MIZUDO FDG-CS120AW-LP 120,000 BTU Propane Tankless Water Heater

What it delivers

The MIZUDO FDG-CS120AW-LP 120,000 BTU Propane Tankless Water Heater is a propane tankless with a 120,000 BTU/h burner and a stated maximum flow of 5.1 GPM.

At a 45°F rise (mild inlet water to a 120°F set point) it holds about 4.1 GPM, 2 showers at 2 GPM; in winter, at a 70°F rise, about 2.6 GPM, 1 shower at 2 GPM. Check it against your own fixtures.

The line must deliver about 1.3 gallons of propane an hour when it fires flat out. The requirement calculator adds it up; a licensed fitter confirms the pipe.

Its exhaust runs hot, so the vent must be the material its manual lists, usually stainless; budget for the vent kit.

The listing describes its venting as: Outdoor Installation.

From the listing: connectivity: WiFi; material: 5.1 GPM, 120,000 BTU, Indoor and Outdoor; model: FDG-CS120AW-LP.

The listing gives dimensions of 14.56 in (W) x 22.83 in (H).

Right unit for this house?

Install it when

One shower at a time in cold climates
Propane homes
Replacing a gas tank heater

Look at another unit when

More than 1 winter shower at once
Homes without a gas line

Strengths and trade-offs

Strengths

120,000 BTU/h input
Up to 5.1 GPM

Trade-offs

Gas line may need upsizing
Stainless venting costs more
Annual flushing on hard water

Install limits

Figures are the maker's or seller's own. Flow at a rise is our estimate from the input; gas, venting and electrical work needs a licensed professional.

Rated performance

Every figure below comes from the source shown in brackets. Where the maker doesn't state something, we say so instead of estimating.

Model number	FDG-CS120AW-LP	Retailer
Dimensions (seller)	14.56"W x 22.83"H	Retailer
Voltage	120 V	Retailer
Max flow (maker)	5.1 GPM	Retailer
Input (maker)	120,000 btu_per_hour_per_foot_per_fahrenheit	Retailer
Material	5.1 GPM, 120,000 BTU, Indoor and Outdoor	Retailer
Fuel	propane	Retailer
Venting	Outdoor Installation	Retailer
Connectivity	WiFi	Retailer

Rival units at this flow

ThermoMate CZ480LP Propane Tankless Water Heater114,000 BTU/h, up to 5.3 GPM.

GASLAND CS422BLP 113,000 BTU Propane Tankless Water Heater113,000 BTU/h, up to 5.0 GPM.

ThermoMate CZ422LP Propane Tankless Water Heater113,000 BTU/h, up to 5.0 GPM.

More gas tankless water heaters rated for similar demand

Full gas tankless water heaters spec grid · Every MIZUDO unit in the catalog

Final verdict

A solid propane tankless for one shower at a time in cold climates.

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Questions buyers ask

How many showers can the MIZUDO FDG-CS120AW-LP 120,000 BTU Propane Tankless Water Heater run at once?

From its 120,000 BTU/h input we estimate about 4.1 GPM at a 45°F rise and 2.6 GPM at a 70°F rise, so 2 two-GPM showers with mild inlet water and 1 in a cold winter. The maker's flow chart for this model is the final word.

What size gas line does the MIZUDO FDG-CS120AW-LP 120,000 BTU Propane Tankless Water Heater need?

At full fire it uses about 116 cubic feet of natural gas an hour or 1.3 gallons of propane. The pipe size depends on the length of the run and every other gas appliance on it; the maker's manual and a licensed gas fitter decide it.