I’ve been told to drip only the cold water line during a freeze.
This makes no sense to me since both lines at 3 AM are essentially the same temp.
I have a tankless system so there’s no heated water source warming the pipes.
Am I wrong about this?
yep, both sides.
regarding hot side lines not freezing. you get any distance away from a conventional water heater and, when the exposure to freezing temps is the same, the hot side is actually more likely to freeze than the cold side. seems i recall this to be due to less dissolved oxygen in the water on the hot side.
my proof of this is having thawed/ fixed a shit ton of frozen/ busted pipes over the years. i would say 80% of them were hot side lines.
This is a good question, actually; I’m not sure the old advice accounted for tankless heaters. Are you sure the hot water lines are the same temperature? I know how tankless heaters work, but
- Water retains heat really, really well, and
- If you’re just “measuring” it by putting your hand to it, I am not sure you really know.
That said, I don’t see the harm in dripping the hot water line if it’d make you feel more confident.
Hot water lines can absolutely freeze just as much as cold ones. I had a heating pipe freeze during our cold snap last week, which is much hotter water & a larger pipe than domestic hot water.
RickJay, I can assure you that the hot and cold water pipes will be at the same temperature the cold water pipe would be by the coldest hours of the night if the hot water tap isn’t dripped. While water does indeed have a large specific heat capacity, pipes provide a large surface area for losing heat to the surroundings and the mass of the water inside isn’t enough to keep that water warm either.
I say drip the warm. If the warm and cold water pipes are run next to each other, or at least in the same bay, the hot water pipe may help keep the cold from freezing by warming the air in the bay. Even if it’s only a degree or two.
I once lived in a place that had both cold and hot water pipes run outside … I dripped them both … there’s nothing intrinsic to water that was once 125ºF that stops it from freezing when it drops lower than 32ºF … I don’t know about this place I live now … we haven’t had freezing weather yet this season and now it’s already spring …
It depends on where the pipes freeze typically, but it doesn’t hurt to let both drip, except for slightly higher utility bill for the hot water. For me the place that needs freeze protection is in the crawl space where the pipe enters the house, before the hot and cold split off from each other, so I just run the cold. Inside the house there is heat, pipes run in good locations w/o cold spots, and if the heat goes out I get a alert.
My tankless water heater is on the exterior south wall of the garage. The water pipes run under the house in the crawl space, out through the foundation into and out of the water heater. Like all tankless systems, the heater only heats when I open a hot water faucet. I don’t circulate the hot water full time. And the heater doesn’t ignite unless the flow is high enough to trigger the electronic ignition.
This is what it looks like: Dropbox - File Deleted
The crawl space vents are open in this pic.
I have a light bulb on a freeze sensor to keep the lower cabinet warm when it gets cold.
Thanks again for the feedback. I thought I was doing it right.
Do you mind saying generally where you live? I didn’t know tankless heaters could go outside.
Tankless heaters generally don’t turn on unless the flow rate reaches some minimum threshold, so a dripping “hot” line isn’t going to be any hotter than a dripping “cold” one.
Not the OP, but I live in Southern California, and our tankless heater is on the exterior. It (almost?) never freezes here.