers overwhelmingly praise the tankless water heater for delivering endless hot water, enabling multiple appliances to run simultaneously without depletion. Reviewers highlight instant heating efficiency, compact design, and a 25-year warranty as standout features. Support staff receive consistent recognition for responsiveness and expertise. Most find installation straightforward with clear instructions, though professional electrical work is required. A few note a minor learning curve with water flow control and occasional sizing considerations, but nearly all customers consider the investment worthwhile and highly recommend the product.

Customer review summary generated by AI, including incentivized reviews.

91 Customer Reviews

Sort By

Works great. Easy temperature adjustment.

Would Recommend

Just installed 2 weeks ago. Easy installation and water hook up.

Rwb63September 26, 2026
Verified Purchaser

Was this Review Helpful ?

Quick Service

Would Recommend

I installed under my kitchen Island counter, and I wasn't getting any hot water, called support and they helped me through some tests (using my voltmeter). narrowed it down to a circuit board and it was shipped next day. It was pretty easy to replace, and I've been very impressed with it so far. Will update after I put it to use for a while.

LarrySeptember 13, 2026
Verified Pro

Was this Review Helpful ?

Great product for a great price.

Would Recommend

I purchased this for a guest house and was very pleased with the ease of installation and very impressed with the warranty. It provides a great amount of hot water on demand without any wasted energy. A great value for the price.

Michael MSeptember 7, 2026
From opti 15kW 240V 3 GPM 25-Year Warranty Electric Tankless Water Heater Verified Purchaser

https://photos-us.bazaarvoice.com/photo/2/cGhvdG86bG93ZXM/1d3b74ed-ca43-5a9e-ac14-6db28c3ca3c7

https://photos-us.bazaarvoice.com/photo/2/cGhvdG86bG93ZXM/15593632-eb79-56b9-8a27-991882a37441

Was this Review Helpful ?

Works great!

Would Recommend

We had to replace the control board, it was damaged in transit. It had worked great since the fix.

Ash RJune 30, 2026
From opti 27kW 240V 4.5GPM 25-Year Warranty Electric Tankless Water Heater Verified PurchaserIncentivized

Was this Review Helpful ?

People should know that shopping at Lowe’s is nice

Would Recommend

In the store, I was attended to politely.

NachoJune 12, 2026
From opti 27kW 240V 4.5GPM 25-Year Warranty Electric Tankless Water Heater Verified Purchaser

Was this Review Helpful ?

Excellent upgrade!!

Would Recommend

Easy to install and the instant hot water. The instructions were clear and complete. The 25 year warranty is a huge plus for this product.

BmanJune 9, 2026
From opti 27kW 240V 4.5GPM 25-Year Warranty Electric Tankless Water Heater Verified PurchaserIncentivized

Was this Review Helpful ?

Page 1 Page 2 Page 3 Page 10

20 Questions

Read All Q&A

Sort By

Optimal: Featured Videos

COMPARE PRODUCTS

		Name	Current Item Optimalopti 18kW 240V 3.7GPM 25-Year Warranty Electric Tankless Water Heater
		Ratings	91
		Type	Tankless
		Height (Inches)	16.9
		Width (Inches)	11.4
A.O. SmithSignature 100 50-Gallons Tall 6-year Warranty 4500-Watt Double Element Electric Water Heater	A.O. SmithSignature Series 240-Volt 28-KW 5.5-GPM Tankless Electric Water Heater	Optimalopti plus 18kW 240V 3.7GPM Wifi Enabled 25-Year Warranty Electric Tankless Water Heater	Stiebel EltronTempra 36 Plus 240-Volt 36-kW-kW 7.03-GPM Tankless Electric Water Heater	Optimalopti plus 27kW 240V 4.5GPM Wifi Enabled 25-Year Warranty Electric Tankless Water Heater	A.O. SmithSignature Series 240-Volt 32-KW 6.2-GPM Tankless Electric Water Heater	Stiebel EltronTempra 24 Trend 240-Volt 24-kW-kW 4.68-GPM Tankless Electric Water Heater	A.O. SmithSignature 100 50-Gallons Tall 6-year Warranty 40000-BTU Natural Gas Water Heater	A.O. SmithSignature 100 40-Gallons Tall 6-year Warranty 35500-BTU Natural Gas Water Heater
5954	392	41	11	41	383	14	3355	3740
Tank	Tankless	Tankless	Tankless	Tankless	Tankless	Tankless	Tank	Tank
59	18.13	16.9	14.5	17.2	18.13	14.5	60.75	61.81
20.5	17	11.4	16.63	14.5	17	16.63	21	20