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Diving into the deep end of a plumbing spa issue

May 11, 2017
Before diving into the deep end, here is just one of the many issues we discovered in 2005: Two 82 percent efficiency tankless water heaters were not vented in compliance with the manufacturer’s requirements. The flue piping used is galvanized and the manufacturers literature specifies stainless steel be used. 
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You know your day is bizarre when it’s necessary to wear a bathing suit to check for problems with a customer’s plumbing! There were a host of problems already discovered on this job. One final issue — flooding to the basement below needed an answer for this single homeowner, and she was quite insistent we determine the cause.

Before diving into the deep end, here’s what we discovered in 2005:

PRV (pressure reducing valve): Measuring the flow, we were seeing a 2.2 GPM flow rate, which indicated the PRV was not functioning properly. We checked its inlet strainer, which was not clogged and noted that the pressure-adjusting screw had previously been tightened all the way down to allow the maximum amount of pressure delivery. This adjustment would tend to indicate the previous occupants had experienced pressure problems as well.

The PRV was replaced, which resulted in an immediate improvement of flow within the shower area. Retesting revealed a static pressure of 80 PSI (with adjusting screw midway in its adjustment range — a typical location for a properly functioning PRV) at full flow (with all shower valves engaged) pressure drop off of just 12 PSI, which when compared to the manufacturer’s chart for the new 1” PRV matched our timed/measured flow rate of 14.5 GPM.

Two tankless: Two 82 percent efficiency tankless water heaters were not vented in compliance with the manufacturer’s requirements. The flue piping used is galvanized and the manufacturers literature specifies stainless steel be used. Additionally, as the manufacturer’s letter indicated (sent to the previous owner), each heater must be equipped with a back-draft damper to prevent freeze damage. Both had suffered a loss of the heat exchangers from freezing during the first winter, yet the venting was not corrected.

The two tankless water heaters serving the shower had different Btu inputs. They were installed in parallel with no flow regulation to govern their output for balancing. A PVC flow-check (PVC plastic is not rated for high-pressure hot water usage) was installed in the CPVC hot water distribution system between the two tankless water heaters to facilitate hot water usage at the lavatory faucets.

The check-valve isolates the hot water draw at the lavatory faucet to just one of the two tankless units. A .75 GPM flow rate is required to initiate burner operation, which would have required 1.5 GPM of flow in a balanced-flow parallel application where both tankless units “see” the water usage. Faucet aerators are required to be limited to 1 GPM (federal mandated guidelines for water conservation), which would have made it virtually impossible to trigger the burners if both saw just a portion of a 1 GPM flow rate.

During use of the shower modules, flow through the smaller tankless was 2.8 GPM while flow through the larger model was 3.8 GPM for a total of 6.5 GPM at 111°F. Temperatures fluctuated quite a bit upon initial start-up and when various bathing faucets were activated within the shower area. Delivery temperatures of 120°F were observed, which resulted in hotter-than-comfortable delivery temperatures until the heaters settled in on their new flow rates and maintained the 111°F setting.

Well water expansion tank: A large expansion tank, typically found in well water systems, was installed under the shower area and tied into the domestic potable water system. No doubt this was an attempt by the previous owner to fix the low delivery pressure from the defective PRV. Given the 15 GPM flow rate at any one of the three high volume shower faucets would deplete the stored pressure rapidly.

So, why the bathing suit?

This walk-down-into bathing/spa area had one unique feature. The shower/spa area had —  in addition to the overhead rain shower head, sunflower shower head, a wall of body jets and hand-held shower wand — a Kohler 80 GPM ten head waterjet tower! The walk-down-into “pool” was designed to be filled to a depth where the pump’s suction strainer would be submerged, so that it wouldn’t draw in air during its operation. The minimum level required was to the top of the first stair tread, which required slightly more than 211 gallons of water be introduced and held within the shower basin.

Upon activation of the shower tower and its 80 GPM pumped flow, the jets discharged water that traversed the 80” span to the opposite wall and directly impacted the cover plate on that wall’s shower valve. This immediately resulted in a considerable amount of water leaking down through the wall cavity and into the basement as reported by the other employee with me (no way I was going to be traipsing about in a bathing suit in a customer’s home without bringing another plumber with me)! Telltale stains on the framing and plywood below indicated this has been an ongoing problem. Faucet cover plates are not designed to be leak-free when directly impacted by a head-on flow — especially one with such force.

Water temperature within the recessed floor basin quickly lost its heat to the surrounding masonry products and even more rapidly once the recirculating system was activated. Although we were receiving water that varied from 99°F to 110°F at the various shower heads/jets, the temperature within the 211 gallons had dropped to 87°F by the time we could attain proper depth. That dropped off to 83°F following five minutes of shower-tower runtime. Kohler’s catalog lists the ten jet system as including an integral heater. However no heater could be located during our inspection.

Distressed and angry would sum up the owner’s feelings. “But, I had a certified home inspection,” said the homeowner.

Let the buyer beware! She subsequently sold the home to another unsuspecting owner who called in a general contractor, who called me and started telling me about the walk-down-into spa area. Nothing has changed except for two newer tankless water heaters now serving the spa bathing area.

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. Please contact via e-mail at: [email protected].         

About the Author

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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