Instantaneous water heaters, best practices, watch out fors, etc

[lordofthepipes]

i usually talk people out of going tankless, or when i tell them that i have to do a gas load calculation and determine the demand of hot water to the home, test the water, and it will not be "free estimate" they say " ill call you back". truth is you usually need to either increase the gas line from the meter or run a separate line just for the TWH from the meter.repipe the water and the vent. most homes need the 199,000 btu modle and you are taking out a 40,000 btu WH. then it is recommended that a water softener b installed if you have hard water. hard being only 9-12 grains hard otherwise the homeowner needs to flush the unit annually with vinegar (yeah right). if they have a big tub with a roman tub faucet or a shower system you better figure out the load.i try to steer them to a hybrid unit like the polaris or the vertex. both have like 96% efficiency, can usually use the existing gas line,and put out a ton of hot water.

[Hyper48fan]

I posted this in another thread but I thought it would be nice to have it here as well.

Last week I responded to a call where my company had installed two Stiebel Eltron tankless water heaters (I don't recall what model)at a brand new car dealership. The problem was there was no hot water. Each w/h was installed under a counter top with two lavs, each equipped with Sloan proximity sensor faucets. I checked for voltage inside the unit and it was good. What I noticed was that with one faucet operating the water stayed cold but with two faucets operating the water got hot. I pulled up the Installation manual on my Samsung Galaxy Tab and found that with too low of flow it won't kick on. So I had to order 4 new aerators at 2.2 GPM because the Sensor faucets come with .5 GPM aerators. I hope this works, I'll let you guys know, I install them tomorrow.

[Hyper48fan]

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[Hyper48fan]

Today I installed the new 2.2 GPM aerators and adjusted (increased and decreased) the flow control to no avail. The threshold for the w/h was right at .5 GPM, so the .5 GPM aerators were just under that threshold. Once I installed the 2.2 GPM aerators I went way above the threshold and had too much flow, and when I cranked down the flow control to reach a consistent hot temp there was hardly enough flow to reach the edge of the sink.

SOOO, what I did was cut the screen on the backside of the .5 GPM aerators and pulled out the o-ring inside. That bumped me over the threshold and I was able to decrease the flow inside the unit. Now it works. The adjustments needed to balance this system were so minute that 1/32 of a turn either way was too much.

The model of the w/h was a: DHC 6-2

[Caduceus]

Reminds me of an experience with some Eemax units a few years ago. Should take so much effort and improvisation to get it to operate normally.