Exterior pipe insulation
Hello
This is a general question that I’ve never been able to wrap, pardon the pun, my head around.
How does wrapping exterior (or non-conditioned areas) 1/2″ water pipe in insulation prevent freezing?
In my specific context I’m talking about zone 4C where we see some freezing days, but not extremely low temps. In non-conditioned areas and runs to garden hoses wrapping the 1/2″ pipe in foam insulation is supposed to prevent freezing but with the insulation being so thin surely the exterior temperature ‘reaches’ the pipework very quickly?
I can understand if the pipe in question is in frequent use bringing in new water that is above the freezing point, but if the tap, for example, isn’t used very often does the thin insulation really buffer the low exterior temperatures or is there another element at play? Especially when it can be difficult to fully insulate bends, taps, bibs etc in addition to just straight runs.
The context is that I’ve got some water pipes to run for an exterior shower and hot tub area for a client and I’d like to better understand the principles at play so I can install things properly to prevent freezing pipes.
In a similar vein, I’ve got an exterior water tank that on the outlet side has various 2″ valves and junctions. I’ve been told to build an insulated box over the area to prevent freezing from blowing the joints/valves. However I’m also having difficulty understanding how some thin insulation will prevent the exterior temperature from ‘reaching’ the inside of the insulated box. Perhaps this situation is relying on latent ground warmth to keep the inside of the box above freezing? In which case I should recess the box perimeter into the soil to ‘air seal’ it perhaps?
Thanks in advance for your patience on this naive question!
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Replies
Quinn,
Your question may be naive, but it seems you understand the issues better than those recommending the insulation. Insulation slows down heat flow. No more, no less. So, if an uninsulated pipe freezes in a certain time at a certain temperature, an insulated pipe will freeze more slowly. It will still freeze eventually, as the heat is lost through the insulation.
In a region where the temperature does not drop too far or stay below freezing for too long, a bit of insulation will "prevent" freezing by buying you some extra time. But we seem to see nearly every winter that a region which normally doesn't get that cold manages to get that cold for long enough and everybody's pipes start freezing. (Polar Vortex anyone?)
It is also useful to understand that water gives off much more heat as it freezes than it does when it is simply chilling. It takes about 4 J/g of heat to drop the temperature of water 1 degree C. But it takes 334 J/g to freeze a gram of water. So, in order to freeze the water in your pipes (or tank), you've got to move a LOT of heat out of the water. That skinny bit of insulation resists this heat transfer and buys you much more time than you might expect. Still, if you keep the temperature below freezing for long enough, the pipes will freeze.
For your water tank, making the insulated box air tight and connected to the soil will indeed provide extra protection against freezing, just as you expected.
You might also note that PEX pipe is relatively immune to freeze damage, and you might consider using it for these runs. PEX is "stretchy" enough that it generally won't split if the water in it freezes. The plastic is also less conductive than copper so it won't lose heat as quickly. PEX is, however, very prone to UV damage and must be completely covered in any exterior location. Covering it with insulation would be a great idea.
Or, just turn off the pipes and drain them in freezing weather like those of us in cold country do. How often is that outside shower going to be used when it's below freezing outside?
Hi Peter
Thanks for taking the time, I'm glad I asked it helps me understand the elements at play and avoid future issues!
A quick follow up if I may.
The water tank is 800 gallons, given the heat transfer that would occur trying to freeze this volume, is it therefore better to keep it full in winter rather than drain? We can and do drain the outfeed pipe and valves that will be covered by the above discussed insulation box. Thanks again