Blowing out water pipes

by Phillip

I am planning to buy a compressor to blow out water pipes for winter. The pipe is 3/4 inch and approximately 50 feet long.

What size compressor would I need?



Hello Phillip:

Yes, it's getting to be the time of the year in the Northern Hemisphere where we have to be concerned about water freezing in pipes that are exposed to the frigid wintertime conditions.

What you need to blow out a fairly small water pipe as you've outlined above is a small compressor.

Let me ask you, are you just going to use the compressor for this? If so, then perhaps you might rent an air pig or small air tank, fill it up with compressed air at the local gas station, and use that to blow the lines instead of buying an air compressor.

On the other hand, once you've got an air compressor, you'll find lots of uses for it.

In order for the water line to be voided of water, you need to fill it with compressed air fairly quickly. The compressed air, flowing into the water pipe, will drive the water before it and out the other end.

If the water pipe is metal, you can use compressed air at industrial pressures...perhaps 120 PSI or so. If it's not, make sure that the pressure you use doesn't exceed the burst pressure of the pipe, or you might be creating more problem than you wish.

If my math is correct (and yes, you do want to check it) a 3/4" pipe x 50' will hold about .2 cubic feet of air. If you introduce a few cubic feet of compressed air at, say, 30 PSI, you'll have plenty to drive the air out of the pipe, as long as the outlet is below the air inlet.

If there's convoluted piping, add higher pressure (maybe 50 PSI if the pipe can stand it) and get the flow of compressed air going into the pipe as fast as you can to build the volume of air inside the pipe quickly, to drive the water out before it.

It will help if the outlet from the pipe is as large a possible to allow the water to get out more easily. Open the drain tap fully.

When all that's coming out of the outlet at the end of the process is a little mist or just air, you're done.

So, a small compressor that has a tank that holds 2-3 cubic feet of air, one with a regulator to reduce the outflow pressure if need, and an air hose with a high flow blow gun is what you'll need.

Hope this helps,


Comments for Blowing out water pipes

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Nov 05, 2018
Re: post of Nov 3 - Puzzled
by: Bill

Howdy... what part of the information you have asked for is not already on the page about blowing out sprinklers on this site?

Nov 03, 2018
Winterizing ingroud pool in Ottawa with Air Compressor
by: Anonymous

Hi Bill,
I would like to use my 10 Gallon Air Compressor to blow the lines.

What pressure should I use?
What kind of couplers/fitting do I need to buy for 1/4" air compressor air pipe?

Thanks for the response


Jul 13, 2018
Winterizing - for Ellen
by: Bill

I am not a sprinkler person, yet when winterizing mine, it essentially means getting all the water out so that when the lines freeze water inside doesn't freeze too and split the lines, since water expands as it freezes.

So, no reason you can't do it yourself, and the how to is covered in the comments on this page and on the page itself.

Good luck.

Jul 13, 2018
Winterizing - for Ellen
by: Bill

I am not a sprinkler person, yet when winterizing mine, it essentially means getting all the water out so that when the lines freeze water inside doesn't freeze too and split the lines, since water expands as it freezes.

So, no reason you can't do it yourself, and the how to is covered in the comments on this page and on the page itself.

Good luck.

Jul 13, 2018
My sprinkler system winterizing
by: Ellen

I have a very small sprinkler system and lost my lawn guy that always took care of winterizing. Can I do this myself and how?

Oct 24, 2017
Plumbing blow out fitting
by: Anonymous

Amazon has plumbing blow out for just that they are 11 bucks ...compressor to faucet fitting....done

Jan 31, 2017
Back Flow Preventer
by: Bill

A back flow preventer is essentially a check valve, or as it's also known, a one way valve.

That being the case, if you blow compressed air into a pipe that has a back flow preventer, that device will likely stop the air passage at that point.

Jan 30, 2017
Outside Facet with Back Flow Preventer
by: Anonymous

What if your outside facets have back flow preventers? Will the air compressor work?

Nov 10, 2016
Water leaking after I blow out line
by: Anonymous

I have blown out my outside line, leave the faucets open and the water shut off. A day or two later I noticed the faucet dripping.. Why is that happening if the water is shut off?

Nov 13, 2011
PVC pipes
by: Rick

You suggest 120 max PSI for metal pipes. My cabin has PVC pipes. How much pressure for blowing out PVC lines for an 800 sq ft. cabin. Maximum pipe length is probably 25-20 feet.


I don't recommend any pressure for PVC as I would be concerned the pipes would burst. If you must, try it at 10 PSI. It's the volume that will do the job, not necessarily the pressure.

Sep 14, 2011
Can I blowout a 2" sewer line
by: Russ

In my work shop I have a 2? sch 40 PCV sewage pipe that runs from the sewage pump (in the shop) to the septic tank. The line is about 150? long with about a 5? rise to the tank. Can I blow most of the water out of this line with a 2hp 130 psi shop air compressor?



Very doubtful Russ. You don't need high pressure, you need a high volume of air, and a 2 HP will not deliver enough, as far as I'm concerned. The other issue is a sched 40 pipe won't withstand much pressure, and if there is a weak spot in the pipe wall, or part of the pipe wall is unsupported, and there is a, ummmm, blockage in the line, then you could blow out the wall if you put too much pressure into it.

Apr 12, 2011
cabin winterization
by: Peder

I need to blow out my cabin water pipes in the fall to prevent them freezing in WI in the winter. I assumed I could buy an adaptor to go from my air compressure connection/hose to my garden hose faucet connection but one does not exist that I can find. So I am so far stuck with using an RV tire filer connection which loses a lot of the pressure. Does anyone know of a connector that allows for a connection from an air compressor hose to a garden hose faucet?


I know of none off the shelf. However, if you can attach a coupler to the water faucet, and a connector to the end of the air line, you have solved the problem.

I don't know the thread of the faucet. Visit your plumbing store and tell them you want to add a fitting to the faucet that converts to a copper sweat on other side. From that you can easily add what's necessary to install you coupler.

See Couplers & Connectors for more info and do read the post preceding this one, too.



Oct 27, 2010
home water pipe blowjob
by: ex-property preservation dude

Done this just too many times.... get an old garden hose (1/2"-5/8" max) just fit hose over a air nipple, one made to fit into the a bare cut air hose works fine, but I have used the treaded type also, (spare, from your compressor), cut the garden hose any length that u wish, but u are going to want the end that screws onto the house hose spigot.
Make some to give away....

Insert the air hose nipple into the cut end of the hose w/ the nipple facing out, attach w/a proper size hose clamp (too cheap).

I use the washing machine hose bib's as we blew out the cold
lines 1st, then the hot lines, then w/ the water heater isolated & draining out the house (door or window whatever was closest) w/ a separate garden hose (not cut).

If no washer bibs just hose end to any water hose outlet, open valve all way,

Then open all faucets in house, sinks, showers, tubs, other hose outlets,..... turn off all water valves to toilets.... (no use blowing out your ball-cock).

If not on already, turn on air compressor, let run till cuts off.

Attach the compressor air hose to u'r new $2 air hose/water line adapter.

I do not like to use more than 50-60 psi, not necessary anyway.
let it blow until all lines are dry, can shut down faucets as they blow clear if you need to, I never had to.

Almost any compressor w/ a small tank will work, just not a 12v from your car....

U/r welcome.

Oct 18, 2010
Thanks bill!
by: Anonymous

Hey Bill thanks for commenting on my letter about using too much air pressure when blowing out my returns lines. I did have a pool company come out and pressure tests the lines, and they held the pressure fine. So therefore, I assume no leaks are in the lines and I didnt blow them up! LOL They also told me the same thing you did, that if the pressure got that high, more than likely it would have blown my rag out of the hole first! Thanks again!



Oct 17, 2010
This is great info!
by: TC

However I am trying this for the first time and I was missing a few details in the instructions. Where do you attach the compressor? To each faucet in the house from the top down? outdoor faucets? To each one in turn? We had a guy install two faucets in the lower garage one for hot and one for this where the expelled water will come out?
Any further instruction will save me for hiring times being how they are!!!
Than you

Oct 11, 2010
blew out return lines with air compressor on highest setting
by: Anonymous

I blew out my return lines in my inground pool today.. i just found out that you shouldnt use too much pressure or you could blow out the joints in the lines. Now I'm worried sick because I had the compressor set on its highest output. The pool lines are all new this year. there are for jets and i capped three of them at first then started the compressor from main opening by the filter and held a wet rag around the opening to seal around the air compressor nozzle. after the bubbles started coming out of the open jet, I capped it then proceded to the next jet ...taking off cap and letting the air bubbles come out then recapping it again. I did this over and over until I had done all the jets. Do you think I could have hurt the piping or joints.. please respond. Now Im very wrried that i might have hurt them. Thank you .. I used a craftsman compressor from Sears.


While it is possible that you have damaged the lines, I personally think it unlikely.

Your water lines have a burst pressure rating that would, I expect, have allowed the air pressure build up to that burst point to first push your wet rag out of the way, and let the air pressure out there. Compressed air always flows to the point of least resistance.

Also, if your lines are buried in earth or cement, the pressure exerted on them by the earth or cement around them would have helped prevent a line blow out.

Unfortunately, you will have to call in a pool professional to test the lines to be sure.



Jul 15, 2010
by: John

Rick D, I had the same question. Sure enough, here is one adapter:

Apr 21, 2010
Adapters and Attachments hard to get
by: Rick D.

I have a well. I use the compressor to blow out the line.

I attach it to the spigot at the ends of the lines with the well at the opposite end.

I had to buy 2 , or 3 parts from the local hardware plumbing store - it order to put together an attachment adapter so as to be able to interconnect the air compressor hose to the garden hose spigot.

I can't believe that with people all over the place using air compressors to blow out thier lines that they don't have an all in one interconnect adapter that you can get for it.

If anyone finds it please let me know where to get it. I'd like a spare.


Jan 02, 2010
Reduced water pressure
by: Anonymous

I added a water line for my new frig to make ice cubes, but when was finished, the water presssure in the kitchen was reduced in half! Do I have "junk" building up in my water pipes? I have a compressor, but if I blow out the pipes, will it clean out the junk in my pipes? AND, how/where would I hook up the compressor to blow out the pipes? Please help an old grandpa figure this one out...

Howdy: I, too, have added a water line to a fridge from the water supply, and no way should that have reduced water pressure in the kitchen.

I expect you shut the water off in the area you were adding the new line, and my thought is that the valve you used to shut off the water isn't open all the way, and may be throttling water and lowering water pressure.

Could you have junk in your water lines? Maybe. No way I can tell. If you do, it will be a build up of scale likely, and I don't think trying to clear that with compressed air will bring any success.

When blowing out water lines, you need to add a fitting somewhere to which you can attach an air supply. You normally won't find one of these in a kitchen water supply, sorry.

Cheers & Good Luck.


Nov 24, 2009
using shopvac to blow out water from pipes
by: telecomtom

Hello Bill, how about the comment from Anonymous about using a shopvac to force out the water? the pipes were 1 1/4" diameter, which is larger than the water lines in my house (about 3/4" I think). There would have to be a battery or gasoline-powered generator to run the shopvac or compressor for however long it would take to get all the water out.

Another problem I might have is "dead ends." How to get the water out of the end of a pipe that is closed. For example, we were going to install a standard water heater (with tank) but opted for a tankless model instead. The pipe that was going to connect to the water heater is stubbed out, with an end that doesn't open. How does that work when the compressed air reaches that point? It seems like the water would just get stuck in the end and then would freeze when the house temperature drops below 32 F / 0 C.

These are interesting puzzles. But very real for some people like my humble self....

In order for the shop vac to work, you have to have air ingressing at the other end of the system. The vacuum pulls the water out...yes, but it can't pull the water if nothing is flowing in to replace it.

A power supply for a shop vac, as you point out, can be a problem. The same can be said for a compressor too, of course.

If the lines that are plugged are oriented downwards, and water cannot flow out as the rest of the lines are voided, then yes, you may have a problem.

Even using compressed air may not solve that one.

It seems to me that anyone installing a sprinkler should make sure that there is an access point at the end of all runs to allow the connection of an air line to blow the lines... but then, that costs more money, doesn't it.

Good luck.


Nov 23, 2009
Air Tank/ Air Compressor - blowing out lines
by: Tim

I am getting ready to try this for winterizing a small farmhouse in the mtns of North Carolina. I am not sure if an air tank or air compressor would
be better. Since this is the first time, I want to get it right. Any thoughts/ ideas????

Thanks, Tim
Hi Tim:

It's not hard to do, but you do need to know how much air you will require. A single, charged portable air tank, while providing lots of pressure, may not have enough volume to rid your lines.

Please see the details on this, and linked from, these pages about blowing out sprinkler lines.


Feb 02, 2009
Use a shop vac instead?
by: Anonymous

I blow out swimming pool lines (1 1/4 diameter 25 - 40 feet) with a small sized shop vac. You can run it continuously until the lines are bone dry.

Dec 28, 2008
by: telecomtom

Hello, I'm preparing for winter conditions, with air temperatures in the subzero range, that may involve loss of electric power and natural gas for several days. We have a Husky air compressor that we use for driving nailguns and small construction equipment like that.

Tom...too many subjects to answer here. Please see:



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