Fluid heater with perforated flame holder

A fluid heater, comprising:

• a tank having an inlet and an outlet;
• a flue extending through the tank and having first and second ends;
• a nozzle positioned and configured to emit a fuel stream into the flue;
• a flame holder having a plurality of apertures extending therethrough and configured to hold a flame substantially within the plurality of apertures, the flame holder being located inside the flue, positioned to receive the fuel stream and to hold the flame entirely within the flue;
• and
• a controller configured to control a flow of fuel to the nozzle according to a temperature of a fluid within the tank;
• wherein the controller is configured to transition from stopping the flow of fuel to admitting the flow of fuel when the temperature of the fluid drops below a first temperature threshold.

A fluid heater, comprising:

• a tank having an inlet and an outlet;
• a flue extending through the tank and having first and second ends;
• a nozzle positioned and configured to emit a fuel stream into the flue;
• and
• a flame holder having a plurality of apertures extending therethrough and configured to hold a flame substantially within the plurality of apertures, the flame holder being located inside the flue, positioned to receive the fuel stream and to hold the flame entirely within the flue;
• wherein the fluid heater further comprises a water heater comprising:
• a combustion tube having a length L, the combustion tube defining an air column on an inside of the tube and a water volume outside of the tube and inside the tank, the tube having an inlet end configured to receive combustion air and an outlet end configured to output combustion products;
• wherein the nozzle comprises a hydrocarbon gas nozzle configured to output a hydrocarbon gas stream into the air column inside of the tube;
• wherein the flame holder comprises a perforated flame holder disposed in the air column, the perforated flame holder having a body with a thickness t, the body defining an input side aligned to receive the hydrocarbon gas stream and the combustion air, an output side opposite the input side disposed to output the combustion products, and
• wherein the apertures comprise a plurality of perforations extending through the thickness t from the input side to the output side, the perforated flame holder being configured to hold a combustion reaction supported by the hydrocarbon gas and the combustion air within the plurality of perforations;
• and further comprising:
• a support structure configured to support the perforated flame holder between the inlet end and the outlet end of the combustion tube at a distance not equal to L/4 from the inlet end of the combustion tube.