I am replacing the dip tube in a HW tank. I bought a generic dip tube, which is (of course) longer than necessary and must be cut. How far from the bottom of the tank should the bottom of the dip tube be?

I looked up the dip tubes sold by the manufacturer. The original was 34", now discontinued. The replacement is 36.5". I have no idea if these lengths include the metal nipple length or not. I suspect they do. (A change in nipple length might account for some of the change in over-all length. But I also am suspicious of the "replacement" - was the length changed because they decided 36.5" was a better length than 34", or because they were already making one of 36.5" for newer models, and that length is good enough, lets save costs?)

But 34" measured from the top of the nipple v.s. 36.5" measured from the bottom of the ( 3" ) nipple is quite a difference: 5.5". 36.5" from the bottom of the nipple puts the bottom of the dip tube only 1/2" from the bottom of the tank, v.s. 34" from the top of the nipple which yields a 6" space to the bottom of the tank.

I read somewhere that the dip tube should only come 2/3 of the way down the tank, so as to keep the insertion point of the water a good distance from the thermostat. This does not make a lot of sense to me - if there is cold water coming in, do you not want your thermostat to sense this and fire up the heater? (Seems to me a 2/3 length dip tube would introduce huge hysteresis.)

Thanks.



Edited 4 times.

6 inches is fine

for what it's worth:

Quote

A typical dip tube attaches to the cold water inlet of a heater and runs up to roughly 8 inches of the bottom of the tank.

It is a long plastic tube that brings in cold water and pushes it to the bottom of the tank, where the gas burner or any other thermal device heats the water. The dip tube is also responsible for preventing cold water from mixing with water that’s already been heated.

IMO: 4-8" is just fine

Back in 1953, Rheem/Ruud sent their gas heaters out with "overlength" dip tubes, were just above the tank bottom.. They were rigid and very expansive. Over a very short time they would push up through the cold nipple, impact the galvanized union connecting the tank, collapse the end a bit, then expand some more and collapse again. After a few times, it would look like a soda straw that someone had pinched closed and reduce the flow to almost nothing. We had to cut the tube flush with the nipple, the drive the lower section down into the tank and install a new copper tube..

@hj (AZ). Wow, this is exactly what the nipple on mine looked like when I replaced it. But it dated from 2010 only.