Atypical Water Heater Configuration

(Chuck Evans, CMI TREC 7657) #1

I inspected an 11,000+ square foot house yesterday that had a water heater setup that I had not encountered before. It had a pair of 199,900 BTU/hr tankless units installed conventionally on one area of the house, but the other installation paired a similar tankless unit with a 6 gallon 120v electric tank type unit with a circulating pump. The electric water heater was plugged into power.

What would be the rationale for supplying power to the electric water heater or even having it in this configuration? Does the rate of flow from the circulating pump not activate the flow switch on the tankless unit unless there is demand? I’ve seen tankless systems with circulating pumps, but not combined with a live electric tank unit.


(Roy D. Cooke, Sr) #2

Sounds like a large home and it takes a long time to get warm water to the taps .I expect this system gives them hot water almost instantly to all hot taps .


(Michael Larson, WI Lic. # 1672-106) #3

Think of it as a buffer and a source of higher flow.

I bit unconventional but I could call the original installer and see if they would provide a better explanation.

Not a defect but I would be curious too.


(Emmanuel J. Scanlan, TREC# 7593) #4

That appears to be a Grundfos Comfort System series pump with a timer. They have an approximate 6 GPM flow rate with almost immediate max flow when activated. The Rinnai WH only requires <1 GPM flow to turn the burners on and around .25 GPM flow to keep them on.

The only possibilities I would think of is to have a ready source of hot water during the timer off times until the WH kicks in. It could be enough to warm the path until the tankless flow is in the line. Also that Grundfos pump has a 36 - 150 Degree F operating range. Your Winter design temps have been set at 28 Degrees in your area. Being in the attic I would expect they could actually reach that low and long enough to damage the pump. Having the tank running would provide a ready source of hot water (and heat) to prevent that. I see they foamed the attic but is there a source of conditioned air there? Did the plumbing go in before the Plumber knew it would be foamed? Was the foam application correct and the outer envelope sealed properly? I’ve seen them foam attics and screw up with penetrations to the exterior.

It would be interesting to have the installer take on why they did it or even one of our own Professional Plumbers on the board chime in.


(Barry Adair, TREC#4563 EIFSTX#39) #5

(Emmanuel J. Scanlan, TREC# 7593) #6

Good stuff Barry!! Don’t want to anger Mom do we? :wink:


(Larry Kage, CMI) #7

Barry’s the man! Thanks for the information sought. :smiley:


(Chuck Evans, CMI TREC 7657) #8

Thanks, guys.

I’m very familiar with using circulating pumps to minimize wait time for hot water in large houses, but this was the first I’ve seen a tankless unit paired with a tank type water heater.

Barry - You nailed it. I googled it but didn’t get a hit, so you obviously did a better job with keyword selection. Thanks!

Manny - The house was built in 2014 and was designed with an unvented attic assembly (like everyone else, they forgot to ventilate the garage attic, though they did isolate it). It only had four HVAC systems all HE condensing type, along with the primary water heaters, but you’ll note that they forgot about insulating the hot water lines with the circulating pump. It was an interesting place with high-end home automation features. I could control all of the thermostats from a central control panel near the kitchen. The actual thermostats all had remote sensors and were clustered in a closet in the second-floor laundry room. Property taxes are a mere $75K/year.


(Barry Adair, TREC#4563 EIFSTX#39) #9

hey Chuck
close plmb friend, prior encounter, saved docs w/link for future & dyslexia help
hope you & yours are thriving!


(Dave Fetty, CMI) #10

Great thread… thanks guys!


(Chuck Evans, CMI TREC 7657) #11

Thanks Bear. I still learn something new every day.

We’re doing great. Prepping for a big move soon.