How to Calculate the Efficiency of a Water Tube Boiler

Calculating the efficiency of any appliance is sensible if you want to get a handle on the energy footprint of your home or industry. A more efficient water boiler can save hundreds of dollars each year, and it can pay for itself in just a few years. Water tube boilers, where the water is circulated through a series of tubes heated directly, can be very efficient and produce super-heated steam. They are therefore suitable for certain industrial processes.

Things You'll Need

• Calculator
• Water tube boiler

Instructions

1. Calculating efficiency is as easy as following the equation:

   Efficiency % = output/input

   There will always be heat lost in any process, as described by the second law of thermodynamics. However, some heat conversion processes can be quite efficient. The average water boiler has an efficiency of 68 percent and can be as high as 95 percent on the super-efficient side.

2. Find the number of British Thermal Units (BTUs) that the boiler takes in and how much it gives out. This is usually listed on the outside of the boiler or furnace.

3. Divide the output by the input to gain a percentage. For example, a 190,000 BTU intake, and a 172,000 BTU output make for a 90.5 percent efficient boiler.

4. Use the heat loss method. Calculating efficiency by heat loss is a more accurate method of calculating efficiency; however, it requires greater knowledge of the combustion of the fuel heating the boiler. Typically industry standards require efficiency information (in one form or another) to be included in any device, especially if it is to be sold to the home.

Tips & Warnings

• 1 KWh = 3412.142 BTUs Because efficiency is expressed as a percentage, the units don't matter as long as they are the same.

References

• ASHRAE Boiler System Efficiency article
• Boiler types