Proper pressurized well tank sizes?

Old 08-22-17, 06:10 PM
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Proper pressurized well tank sizes?

I've got a house where both the well pump and lake pump cycle on and off a lot. I think the tanks are undersized. The house has a well approximately 100' deep. I don't know the submersible pump size. The tank is a 20 gal pressurized well tank. It takes 19 seconds for the pump to cycle off once it comes on with no fixtures drawing water. The house has 5 toilets, 5 showers, 9 sinks, 3 spigots, dishwasher and a washer for a total of 24 fixtures. It's a tankless hotwater heater. What size should the well tank be? I've found one website that says to multiply the number of fixtures by 3 to get the minimum tank size. In my case, that would be 24 x 3 or the next size up from 72 gal. Other websites call for the pump size to calculate the tank size but I don't know that. What is the proper tank size?
I also have a a lake intake with a 1 HP jet pump that feeds 2 spigots to runs 1 to 4 sprinklers. The lake to pump height is less then 10'. It currently only has a 3 gal tank. Not surprising the pump only cuts off for a very short time before it comes back on. What size pressurized tank should it have?
Old 08-23-17, 03:09 AM
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Do you have an idea of what the recovery rate is on your 100' deep well (often expressed at gallons per minute - GPM), or where the pump is located relative to the static water level ?

That may play a role because you don't want the pump cycles to be longer if the result is that they exceed the recharge rate down in the well.

Bigger isn't always better.
Old 08-23-17, 05:48 AM
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Is your lake pump and pressure tank somehow related to your primary question?

Your current tank only holds about 8 gallons of water. So, a bit less than that is what you can use before the pump turns on. That is quite small for a house with so many fixtures.

The pressure tank does not pump water. It does not pressurize water. All it does is store water, smooth out the flow/pressure, and prevent the pump from cycling on and off quickly when water is being used. In your house the pump may be turning on and off very frequently when two people are showering at the same time. A larger tank would reduce how often the pump needs to turn on and off which will extend its life.

For a house your size I'd be looking at a 70-80 gallon size tank. They are much larger than what you have now so you might not have physical space in which case I'd get as large as will fit.

There is one downside to having a large pressure tank. In winter when you get that really unusual cold spell and are worried about your well or the pipe leading to the house freezing you might normally leave a faucet running to keep the water moving. A 80 gallon tank has a storage capacity of about 35 gallons. Running a faucet slowly could take hours to drain the tank and turn the pump on. By that time things may have frozen.
Old 08-23-17, 09:15 AM
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The other thing to do is to check how much air you have in your current and any new pressure tank, at regular intervals. If your air charge escapes from your pressure tank, then the amount of water it will give you will also go down. Whenever you have your tank empty you should take the time to check the air pressure to ensure it is still 2 or 3 psi below the cut in pressure of your pump.

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