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Community and Q&A

Winterizing Pipes

lekawa | Posted in Mechanicals on

Any plumbers out there?

I’m wanting to drain pipes in new addition in case it freezes out there before there’s time to get drywall in and mini-split air handlers installed.

I have shut off new curb stop valve outside addition…
opened up main valve in the addition…
opened laundry valve…
opened hose bib valve…
and opened tub valve…(but there’s a cap on tub spout pipe)
there are also two (soon to be) sinks and one (soon to be) toilet with capped off pipes

My questions:  Is it necessary to remove remove cap to drain tub spout?
Is it necessary to blow out any remaining water in lines?

I’m told I “shouldn’t” have to worry about pipes freezing until at least early December (I guess that all depends)  I’m just wanting to play it safe and be ready for anything since I’m not yet sure when drywall and mini-split air-handlers will be installed.


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  1. Expert Member
    BILL WICHERS | | #1

    You need to blow out water that might be in any low spots or inside of valve bodies. In my personal experience, shower valves are especially critical (I had one freeze at a cottage some years ago, which we didn't find out until repressurizing the lines in the summer).

    You also need to put RV antifreeze in any drain traps to displace water with something that won't freeze.

    What I do is to open all the valves, then drain a low spot until water stops running, then I connect an air compressor near the water source and blow out each plumbing fixture in turn, one at a time. I then go back and repeat the cycle until no more water comes out and the pipes stop "gurgling". I then shut everything, including a secondary main shutoff just in case. In my case, I also have a water heater to drain (be SURE you shut of electricity or gas to the water heater first!).

    You typically start winterizing in the late fall. You don't really have to worry until temperatures get below freezing for a few hours each night. Little dips to just barely freezing (frost advisories) aren't usually a problem. It's the "freeze warnings" that indicate its going to get AND STAY cold for a while -- those are the conditions to watch out for.


  2. Expert Member
    NICK KEENAN | | #2

    I agree with everything Bill said and will add some details that I have learned over the years.

    You definitely want to blow the pipes out with compressed air. You need a compressor and this fitting:

    Regulate your compressor to 50 PSI so you don't blow something out. I like to use an oil-less compressor so I don't have to worry about introducing oil into the plumbing.

    You need to have a hose bib where the water enters the building, otherwise there's no way of getting water out of that section. This is where you want to attach your compressor.

    First, drain as much as you can by gravity. Open all the taps and flush all the toilets. If you have a water heater tank or other large container it saves time to use a utility pump to pump it out. A good one can even create a vacuum which helps pull water out of the pipes. Then close everything, hook up the compressor, and get it up to pressure. Close the shutoffs on the toilets. Starting at the compressor, work away and up, opening each tap until you get air streaming. If you have a mixing valve like a shower or sink, run it through hot and cold until both run clear. On a toilet open the shutoff until air bubble in the tank. When you get to the farthest away tap reverse the process, working down and in. I find it can be hard to get the water out of the second floor if you haven't already blown it out of the first floor, and vice versa. Then turn off the compressor, release the pressure, and open every tap and valve. Leave mixing valves halfway between hot and cold.

    Use a shopvac to vacuum any residual water out of every toilet, tank and bowl. I use a measuring cup to put RV antifreeze into every trap. I put 8 oz in a vanity sink, 16 oz in a kitchen sink, tub or shower and 32 0z in a toilet, washing machine or dishwasher.

    I remove all of the aerators from the sinks before blowing them. When you turn the water back on there tends to be all sorts of crud on the inside of the pipes that has dried and flakes off, it will clog the aerators. Blowing air will also loosen a bunch of crud.

    I find that if you don't blow out the pipes there can be nooks where water gets trapped, especially in valves. While it helps to leave every valve open to keep pressure from building, it doesn't take much to crack the case.

  3. lekawa | | #3

    Thanks for the detailed replies & info! I think it's helped me understand the whole system a little better and what I do and don't need to stress about.

    I spent a good chunk of time today trying to figure out what type of air compressor I would need (how many CFM) in order to blow the lines out. The standard recommended CFM is 20! That seems crazy to me. I can't even find a rental compressor with that many CFM in my area. I also can't easily open up pipes where the sinks and toilet and water heater will be installed (none of them are in yet and those pipes are capped off.

    I did call the plumber who did the rough-in and he has told me to cut the cap off tub spout pipe and drain it...and having already opened the hose bib valve, washer valves and shower valve to drain....he says that's about the best I can do and it "should be" fine for another couple of months. Maybe I'll just get a space heater in there depending on night time temps until I can get the drywall and air handlers in. I guess this just means the pressure is back on to hurry up and get these things done!

  4. Expert Member
    NICK KEENAN | | #4

    I've used this compressor with great success:

    You don't need that much flow, you're only opening one valve at a time. It may take a while to get the whole system to 50 PSI but then it should just be a quick blast of air at each fixture.

    Definitely cut the cap off of the tub. Just leave as much pipe as possible for when it's time to put the spout on.

    I wouldn't bother with a space heater.

  5. Expert Member
    BILL WICHERS | | #5

    You need volume more than pressure to blow pipes, and that does usually mean a big compressor. You can cheat and use a smaller compressor, but it takes more time. What I do is to let the small compressor pressurize the hot water tank with air to about 50 PSI or so. Once the compressor shuts off, I use the hot water heater as a big air tank to blast out the individual plumbing fixtures. When the blasting gets too weak, fill up the water heater with compressed air again. You can also just pressurize the pipes and then blast things, but it doesn't work as well as using a tank.

    I agree a space heater isn't a great idea. If you do go that route though, I recommend using a backup thermostat (you can get greenhouse thermostats intended to run space heaters). I had the thermostat weld on a space heater once that heated up part of my cabin a LOT and messed up some of the woodwork. With a secondary thermostat as a backup, you have two thermostats that can shut things off if needed.


  6. Expert Member
    NICK KEENAN | | #6

    If you can't drain or blow out the pipes you can use a utility pump to fill the pipes with RV antifreeze. This might work better with stubbed out pipes. If the water heater is already installed that's going to be a problem because it will take an enormous amount to fill it, unless it has shutoff valves on both the cold and hot sides. Otherwise it should only take a couple of gallons to fill a typical house.

    You still also have to pour antifreeze down the traps as noted above.

    An important note: The RV antifreeze that Bill and I have been talking about is not regular automotive antifreeze. It is a non-toxic chemical (propylene glycol) that is sold for the purpose of freeze-proofing potable water systems. Regular automotive antifreeze is highly toxic and can't come anywhere near plumbing.

  7. lekawa | | #7

    That sounds like a great idea!....and no, there's no water heater installed yet.

    That won't hurt pex pipe will it? ....and I assume it will flush right out once water is turned back on again?

    I just found a video made by the "This Old House" guys showing how to winterize plumbing and they mentioned this stuff...but because they were dealing with a finished house, all of the things they covered didn't actually apply to my situation..

    Next question what is a utility pump? Is this something I'll likely be able to rent?

    1. Expert Member
      NICK KEENAN | | #8

      I use this one:

      You can get a smaller one on Amazon for less than $50. You're looking for a "transfer pump" with garden hose attachments. You just have to make sure it has enough pressure to reach the highest plumbing. Fourteen PSI of pressure equals 32 feet of lift.

    2. Expert Member
      BILL WICHERS | | #9

      Propylene glycol won’t hurt PEX. PEX is actually pretty resistant to all kinds of things.

      Running water through the pipes in the summer will flush all the RV antifreeze out. Just run everything for a while to make sure it’s all flushed out of the system.


  8. krom | | #10

    most RVs and boats use pex plumbing. Buy glycol based rv antifreeze, not alcohol based.
    pour some into each trap (usually you can hear when it starts to run) into each toilet bowl and tank, and pump it into the plumbing lines after blowing them out

  9. lekawa | | #11

    O.k... Just to re-cap. The lines have been drained but not blown out....and I'm adding the anti-freeze "instead of" blowing out the pipes. There are caps on toilet pipes (no toilet yet) and also caps on water lines for both sinks (no sinks yet) and no water heater yet. The only valves that can be opened are hose bib, laundry and shower/tub. I had to cut the cap off tub spout pipe to drain it, so it's now "open" unless I were to cap it off again (don't know if the shower valve, in it's current state (no handle) can close off water into tub spout pipe...I'm guessing it can?)

    So if I pump propylene glycol (RV antifreeze) in from, say...the hose will possibly displace some of the water remaining in low points, or at least mix with it, providing "some" protection? I guess I'm wondering now whether the capped off pipes will prevent water from flowing toward them...or....maybe it doesn't matter if it does since the water seems to have drained down from them anyway...???....and because I'm mostly just trying to prevent any undrained water from freezing?

  10. walta100 | | #12

    Just to be sure you understand generally antifreeze is used to displace the water if you can’t open the tap and let the water out and the antifreeze in, I doubt you will get much if any antifreeze in and very little mixing with the water is likely to accrue.


  11. lekawa | | #13

    I can open shower/tub tap and washer dryer tap and hose bib tap. Tub is at opposite end of addition from hose bib. Still think little benefit?

    1. Expert Member
      NICK KEENAN | | #15

      Some thoughts based on my experience:

      A small amount of water trapped in a metal fitting can burst it if it freezes. Even the amount of water left in a shower valve or faucet when it is gravity drained can ruin it. I know of three ways to protect a valve: blow it out with compressed air, take it apart, or fill it with antifreeze.

      On the bottle of antifreeze it has a chart showing minimum protected temperature vs. concentration. The stuff I get at the hardware store protects down to -50F when undiluted. I don't dilute it, I figure if it encounters water left in the pipes it might get diluted. My experience is that propylene glycol offers protection beyond what it says in the chart, in a dilute solution it forms a slush before freezing and even if it freezes hard because it went through that slush stage it doesn't expand the way water does when it turns to ice.

      What I would do is fill the system with antifreeze. Do whatever you can to get antifreeze into every reach of the system, which means opening taps and letting it run a bit. That will get the antifreeze into the valves, which are the expensive components. Then turn off the pump and open the taps and leave them open, you don't want any opportunity for pressure to build. If there is a dead end that doesn't drain you might get antifreeze into it or you might not, and it might freeze and burst or it might not. But given what you've described I don't see what else you can do.

  12. walta100 | | #14

    I think you are making this your problem, I think you should make this the plumbers problem. Ask him if he needs make the place safe for freezing temp in a text message. He may think you are out of line where I live we likely at 3 weeks maybe 5 or 7 weeks before we will see will hard freeze.

    No good can come from you messing with his work, once you touch a pipe every difficulty he runs onto will somehow be related to what you did.

    The smart move is to hire trustworthy people that do good timely work and pay the bill.


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