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iHeat AHS27-D AHS24-D AHS18-D Electric Tankless Water Heaters

Original price $379.95 - Original price $489.95
Original price
$379.95 - $489.95
Current price $379.95


iHeat logoThe iHeat AHS Series tankless water heaters save energy by turning on only when you need hot water. Flow sensors detect outgoing and incoming water temperature as well as the flow rate to automatically adjust the heating elements to precisely achieve the temperature you set. These temperature sensors don't touch the water, which means that they last much longer, and reqsrcuire less maintenance. Plus, AHS models have built-in safety features to protect you and your children from scalding from overheated water.

iHeat AHS water heaters are in the same class as the ECO18 through ECO27 shown in the Related Gadgets tab near the bottom of this page. Here are some advantages:

• The flow sensor is inside the inlet pipe, eliminating the risk of leaks from metal and plastic joints.
• The electronic control board is made with higher-quality surface mount design.
• Features a touch screen display instead of a clunky, imprecise knob.
• AHS heaters can be diagnosed through the USB port at the bottom of the unit. Refer to the last page of the manual.


• Unlimited hot water supply
• No venting needed
• Compact design means installation anywhere at home
• Save up to 60% on your water heating bill
• Easy installation
• .99 EF means it is much more efficient than tank heaters
• Stainless Steel construction
• Competitively priced compared to tank heaters without the waste
• Save valuable space

ETL certifiedFeatures

• Heat Exchangers are made of 100% stainless steel; resists corrosion
• Intelligent electronic controls increases energy safety and efficiency
• Able to install in series
• Self Modulating Feature
• Accurate output temperature circuits
• USB Diagnostics
• Digital temperature setting from 82°F to 140°F
• Optional high temperature setting for 170°F
• ETL certified to UL 499 standard


AHS27D / AHS24D / AHS21D AHS11D/ AHS14D / AHS16D / AHS18D
Dimensions American Heat AHS Series Electric Tankless Water Heaters American Heat AHS Series Electric Tankless Water Heaters
Weight 17.5 lbs. 13.7 lbs
Cover ASTM 304 Stainless Steel 1.5 mm
Body/heat exchanger ASTM 304 Stainless Steel
Element 3 Brass Flange/Copper 2 Brass Flange/Copper
Pipe fittings 3/4" NPT, stainless steel
Activation flow rate 0.25 gallons per minute
Operation pressure Min 25 PSI, Max 150 PSI
Warranty 1 year on heating elements, 3 years on components, 5 years on heat exchanger

Flow rate (GPM) at various temperature rise levels (in degrees Fahrenheit, °F)

Model ↓
Temp Rise→
GPM 1.2 1.3 1.4 1.5 1.7 1.9 2.1 2.5 3.0 3.8 5.0
AHS14D GPM 1.5 1.6 1.7 1.9 2.1 2.4 2.7 3.2 3.8 4.8 6.4
AHS16D GPM 1.7 1.8 2.0 2.2 2.4 2.7 3.1 3.6 4.4 5.4 7.3
AHS18D GPM 1.9 2.0 2.2 2.5 2.7 3.1 3.5 4.1 4.9 6.1 8.2
AHS21D GPM 2.2 2.5 2.7 3.0 3.3 3.8 4.3 5.0 6.0 7.5 10.0
AHS24D GPM 2.5 2.7 3.0 3.3 3.6 4.1 4.7 5.4 6.5 8.2 10.9
AHS27D GPM 2.8 3.2 3.5 3.8 4.2 4.8 5.5 6.4 7.6 9.6 12.7

Electrical Specifications by Model

Elements 3 3 3 2 2 2 2
Voltage 240 240 240 240 240 240 240
Max kW 27 24 21 18 16 14 11
Max Watts 27000 24000 21000 18000 16000 14000 11000
Each Supply 9kW 8kW 7kW 9kW 8kW 7kW 5.5kW
Max AMPS 112 100 87.5 75 67 58 46
HZ 50/60 50/60 50/60 50/60 50/60 50/60 50/60

Install the following breakers in the main electrical panel based on the model being installed:

Breakers for main electrical panel without the sub-Panel quantity 3 DP 40 Amp breakers quantity 3 DP 40 Amp breakers quantity 3 DP 40 Amp breakers quantity 2 DP 40 Amp breakers quantity 2 DP 40 Amp breakers quantity 2 DP 40 Amp breakers quantity 2 DP 30 Amp breakers


User Manual
Product Warranty
Product Specifications

Frequently Asked Question ("FAQ")

Q1: Can the units in the AHS series run on 208V or 220V?
A1: Yes, they will operate on 208V, 220V or 240V. However, the performance will be "derated", meaning the heater will have a proportional loss in heating capacity as the voltage drops.

Q2: Is a maximum output temperature of 170°F possible with control board upgrade?
A2: Yes as of 12-26-2019, this option is available. Choose the high-temperature option in the menu above.
* NOTE: 170°F is the maximum not the guaranteed output temperature! The output temperature depends on flow rate and incoming water temperature. See GPM vs. temperature rise table.

Q3: Can I use this like a boiler, for radiant floor heating, baseboard heating, hydronic or closed-loop applications?
A3: Most radiant floor/baseboard, or hydronic or boiler, heating applications call for water heating greater than 140°F. Most of these hot water heating systems operate best at about 160 degrees F. Older, oil-fired boilers have a setpoint of 200°F. The factory-set maximum temperature for the AHS series heaters is 140°F. You can order the heater with a maximum (not guaranteed) output temperature of up to 170°F, according to its heating capability. Just choose that option in the menu next to the price. In a closed-loop system, the AHS27D will achieve this in a short time for residential applications.

Most other hot water heating systems provide either 1 GPM or 4 GPM. With the AHS27D, according to our temp rise (delta-T) chart above, you will get a temperature rise of 184 degrees F at 1 GPM. Most other hot water systems operate with a delta-T of about 17°F or less. So, for the 170°F output setting, the AHS27D must have have water inflow of 153°F. But the AHS27D can provide 2.5x to 10x the minimum needed flow rate of 4 GPM. Therefore, the AHS27D is a perfect solution for boiler and radiant floor heat. Plus, it is small, smart and silent. If you're considering this unit for hot water baseboard or hydronic service, and you have a 200 amp electrical panel, the AHS27D is a good choice.

A general, simplified design is as follows. Each zone returns or feeds into a header which then feeds the pump. The pump feeds into the heater's cold water inlet connection. From the heater's hot water ouput, water flows into a header which then splits into your individual zones. Put the water on/off valves on the return side. Add a standard expansion tank to hold the system at 15 PSI. The cold water inlet is through a one-way RV-type water valve.