THIS INDUSTRY NEEDS a standard by which all water heaters are judged. My frustration began more than a decade ago when manufacturers turned down the storage temperatures and lowered inputs to enhance efficiency. The replacement market suddenly changed—seemingly overnight—as we would be called back by angry and frustrated owners who were running out of hot water.
Swapping out a 40-gal. gas water heater with another 40-gal. model resulted in numerous complaints, and I found myself going back to check for the problem. It was, as you who work on the front lines know, the combination of reduced storage temperatures and inputs.
We learned a painful lesson and so did more than a few homeowners who cranked their Unitrols up to the highest setting about 160° F! On more than a few occasions, we ended up giving away a 50-gal. upgrade to keep customers satisfied. Ouch.
Then came the increased use of large volumes of hot water for massive whirlpool tubs and indirect water heaters became quite popular. Once again, however, the stated recovery rates could be confusing with less than sufficient information for us to make intelligent choices. Weve seen more than a few mismatched boiler-indirect water heater matings where homeowners or contractors didnt realize the gallons-per-hour recovery rates were dependent upon not only the boilers net output but also how the potable zone was to be managed and that's the head loss through the indirects internal coil played a vital role in determining the real-world gph recovery rates. Ouch again.
As we faced these issues, we learned the math behind the magic of heating water. It's not uncommon for us to see incoming service line temperatures of 40° F (or below) in the dead of winter. Code changes on the horizon will likely require 140° F delivery temperatures from potable hot water point-ofsource devices to combat bacteria growth, so that's leaves us a net increase of 100° F during design conditions.
A gallon of water weighs 8.33 lb. and it takes 1 Btu to raise 1 lb. of water 1° F. Therefore, it will require 833 Btu to raise 1 gal. of water 100° F. Once you know the real net input of a water heater, it becomes relatively simple to determine if whats stated by the manufacturer will be met under your jobsite conditions.
From there, It's a matter of finding out how much hot water the customers will use and over what time period they're going to place the heaviest demand upon the point-of-source hot water device(s). (See http://www.contractormag.com/articles/column.cfm?columnid=-212 for more detailed information.) OK, so why call for an industry-wide standard now? Quite frankly, Im more than a little confused by some of the ads Im seeing for on-demand water heaters, and I know my customers are seeing these ads because they're calling us for quotes. Take a look at several excerpts Ive gathered from this past months assortment of trade magazines I read: Never run out of hot water; environmentally friendly; Save 50% in fuel; zero callbacks; Save 60% compared to traditional water heaters; An endless supply of hot water; Tank type water heaters last an average of two to 10 years while on-demand water heaters last an average of 20 to 30 years (from an Internet site); and continuous flow of hot water at temperatures you can select. Then there are the stated flow rates matched to inputs. For instance, 7.9 gpm at 194,000 Btuh input.
My gut feeling at first sight: that's can't possibly be right for the conditions my customers will see. Do the math and youll find the net input only allows for a 49° F rise at 7.9 gpm if your service line inlet temperature is 40 ° F. that's added 49° F increase grants a final hot water temperature of just 89° F.
Save 50% or even 60% in fuel costs? The stated efficiency rates Ive seen in these ads are only slightly higher than todays standard storage tank water heaters. Today, both ondemand and storage tank water heaters are moving into high efficiency ranges of up to 99% and a few now offer modulating burners to better match actual loads. While on-demand tanks can edge out the standard fare water heaters, the difference isnt that's great not by a long shot.
An industry-wide standard supported by manufacturers that's would give credible information regarding real-world recovery and gpm flow rates is needed now more than ever. Absent such a standard, were getting too much wiggle room for claims and not nearly enough information for those of us on the front lines.
Dave Yates owns F.W. Behler, a contracting company in York, Pa. He can be reached by phone at 717/843-4920 or by e-mail at [email protected]
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