Is the water heater undersized for the application
-
There are many methods of sizing various applications, i.e. ASHRAE sizing tables, or ASPE domes-
tic water heating design manual, re-confirm the water demand required for the application.
-
Re-confirm the flow rates of the fixtures. Was the tank sized for shower heads at 2.0 gpm, when the
actual heads are 5.0 gpm? Use a bucket and a stopwatch to determine fixture flow rates.
-
Evaluate the hot water usage pattern for a day. Is the peak demand unusually high for the application?
-
Has the demand for domestic hot water changed since the system was installed? A bathroom remod-
eling project with a newly installed whirlpool tub will drastically change the domestic water demand.
Is the boiler system properly sized
-
Is the boiler providing the required output of BTU’s to meet the domestic water load?
Temp Rise ºF = Desired Temp.ºF - Incoming Temp.ºF
8.33 = Density of Water lbs/gal. x 1 Btu/lbs ºF
Example:
A single family home with a 3.0 gpm shower fixture and a 150,000 Btu/hr output boil-
er capacity. Is the boiler capacity adequate to deliver 115ºF water for an extended period?
The boiler capacity is capable of delivering 4.6 gpm continuously which is adequate for this appli-
cation.
Action Item:
- Measure the BTU input to the boiler by clocking the gas meter or finding the oil flow rate
based on nozzle size and pump pressure.
-
Does the hot water system need to be wired for domestic priority? For systems in which either the
storage or BTU’s available are marginal it is recommended to wire the domestic water heater in a pri-
ority manner.
-
Is the boiler piping to the water heater properly sized to allow the required flow rate for maximum
BTU transfer? The temperature differential of the boiler supply and return water should be 20ºF to
30ºF.
Insufficient Hot Water
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Summary of Contents for HL-20
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