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Flash T-K1

How tankless water heaters work


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Tankless Water Heater
How The Flash Operates
Storage Tank vs. The Flash, T-K1
Gas Piping
Water Connections
Recommended Sizing for Hot Water Line
The Flash Water Heater Operation Flow Chart

Dimensions   16.5"x24.5"x8.3"


Tankless water heaters also known as on-demand, or instantaneous have been around for decades, but have had limited market penetration in the United States. In other parts of the World where energy costs are higher and space is limited, these tankless water heaters are the standard. Tankless water heaters use a different heating system than the storage tanks type water heaters found in most homes today. Tankless water heaters are more efficient and can generate a continuous supply of hot water. Because of the flow through, on-demand system, your hot water faucet or appliance becomes the trigger that will activate this type of water heater. FLASH

The Flash water heater, model T-K1, is an on-demand, tankless gas water heater. This space saving, highly energy efficient water heater can deliver over 200 gallons of hot water per hour and since there is no tank to run out, you get an ENDLESS supply of hot water.

The Flash utilizes the latest in technological controls for efficient water heating. These include computer modulated gas valves, electronic temperature sensor, electronic water flow sensor, electronic ignition (no pilot burner), computerized safety devices and even pipe heaters to protect the unit when the temperature is near freezing. Because of these advance controls the Flash is compact, about the size of a small Pullman suitcase, yet 5 times more powerful than the average storage tank water heater. The Flash has a self modulating input rating of 37,000 to 165,000 Btu.

The Flash with its durable design and rust resistant powdered coating is made to be installed outdoors also.

[Top] How the Flash Operates

The T-K1 only bums gas when you need hot water.

1) Open a hot water faucet.

2) When the flow rate exceed 0.75 GPM the computer electronically ignites the powerful stainless steel burner.

3) Then the computer measures water temperature, flow rate, and adjusts the gas valves so you maintain the 140*F outlet hot water temperature.

  1. Close the hot water faucet and the computer turns off the gas and burners.



  Flash Water Heater  Model No. T-K1  Storage Tank Water Heater  (50 gallon AGA approved) 
Size 2.2 cubic feet  7.5 cubic feet
Dimensions 24.5" x 16.5" x 8.3"  60" x 20"diameter 
Weight (filled with water)  65 lbs.  415 lbs. 
First Hour Rating (DOE)  216 GPH 70 gallons (40.5GPH) 
Energy Factor 0.81 0.54 
Thermal Efficiency  NG Max. 82.3%, LPG 84.7% 76% 
Standby Heat Loss  0% 20% 
Vent 4" Diameter Outdoor Powered Flue  Draft hood
Freeze Prevention Devices  Yes No 
Computer Modulated Gas Valves  Yes No 
Self Monitoring Computerized Safety Devices  Yes No 
Pilot Burner No Yes 
Electronic Flow Sensor  Yes No 
Powered Combustion  Yes No 

[Top] With a storage tank, you store 40-75 gallons of hot 140*F water 24 hours a day, 7 days a week though you only use hot water a couple times a day. The tank type heaters constantly lose heat through the flue and tank walls trying to maintain 140*F. The heater cycles on and off to maintain this temperature. This causes cracking of the exterior walls and sediment build up which will eventually cause your storage tank to leak. The storage tank is designed to wear out and be replaced in time. Also, the storage tank water heaters only have a limited amount of hot water and after that is gone you have to wait for the tank to get heated again.

The Flash heats the water only when there is a demand for hot water. Opening a hot water faucet, ignites the powerful burners and the computer monitors the water temperature and adjusts the burners according to the need. High demand, high heat. Low demand, low heat. With no tank to run out you get an endless supply of hot water. No tank to heat means no standby heat loss. The Flash provides a continuous flow of hot water and will never run out, but the flow rate is limited to the temperature that you set. With a self modulating input rating of 37,000 to 165,000 Btu's this unit can handle a small application like a bathroom faucet and can take care of large demand application like a washing machine or dishwasher. This heater is designed to give you the maximum amount of hot water. With the 140*F temperature setting, you will need to mix it with cold water to get the water temperature you desire.

Household Flow Rates

Appliance/ Use  Flow Rate (gallons per minute) 
Lavatory Faucet  0.4 - 1.0 GPM 
Bath Tub  2 GPM
Shower 1.6 GPM
Kitchen Sink  1 - 1.4 GPM 
Dishwasher  2 GPM 
Washing Machine  2 GPM 

Flow Rates of T-K1

Temperature Rise (*F)  Gallons Per Minute (GPM) 
90*F 2.9 GPM 
80*F 3.3 GPM 
70*F 3.8 GPM 
60*F 4.4 GPM 

Base on hot water outlet temperature 140 F


The Flash is more efficient than normal storage tank type water heaters and save energy. However the Flash requires more Btu's to heat water instantly. This means the Flash burns a lot of gas for shorter periods and only when you require hot water. Normal storage tanks burn at a gradual rate because it has plenty of time through the day to keep your 30-75 gallons of hot water stored and it will cycle on and off to maintain this temperature.

To get the most out of your Flash water heater, make sure you size the gas piping accordingly. The Flash will work more efficiently when it has an adequate supply of gas. Follow the National Fuel Gas Code or your local building codes to size the gas pipe

The Flash comes with an automatic adjusting pressure regulator which has been set at the factory and should not be adjusted. The computer modulates the gas valves so you can maximize the use of your Flash. This unit is designed for one type of gas only. Make sure you have the right type for your installation.

Gas Line

Nominal Iron Pipe Sizes  1/2"  3/4"  1" 
T-K1 Natural Gas 


Not Recommended  25'  80' 

Data from the National Fuel Gas Code.


All water connections are 3/4". Make sure you correctly attach the hot and cold lines. If you reverse connections on this heater, it may cause a dangerous situation. Use approved connectors when installing so replacement and maintenance can be done with ease. Allow adequate space on the piping side for maintenance.


Do not install this water heater under an overhang less than 3 feet from it's top. The area under the overhang must be open on 3 sides in case of outdoor intallation.
Minimum Clearances from Noncombustible Construction for indoor installation
Top of heater  12 inches 
Back of heater  1 inch
Front of heater  4 inches 
Side of heater  2 inches
Piping side  6 inches
For Installation Only on Noncombustible Floors


  1. Follow all local codes and ordinances or in the absence of local codes, follow the National Fuel Gas Code or in Canada the Installation Codes for Gas Burning Appliances.
  1. Adhere to the minimum clearances specified in the manual. This unit is equipped with a powered flue, therefore do not have the vent assembly pointing toward a window or an opening in a building.
  1. The gas connection is 3/4" and the water connections are 3/4". Remember to leak test all the gas and water piping before operation. A temperature and pressure relief valve is required on the hot outlet.
  1. The minimum flow rate to ignite the burners is 0.75 GPM. The flow governor is installed so the water temperature can reach 140*F. The maximum outlet flow rate is 5.3 GPM.
  1. For easy installation, install gas and water shutoff valves and use couplings or flex connectors to connect to the gas and water lines.
  1. There is a flow governor restricting flow to 5.3 GPM. This is to maximize the hot water available to the user.

[Top] Recommended Sizing for Hot Water Line


Plumbing Fixture Description Fixture Units
Combination Bath/ Shower  4
Whirlpool Bath  4
Shower 2
Lavatory  1
Clothes Washer  4
Dishwasher  1.5
Kitchen Sink  1.5
Pressure Range 30 to 45 PSI  Fixture Units Recommended
Pipe Size Length to the End of Hot Water Line 
  100' 200' 300' 400'
3/4" 3-12 1-6 1-5 0-4
1" 12-25 6-17 5-13 4-12
1-1/4" 25-48 17-32 13-25 12-21
Pressure Range 46 to 60 PSI  Fixture Units Recommended
Pipe Size Length to the End of Hot Water Line 
  100' 200' 300' 400'
3/4" 5-17 3-11 2-8 1-6
1" 17-36 11-25 8-20 6-18
1-1/4" 36-78 25-52 20-39 18-33
Pressure Range 60+ PSI  Fixture Units Recommended
Pipe Size Length to the End of Hot Water Line 
  100' 200' 300' 400'
3/4" 6-20 4-13 3-10 2-8
1" 20-39 13-32 10-26 8-22
1-1/4" 39-78 32-74 26-54 22-43

For best results, refer to the Uniform Plumbing Code. This is only a guide and does not take precedence over your local building and plumbing codes.
  [Top] The Flash Water Heater Operation Flow Chart

Stand By Mode

1. Electricity On

2. Power Indicator Light On

3. persists Check OK

4. No Flame Sensed

To Turn On

(Average time from step 1 to 7 is approximately 3 seconds)

1. Hot Water Tap Opened

2. Water Flow Sensor On

(>0.75 gallon/min.)

3. Fan Motor On

Fan Motor > 1,000 RPM

4. Ignitor On

5. High Limit Fuse OK

6. Source Gas Solenoid Valve On (SVm)

Gas Solenoid Valve On (SV1)

Proportioning Valve On (VGO)

Burners Lit

7. Flame Rod detects flame

8. Fire Lamp Lit

9. Ignitor Off

10. Thermistor Senses Temperature

11. Computer Monitors All Safety Functions

and monitors fan speed, flow sensor, thermistor,

proportioning valve to heat the water correctly.

To Turn Off

(Average time from step 1 to 5 less than 3 seconds.)

1. Hot Water Tap Closed

2. Water Flow Sensor Off

3. Source Gas Solenoid Valve Off (SVm)

Gas Solenoid Valve Off (SVI)

Gas Solenoid Valve Off (5V2)

Proportioning Valve Off (VGo)

4. Flame Rod detects no flame

5. Fire Lamp Off

6. Fan Motor Off

T-K1 Engineering Data

Recovery Rating (DOE) : 203 Gallons per Hour

Energy Factor Natural Gas : 0.70

Propane Gas : 0.72

Thermal Efficiency 80 %

Combustion Fan Assisted

Vent 4" round w/ vent cap for outdoor use

Electrical input 120VAC, 60 Hz

Dimensions 16.5"x24.5"x8.3"

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Flash Tankless Water Heater or a Storage Tank?

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Electric Water Heaters, Tankless Electric Water Heaters

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