Is your Water Energy Inefficient or Damaging to Your Water Heater?

Water and energy connecting the dots:

Water relative to functions like Green Building, Sustainable Building, Energy Efficiency or Conservation is often targeted as a resource to conserve or use in a renewable way with solar heating in the residential markets.  But not enough is said about water quality in relationship to energy efficiency or performance.  Heating domestic hot water is estimated to be 13% of household energy consumption, making it the 2^nd highest energy consuming equipment in the home after heating and cooling equipment.(Source EPA )  However, if water is also being used to heat the home, then the boiler or water heating equipment would contribute to a larger portion of the household energy demand.

Water is a compound with unique and amazing attributes. For example, water has a phenomenal capacity to hold heat.  Its absolute freezing temperature is -460^oF.  Common sense may lead us to believe that once water freezes it would not retain any heat.  However, to understand the heat capacity of, we could take a pound of water and a pound of gold at the absolute freezing point and apply to each the same amount of heat.  Then gold would reach 2000^oF and be flowing. But the temperature of the pound of water would have only risen 160^o thus actually raising its temperature to only -300^oF.

Water is an excellent and economical means of conducting heat and has been used by residential and commercial mechanical contractors for a long time for heating and cooling buildings.   In areas where hard water minerals are prevalent the boilers are either operated on soft water or undergo de-scaling maintenance on a routine schedule in order to keep the systems in operation.   Water containing minerals when heated will precipitate and deposit these minerals in the pipes causing them to clog.

If you think about it, you understand that common sense is not a reliable method for assessing water‘s usability or purity. Clean water is such a part of our lives that it is easy to presume water is all the same. But water is never just water and it is not the same even among neighbors.   Water molecules act as a submicron mini-bus.  It has this ability to carry away whatever it touches, and water as a flowing liquid becomes the infrastructure for transporting soluble and insoluble compounds, including minerals found in the underground water supplies.  These invisible hard water minerals precipitate out of the water when heated and deposit in pipes and on heating elements proportional to their concentration in the water.

High mineral content in water is a problem:

Water containing calcium, magnesium and silicate minerals make-up what is referred to as hard water. These are some of the same minerals that get promoted as “good minerals” to have in our drinking water by various disciplines.  However minerals create operational problems for water heating equipment.   The warranties for an on-demand water heater or tank less hot water heater can be voided when the water hardness is above 3.5 grains per gallon.  Rheem refers to this void in their warranty this way:  “This Limited Warranty will not cover: ….malfunctions or failures caused by lime or mineral build-up.”   In other warranties I have seen the word “liming” used to refer to the mineral deposit or build-up.  

Hard water is mostly measured by grains per gallon (gpg) and is commonly expressed this way in water analysis reports. It is also expressed as parts per million (ppm) with one grain equal to 17.1 ppm.     The US Department of Interior quantifies hard water mineral content as follows:

Soft:                              Less than 1.0 gpg         less than 17.1 ppm               

Slightly Hard:              1 to 3.5 gpg                  17.1 to 60    ppm                           

Moderatly Hard:          3.5 to 7.0 gpg               60 to 120 ppm                               

Hard:                              7.0 to 10.5 gpg             120 to 180 ppm                           

Very Hard:                    10.5 and over               180 and over     

Justification for recognizing the problem:

The Battelle Memorial Institute conducted a study to test the effect of softened water and hard water as it relates to the energy efficiency of hot water heaters and appliances in the household. And it formulated a differential for estimating the carbon footprint assessment of homes using softened water vs. hardwater.

The study introduces controllable amounts of hard water and soft water to the following units:

• 10 gas water heaters, 40 gal, 38,000 BTU/h burners
• 10 Electric water Heaters, 40 gal, 45,000 W heating elements
• 10 Tank less Gas water heaters, 199,000 Btu/h burners

Five were tested with unsoftened well water containing 26 grains per gallon (gpg) of water hardness, primarily Calcium Carbonate and 0.99 ppm of Iron.  And 5 of each were operated using water pre-softened to remove hardness minerals below 0.55 gpg and 0.27 ppm of Iron.

The study was set up to provide performance results based on increments of 5 grains per gallon (gpg) of water hardness ranging from 0 gpg to 30 gpg.  Each week the thermal efficiencies were calculated by monitoring the following data:

• Water temperatures and flow.
• For gas heaters: the gas used, BTU content and variations in usage.
• For electrical heaters: the Watt-hour measured for electricity consumptions.

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What the Study found:

 In general the study found the electric and gas storage water heaters and the on-demand gas water heaters using softened water performed well throughout the entire testing period.  Each unit maintained the factory estimated efficiency through out the testing period and did not require any de-liming of heating elements or pipes through out the testing period.  As reported in the Battelle Memorial Institute Executive Summary quite the reverse is true for the electric and gas storage water heaters and on-demand gas water heaters using hard water; none lasted throughout the entire testing period.  At some point in the testing period all of the water heaters using un-softened water were removed from the test due to inadequate flow caused by mineral deposit build-up in the pipes.

The on-demand gas water heaters operating on hard water had an 80% factory energy efficient rating. These units were allowed to operate down to a 72% energy efficiency before they were shut down for maintenance.  Maintenance required de-scaling of piping before being put back into use.  Once de-limed, the units only recovered a 77% efficiency rating.  The equivalent of 26 gpg of water hardness would require the on-demand water heater to be de-scaled every 1.6 years to maintain operation.   On-demand gas hot water heaters will lose their energy efficiency rating within the first year of operation proportional to the amount of hard water minerals present in the water.  A conservative estimate would be 10% efficiency lost in the 1^st 2 years of operation with hard water (Martin, David H.; Water Conditioning and Purification journal; 2010).

The gas storage water heaters operating on the hard water had a 70.4% factory energy efficient rating. These units were allowed to operate down to a 67.4% energy efficiency performance level before they were shut down for maintenance. Maintenance required was de-scaling of piping before being put back into use.  The maintenance schedule was estimated to require the field equivalent of service every 2 years of operating on 26 gpg of water hardness. The average rate of scale buildup in the gas storage tank using hard water was 1.16lb/year compared to 0.01lb/year of scale deposited in the gas storage water heaters operating on softened water.

The electric storage water heaters operating on hard water had a 93% factory energy efficient rating. These units did not lose energy efficiency in heating the water during the course of the test.  Since the heating elements are completely submerged in water, all heat is transferred from the elements to the water in the tank.  The maintenance schedule was estimated to require the field equivalent of service every 1.25 years in operation on 26 gpg of water hardness in order to maintain the water flow.  A shorter life span of the heating element was projected over a 15 year service life.    Scale build up still occurs; it just does not impede the energy efficiency of heating the water only the flow.  The average rate of scale buildup in the electric storage tank using hard water was 2.00lb/year compared to 0.03lb/year of scale deposit in the electric storage water heaters operating on softened water.

The Executive Summary, in citing a decrease in the carbon foot print when using softened water, in my judgment is misleading.  Since energy calculations are based on factory energy ratings (assuming low mineral water content) then the units would be performing as expected when operating on soft or low mineral water.  The warning should be that when using gas on-demand hot water heaters or gas storage hot water heaters with water containing hard water minerals the result will be an the increase in carbon emission because the performance is now below the efficiency rating from the factory.  A miscalculation by energy raters could occur if the water quality is not accounted for in the energy consumption estimates.

Key point to remember:

• Energy efficient water heaters do not automatically mean they will operate energy efficiently.   The manufactures set protocol for water quality and water quality test need to be performed and analyzed to insure the parameters for operation have been met. 
• There is a lot of controversy about water softeners today regarding the use of salt and a routine need to regenerate and backwash the softeners which results in water down the drain. These water conditioners are perceived as harmful and wasteful to the environment.  And many policy makers and concerned environmentalist perceive these salt base softeners are not helpful.  Therefore the Water Quality Association has invested in studies to understand how hardness is harmful to the performance of heating equipment and look at whether water softeners benefit home owners in energy conservation. The Battelle study does show that removing hard water minerals prior to heating water does prevent additional carbon emissions into the atmosphere.
• Consider the efficiency of a water softener based on these general softener settings for a family of 4 using 2000 gallons of water in a week for personal and household use. Plus another 140 gallons to backwash and regenerate the water softener once a week.   This ratio of 140:2000 offers a 93% water efficiency.
• Water softeners are more efficiency when operating with a digital demand controller compared to a time clock controller.  
• Human tendency is to assume clear water is good water and common tendency is to get our water “fixed” when it looks bad, but looks are deceptive and only water analysis for specific concerns will yield a better understanding of the water quality.
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Solutions:

• If you are on a well get a water analysis to understand what if any problems your water might present in consuming and using.
• Weigh the advantages of water conditioning if a water analysis indicates 3 gpg of water hardness or greater present in your water and you are operating or planning to use an on-demand hot water heater.
• Consider an electric hot water storage heater for use when hard water minerals are present in your water to retain the energy efficiency.

• Explore alternative means for dealing with hard water minerals to see if their operational parameters are appropriate for the impurities and quantities present in your water.

For additional questions regarding your water quality call or email ed@filtersfortap.com.

Edward Cortright BS, CWS, member of WQA and WNCGBC, owner of Filters for Tap and has 30 years experience in the residential building industry.