Plumbing, Heating and Pool Repair Guides

Unthaw Frozen Tub Drain


WeT HeaD KnowledgeHi my name is Charles Coleman and I am looking for a way that I can unthaw my tub drain and all of the drain pipes are unaccessible. So is there a chemical or something that I can put in my drain that will thaw the ice and it must go through standing water.

The Plumbers Response
(By Johnny)

I’m afraid there is no magic chemical that you can pour in the drain that will melt through ice. At least not one that will leave your house standing when the ice melts. Drain snakes are also ineffective on ice as it is a lot like a single ice skater trying to wear out the ice on a pond, it just ain’t gonna happen. On smaller supply lines plumbers have a thawing machine they can use but it is ineffective on larger drain lines. On drain lines a high pressure water jetter can be used and the water from the jet will quikly melt the ice however getting it to go through the trap under the tub could be a problem. I guess by now you are seeing there is no magic anything that can help. But, fear not there is. The magic tool is heat!

Many times people lower the heat to save money and it comes back to bite them in the form of frozen pipes. Turn up the heat to a higher level than you have been using. I’m not talking uncomfortably hot either but just a normal heating level that is not a conservation level. Open things up so the heat can get into unheated areas like cabinets and closets spare rooms etc. Now lets find where that pipe is frozen.

A drain pipe in good condition will normally drain dry after use and not freeze. However, there are conditions where a drain pipe can freeze. A clogged drain can freeze as it will hold water in the pipe, a drain that is not pitched properly can hold water in sags, or, bellies, that can freeze, and a dripping faucet can allow water to go down the drain at a low level that can cool off and freeze in the pipe. this is one of those things that make me cringe when I hear people offer the advice of leave a faucet dripping to keep the pipes from freezing. I have seen where a dripping toilet or, faucet has frozen the main sewer line leaving the house outside underground. That’s an expensive job for the jetter or, waiting until spring.

The only place your line should be able to freeze if you did not have any of the freezing conditions above is the trap under the tub drain. The trap in most cases is a shaped drain pipe that holds water in the which prevents sewer gases from coming into the home. It should be almost directly under the tub drain or within a short distance. Getting heat to the trap should solve your problem. Get access to this trap either through a wall from a room on the backside of the tub drain or through a ceiling below. Direct the flow from a hair dryer or heat gun into the space where the trap is and watch the magic. Be careful with heat guns as the temperature from them is hot enough to ignite some things. If this doesn’t work then you have to look for pipe defects like the sags I mentioned earlier but this should work in most cases.

After getting the drain flowing again you have to look at why it froze. Is there a cold draft going though the joist area? Is it over an area where the heat was turned off or unheated? What can prevent it from happening again? Repy back and I may have some suggestions for you.


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