Amount of water in a shower trap?

Old 01-04-18, 07:49 AM
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Amount of water in a shower trap?

We have a shower trap that is (brilliantly) located in an unheated craw space. During our first winter in the house, the water in the trap froze. We have added insulation around the trap ( not a big help, but it can't hurt!), but as temps. get down towell below freezing levels, I add about a cup of antifreeze. So far, so good, no more freeze ups.
My question regards the volume of water normally in the trap, and how much antifreeze should I add to keep things flowing, especially since we are getting predictions of "record low temperatures".

As always, thanks in advance.
Old 01-04-18, 08:11 AM
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Actually the insulation might hurt if it blocks off the heat source . Insulate on the cold side leaving it exposed to the potential warm side if possible.

The antifreeze is a good idea. 8 oz would probably be sufficient to give you a 50:50 mix.
Old 01-04-18, 08:16 AM
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The trap for my water heater drain is in a spot prone to freeze so I pour some RV anti freeze in it every winter and never had any issues. Which reminds me, I forgot this year guess I better go do that now!
Old 01-04-18, 02:31 PM
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A two-inch trap (standard for a shower) MIGHT hold as much as 12 ounces but I think a half-cup (4 ounces) of antifreeze should be sufficient to well below zero.
Old 01-05-18, 08:40 AM
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Thanks again for the helpful info.
Xsleeper, the crawlspace does not have a heat source.
Old 01-05-18, 09:06 AM
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Here's a visual on how much water the trap holds, it's called depth of seal:
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