Thermal expansion tank question

Based on a prior thread, I have determined my w/h needs a thermal expansion tank, which I'm capable of installing myself. I found a tool online that helps determine the size required for any given application, but I wanted to double check this with you professionals. The tool asks for the following info, with my inputs in parentheses:

Water Heater Gallons (50)

Supply Pressure (60 psi)

Air Pre-Charge 40psi Air Charge is Standard. Never exceed 80psi Pre-Charge. (I have no idea, so I left it on the 40 psi default)

Relief Valve setting (150 psi)

Initial Temp-Start (default again, 90F)

Final Temp-End (120F as measured at a faucet)


This gave me a Calculated Acceptance Volume of 0.3 gallons, and a Calculated Total Volume of 0.82 gallons.

I was referred to a chart that showed the following technical data for a tank that the tool said should work for me:

Description DET-5-M1
Max. Pressure - PSI 150
Max. Temp. - °F 200
Tank Volume - Gal. 2.1
Tank Acceptance - Gal. .85
Air Pre-charge - PSI 40
Connections Size - Inches 3⁄4 Male
Diameter - Inches 8.5
Length - Inches 11.5
Weight - Lbs. 7

Is it really this simple? Can I take this info to my neighborhood Home Center with a plumbing department and get a suitable tank? I realize we can't discuss brand names here, but how do I know I'm getting a quality product that meets these requirements?

Anything else I should be aware of?

Thanks! Mike

get the big one

dont fool around trying to calculate wether the little one will
do the job or not ,,,

just get the bigger expansion tank that you can buy and set it at about

70 psi.... about 10 lbs higher than your water pressure and you
will be fine....


we messed around withthe smaller ones for a while but found
that they could not take the stress as well as the larger one...

too much expansion and contraction and not enough volume....

and according to the scales they it just
barely did the job for a 40 gallon heater..
that is not good for the long haul....



and most of the information you will need comes inside the box.

If you take all that info to one of the big box stores or a home center they will look at you like a deer in the headlights and then blink a few times before they make up a story and sell you a large exp. tank.

Unless you live in the desert, your incoming water will be much colder than the 90-degrees you indicated, in my area, in the winter, it is more like 35-degrees. Water gets denser as it gets colder until it starts to freeze (that's why it floats - which in the scheme of things is very strange but lucky for us). SO, if you ran the numbers using a colder supply, you would need more volume.

jadnashua said:

Unless you live in the desert, your incoming water will be much colder than the 90-degrees you indicated, in my area, in the winter, it is more like 35-degrees. Water gets denser as it gets colder until it starts to freeze (that's why it floats - which in the scheme of things is very strange but lucky for us). SO, if you ran the numbers using a colder supply, you would need more volume.

Click to expand...

JAD, I thought that was strange, too, but it was the default used by the tool, with the following caveat:

Initial Temperature - Start *
NOTE: Set the cold water start temperature to 90°F. Lower start temperatures should only be used if the entire contents of the water heater are drained on each use.

The tool I refer to can be found at:
http://www.watts.com/pro/divisions/watersafety_flowcontrol/support/support_DETsizing.asp

My initial temp this time of year is also around 38-40F. So between your answer and Mark's, I think I'll go with a larger than recommended tank.

Thanks!

WIth teenagers, you are likely to drain the tank...bigger is better. My tub needs 45-gallons, but obviously, that is not all fully hot water. Throw in the washing machine doing its thing, and maybe the dishwasher, and it isn't hard to empty most tanks.

I agree that if you have room for the bigger one, it certainly won't hurt to go with it. However, the small one will work fine.


Box stores will have two sizes, small and large. Install it on the cold side downstream of the shutoff. DO NOT use the saddle clamp attachment that comes with it if you get it at the box store.

A reputable plumbing company just installed a new Uponor PEX-A 1-inch main water supply line to my residence with an Aqualine PRV. The city came by and red-tagged the job. The inspector refuses to close the permit. Apparently, I need a thermal expansion tank before the inlet to my water heater. The water heater is 50 gal. set at 125 (but could be set higher in the future--it's summer). See pics below. Pressure from the water meter in my neighborhood runs about 120 psi. PRV is set to 70 psi (it's adjustable). The inspector also told me cryptically that there are other (?) problems with my water heater installation. I never knew they would be looking in my garage when work was completed in the front yard.

From this thread, it appears that I should install the largest possible thermal expansion tank within reason, right? I've used some calculators and came up with the following models:
Amtrol ST-12 Therm-X-Trol Expansion Tank
Watts PLT-12 Potable Water Expansion Tank
Zurn Wilkins XT-18 Thermal Expansion Tank

Setting the tank at 10 psi higher than my current PRV setting/current water pressure will be 80 psi. Is that too high for these tanks?

Thank you for your time and help.

Sterling

Watts and Zurn Wilkins set the maximum permitted precharge to 80 PSI. Amtrol Therm-X-Trol does not set such a number. They each permit the pressure in use to hit the 150 PSI where the T+P valve opens.

Precharge must be set with the water pressure zero. Set the air to the PRV regulation pressure to a couple pounds higher. So I would set yours between 70 and 72.

Amtrol's Therm-X-Trol is the top brand. It calls for the fitting on top. I think the other two permit any orientation, but need support if the tank is not vertical.

Cryptic-problem-wise, it looks like you have 3/4 copper for the discharge pipe. Technically 3/4 copper is not big enough, using a very strict interpretation. 3/4 IPS is big enough, and it is the only good use of galvanized pipe in a house today. Using 3/4 copper is usually permitted in practice, and even 3/4 CPVC is allowed in some areas.

Those black supply lines are not the best. Corrugated stainless or copper is better. If you see black particles in your hot water later, it could be the supply lines.

He may not have liked the humidifier supply line.

Saddle valves are a problem waiting to happen. That's what it appears you have feeding the humidifier. When sizing an ET...it is assumed that you precharge it to the static water pressure. That puts the diaphragm at the 'neutral' position, and allows it to perform as designed. Overcharging it will prevent it from moving until the pressure gets at least that high, and puts more stress on the thing. Undercharging it means that it will normally be partially full, decreasing the available expansion volume, and constantly applying pressure/stress/stretch on the bladder.