I am finishing a guest house next to my house. The two houses share the same pressurized system from a well pump near the guest house. Previous owners did not put a pressure tank in the system at all, just 3 thermal expansion tanks.

I am setting up a pressure tank for the first time and while I believe I have it covered pretty well I am hoping to get confirmation, as well as consideration of 2 different plans.

I have a 1" PEX in from the well pump that will hit a 1" check valve, then a small tee to the well pump control pressure sensor, then a 1" ball valve. It will then run about 7' to where I've decided to put the tank. The tank tee will have a drain bib, a pressure release valve, and a gauge. The tank tee is a 1 1/4" so I'll have to expand to it then either:

a) cap the other end of the tee and let the tank be a 7' dead end. (the 3/4 guest feed will have a shutoff valve, forgot to draw it in) enter image description here

b) reduce it down to 3/4 after the tee and run it 7' back in order to have the guest house supply flow through the tee. enter image description here

In addition to this a/b option I am wondering if there is a problem with expanding a 1" inlet to 1 1/4" to feed the tank? I understand that the responsiveness of the tank will be limited to 1" for the shared system, I am just not sure if there are other issues I haven't thought of.

For inquiring minds: I don't want to put the tank closer to the inlet because I'd have to trade places with the WH. If the tank distance is ok, I'd prefer leaving the WH closer.

I am looking at a 1 1/4" tee because that is what the 44g tank I am planning on getting is.

Thanks for the thoughts.


2 Answers 2


Your diagram doesn't show exactly where the main house is getting its supply, so I'll assume that there's another tee somewhere.

The pressure tank will do its job no matter where you tee off the supply for the guest house, provided that it's beyond the check valve. So tee it off to the guest house at the most convenient point. Literally anywhere. Doesn't matter.

There's another answer here that says, "water flow to the guest house will bypass the tank" but that fails to recognize that the static pressure is the same at all points in a water system, except for slight differences due to altitude (head). The "bypass" concept is like saying that a pressure tank will help for the kitchen sink but not for the bathroom. Not true, it's all one plumbing system, it's all connected, it's all at the same pressure and there is no bypassing.

Changing from 1" to 1-1/4" for the tank is no problem.

I do have one objection to your layout though.

It is best practice to have the well pressure control right there at the pressure tank. Check installation instructions for both the control and the tank, and you'll see that they both say so. That's why you can buy a complete pressure tank installation kit that contains everything in one unit: the Tee with additional ports for the pressure switch and a gauge, a drain valve, a pipe to go to the tank and a pressure relief valve. Keeping the switch as close as possible to the tank maximizes the pressure stabilizing effect of the tank and helps to eliminate short cycles.

Remember that the first shutoff valve after the well (except for a check valve) must be after the pressure switch / tank combo. A shutoff valve before the pressure switch could allow the switch to turn on the well pump into a closed-off pipe, which could cause damage from too-high pressure.

  • Appreciate the input, wondering if you have thoughts on the 2 different layout options?
    – Rowabo
    Jul 15, 2023 at 20:42
  • 1
    @Rowabo As drawn, there is no practical difference in function. The guest house is the same distance from the pressure tank in either case, or nearly so. The short run of 1" vs 3/4" will have no practical effect.
    – MTA
    Jul 15, 2023 at 21:31

Setting up a pressure tank for your guest house's well pump system is a good idea to provide stable water pressure and reduce strain on the pump. Let's address your concerns and consider the two different options you mentioned.

Option A: Having the tank as a dead end: If you choose to cap the other end of the 1 1/4" tee and let the tank be a 7' dead end, it should function fine. The tank will still provide the benefits of storage and pressure stabilization. However, keep in mind that with this setup, the water flow to the guest house will bypass the tank, and the tank will only affect the pressure on the main line leading to the guest house.

Option B: Running the line through the tee: If you decide to reduce the size of the tee to 3/4" after the expansion and run it 7' back to have the guest house supply flow through the tee, it will allow the tank to directly influence the water supply to the guest house. This setup can be beneficial as it ensures that the water supplied to the guest house passes through the pressure tank, helping maintain stable pressure and reducing cycling of the pump.

Regarding expanding a 1" inlet to 1 1/4" to feed the tank, it should generally be fine. While the responsiveness of the tank will be limited to the 1" inlet size, expanding it to 1 1/4" shouldn't cause any significant issues. The main consideration is to ensure that the connections are properly sealed and secure.

One additional point to keep in mind is the capacity of the pressure tank. You mentioned considering a 44-gallon tank, which should provide sufficient storage for most residential applications. However, it's important to verify that the tank's capacity matches the demands of your water usage in the guest house.

Overall, both options are viable, and the decision depends on whether you want the tank to directly influence the water supply to the guest house or if you primarily want to stabilize the pressure on the main line. Whichever option you choose, ensure proper installation and follow the manufacturer's guidelines for the pressure tank and related components.

If you have any further concerns or specific requirements, it's recommended to consult a professional plumber or well pump specialist who can evaluate your setup and provide personalized advice based on your specific needs.Ascii representation

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