Freezing pipes - domestic water service

[amorrison]

Winnipeg Canada has had a super cold winter (2013-2014) with frost depth now at 7-8 ft. The street domestic water supply pipes are being plugged with ice.
City workers are defrosting the pipes by electric (welder?) resistance heating which takes 20 min > hours? each time - there are 1000 houses to go !!!.

An idea - if the service water pipe has even a very small amount of flow - a contractor supplied separate pump (with its own cold water supply tank) could be connected to a kitchen hot water supply tap that would pump water INTO (reverse of normal flow)the hot water piping. This would push the hot water that is in the domestic how water tank into the street water supply piping and melt the ice in the pipe. Whalla !!

Comments please.

 

[weldstan]

Do the homes have backflow preventers? Isn't the problem, no flow?

 

[LittleInch]

If the flow is very small the hot water will become cold water very quickly in terms of distance from the house and not melt anything...

If contractor pumps goes a bit wrong, you blow up the hot water tank (assuming it is at main pressure) or start gushing water all over the overflow / relief valve outlet.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[maripali]

How it sounds? Connect hot and cold water pipes in to the closed circuit and with the additional pump do recirculation.

 

[moltenmetal]

Phase changes take a LOT of energy. Sensible heat (i.e. hot water) doesn't amount to much. Hence it takes a LOT of hot water to melt a little ice. Electrical resistance heating is putting in lots of heat right where it's needed.

Anywhere there's frost penetration of 7-8 ft, when the basement footings are probably no deeper than 6', has likely got problems which go well beyond some frozen pipes...

 

[cvg]

this is also a problem farther south in the states this winter.
the simplest and recommended method of keeping the lines clear is to leave a faucet running in the house to keep the water flowing. pumping water back through the service line into the main is not recommended due to possible cross contamination that the city is unable to verify or control unless there is a check valve which will prevent it. If the line is truly frozen solid then there will be no flow back through the service line anyway.

 

[MintJulep]

To reverse the flow you need to change the pressure gradient.

You will destroy every water heater in every house.

 

[Timelord]

In my city it would be against the law to backflow any water into the municipal system. There is now a building code requirement for a backflow preventer at the meter. I know this because recently, they replaced the grandfathered meters (mine included) with new ones with the backflow preventer. The new valve caused my hot water heater to leak at all the threaded joints. I had to add a small expansion tank for the thermal expansion in the water heater.
One successful method I have actually used to thaw metal underground pipes when I lived up north is to clamp a welder to each end of the pipe and let the current heat the pipe itself, just like the OP says his city is doing.

Timelord

 

[Compositepro]

It takes very little flow in a buried pipe to keep the pipe from freezing. While the ground at pipe depth may reach freezing the rate of heat flow, in or out, is low. So there really is not a better solution than to maintain some flow. Because of the low heat flow rate it will also take a very long time for a frozen pipe to thaw.

 

[JStephen]

Yes, backflowing in that manner is a major no-no, not sure if it's illegal in all places, but certainly inappropriate and would be illegal if they started routinely doing it.

 

[moltenmetal]

The idea is a non-starter for many reasons, the biggest of which is that it wouldn't work in a pipe which is blocked. No flow = no heat transfer from sensible heat. If the thought is to push out the ice plug with pressure, that's a disaster waiting to happen.

 

[77JQX]

Just in case this thread inspires people to hook an arc welder up to a frozen pipe, this technique has known issues, including the potential for starting fires and damaging electrical devices. Because the affected pipes may have electric continuity to neighboring structures, these problems might manifest themselves in adjacent structures.

 

[weldstan]

Used welding power supplies multiple times to thaw my frozen water line at my cabin. Finally caved in and spent the money to heat trace and insulate - no problems thereafter.