Tankless water heaters? Quiet as a church mouse

Dec. 6, 2013
You need to be a mechanical detective Church mouse? More like a rat’s nest Let’s take a look at the Btus being wasted 140°F is not a safe delivery temperature to points of human contact

Working for churches is an interesting journey: property committees come and go, and, often, that means so do you if the new chairperson has an established relationship with another plumber! When you have that first chance to bid a project, you need to be a mechanical detective to sort out the myriad ways of others before you have creatively bent the mechanical systems to their individual tastes. Btus are wasted in huge quantities in most churches: escaping as quietly as the proverbial church mouse. This case was to be no exception.

“We want you to bid installing a tankless water heater for our kitchen.”

Sounded simple enough over the phone and it is a very large multi-story church that takes up most of a city block. The kitchen was expansive with sinks on three of the four walls with an old commercial dishwasher in the center.

“We will need 140°F water to the dishwasher because it has no booster heater.”

Their chosen location for the natural gas tankless water heater was on an exterior wall (safe venting of flue gasses – check √), over a 1.25-in. gas line (sufficient gas volume? √), but only a ½” cold water line was feeding the nearby sink (No √ for you!). Three commercial sinks and dishwasher required a study of the potable water distribution lines below the floor.

“We also have a DHW recirculation system that will need to be modified to eliminate the kitchen, but maintain the loop’s integrity for serving the numerous bathrooms.”

Church mouse? More like a rat’s nest where the conglomeration of galvanized, brass and copper water lines were concerned running through what bordered upon being catacombs. Ghosts of plumbers long having moved to the other side of the lawn no doubt were watching to see if the spaghetti could be untangled. Tracing lines revealed more than a few dead legs that were left behind: “We’d like them removed too.”

On to the mechanical room! The carcasses of two huge cast iron steam boilers lay strewn about the floor. The breech their flue pipes had made into the masonry chimney was sealed with a very large cement-patch and the 4-in. galvanized flue running its angled width across the large room revealed the water heater was behind the door. Gas fired 75-gallon residential model set to maintain that 140°F the dishwasher required. Do you have scald-guard mixing valves at the various points of human contact? “No. Should we?” Two 87-watt wet rotor circulators: one bronze; the other stainless steel, were controlled by a timer and that led to tracing both recirculation lines, which provided a tour deep into the recesses of the church’s catacombs. Do you have a gym and/or any bathing facilities? “No, just the bathroom sinks and kitchen use hot water. We know we’ll save money by installing the tankless and turning down the storage temperature for this water heater.”

Good grief!

Let’s take a look at the Btus being wasted and the safety issues:

  • They have somehow avoided any reported scalding incidents and there is a nursery room where children have access to sinks as well as a large constituent of elderly worshipers. Infants, children, and the elderly scald much more easily than do others. We plumbers bear responsibility to provide advice regarding scalding. (√)  
  • Two circulators at 87-watts each using around 635,100-watts annually = $76.21.
  • DHW lines (both the supply and return) running hundreds of feet at 140°F = approximately 45,000-Btus silently escaping per day, which has to be divided by the .63-EF (Energy Factor) of the water heater and that = 71,429-Btus. Roughly $260 wasted each year.
  • They’re turning the DHW recirc system OFF for half of each day’s 24-hour cycle. More advice required regarding Legionella bacteria. (√) With the kitchen load on the DHW system about to be gone, there’s no real need for the gas tank-style water heater or, for that matter, the remainder of the hundreds of feet of DHW piping. With the limited and infrequent use of DHW at the spread out points of use, small tankless electric water heaters make perfect cents! Take advantage of the opportunity to serve as an energy conservation consultant? (√)
  • The existing cavernous masonry chimney was now serving just the orphaned water heater. Unless a liner was installed in the three-story-tall chimney, this was a sustained flue gas condensation situation in progress. When fossil fuel water heaters are orphaned in masonry chimneys, danger often lurks: http://contractormag.com/hydronics/orphaned_heaters_719. Once again, we plumbers shoulder the responsibility to educate and advise our clients. (√)

Their commercial kitchen was more than suitable for justifying the installed cost of a tankless water heater. Sizing for the maximum DHW draw required a 240,000-Btu model because the 140°F cannot be compromised if food-bacteria-laden dishes are to be sanitized and 140°F is not a safe delivery temperature to points of human contact. The simple solution is a two-pipe DHW distribution system with an ASSE listed (meaning it has been tested by an independent lab) 1070 scald-guard thermostatic mixing valve for the sinks’ distribution line. http://www.watts.com/pages/learnAbout/temperingValves.asp?catId=   

As for the rat’s nest of piping? A home-run manifold also made perfect cents!    

All Dave Yates material in print and on Contractor's Website is protected by Copyright 2013. Any reuse of this material (print or electronic) must first have the expressed written permission of Dave Yates and Contractor magazine. Please contact via email at: [email protected].   

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Dave Yates

Dave Yates material in print and on Contractor’s Website is protected by Copyright 2017. Any reuse of this material (print or electronic) must first have the expressed written permission of Dave Yates and Contractor magazine.

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