Frozen Pipe Prevention

[stuhrw]

Hi. I recently moved up to Alaska and purchased a home, my first. I'm looking at the hot water heater and notice a little mixer valve at the outlet, which appears to mix a small amount of hot water to the cold water line?? Is this a local thing to prevent frozen pipes or am I looking at something else?? We didn't have any problems last winter, but I want to be extra-cautious this year as we've already seen -5. Do I need to let my faucets drip or does anyone know if there are devices like the one I'm talking about that actually prevent pipes from freezing? (other than the plug in wrap around types that you see in home repair stores). Thanks!

[LazyPup]

Extremely cold climates present some rather unique challenges to plumbing and having never been to Alaska, I don't feel myself qualified to give an absolute answer to your question, however based upon my knowledge of plumbing, and more specifically plumbing in the colder regions of the lower 48 plus my knowledge of the physics of water I would say your conclusion about that valve is remotely possible, but rather doubtful.

It is far more likely that the valve you are looking at is a whole house tempering valve.

The Plumbing codes mandate that the domestic water supply may not be operated at temperatures in excess of 140degF and to prevent scalding showers may not be supplied with water greater than 125degF.

The quick, easy, and least expensive method to meet the code specifications is to set the water heater to a maximum of 125degF however, when the water heater is run at this temperature we end up using almost pure hot water in the shower which results in a very high demand rate on the water heater. As we increase the demand from the heater, that in turn increases the rate of cold make up water entering the heater. Keep in mind that the more cold water we feed into the water heater the greater the rate of dilution in the water heater, which rapidly drops the temperature of our hot water reserve in the heater tank.

A very good solution to the problem is to install a "Whole House Tempering Valve" on the output of the water heater. We can then turn the temperature of the water heater up to 175 or 180 and as the water leaves the tank, passing through the tempering valve the hotter water is blended with a bit of cold water to reduce the temperature to the mandated 125degF.In most cases this will have the end effect of nearly doubling the capacity of the heater in its ability to supply hot water to the showers.

Now in regards to how to prevent freezing. Anyone who has lived in an extreme cold climate for any length of time knows that you can reduce the risk of pipes freezing by leaving a faucett run slightly to maintain motion in the water. As a result of this most people believe that water will not freeze while in motion, but that is not true. Water will freeze when it reaches 32degF regardless of whether it is in motion or not, which is evidenced by flowing rivers freezing over in winter or the snow making guns they use on ski slopes.

When we leave a faucett running we are actually taking advantage of geothermal heat. The Plumbing codes require that we must bury the incoming water supply lines at least 6" below the average frost depth for any specific region. The mean average temperature of the earths crust for the first 100 to 200 foot of depth is 55degF however soil is a relatively poor insulator and as surface air temperatures drop the surface soil temperature drops proportionally. The mean average depth to which the soil temps will drop to 32degF is called the "Frost depth". From frost depth to a point about 25% deeper than frost depth the soil temperatures gradually increase from the 32DegF freezing point to the natural soil temperature of 55degF. As water passes through the underground pipes heat will be transferred either from the water into the soil or vice versa. (Heat is a form of energy, while cold is the absense of energy, therefore the direction of heat flow is always from the hot side to the cold side.)

If all the faucetts in a house are turned off and their is no flow, the water in the pipe remains static and if the air outside the pipe is colder than the water in the pipe the latent heat in the water is radiated out through the pipe wall until the water temperature drops to the air temperature. Once both the air temp and water temp are at equilibrium there is no more transfer of heat.

Water has a rather unique characteristic in that it does not reach maximum density at freezing as does most other substances. Water reaches maximum density at 39.6degF. If water is then cooled below that temperature it rapidly expands until it forms ice. Ice is approximately 9% greater by volume than what water is at 39.6degF. Since water is a non-compressible substance as it expands that 9% inside a sealed pipe it will rupture the pipe wall. Leaving a faucett open slightly now has a twofold effect. 1. By continually allowing some water to exit the piping system it compensates for the increase in volume and 2. the incoming cold water is continualy warmed by geothermal heat from the soil surrounding the pipe, thus the water temperature remains at approximately 35 to 55degF which keeps the pipe slightly above the freezing mark at 32degF.

Anyone who has lived in a cold climate for an extended period of time and fought the problem of frozen water pipes knows only too well that the pipes in the core of the house do not freeze. The freezing occurs in unheated crawlspaces, basements, attics or where pipes run through or very close to outside walls.

One of the first considerations when designing a home for cold climates is to try to locate water demands in such a manner that you do not have pipes running in outside walls. When pipes are run between joists in a basement or crawspace the key is to insulate the pipe on the underside to prevent cold air from drafting in, but leave the upper side of the joist bay open to allow some residual heat to migrate through the floor in that area keeping the pipe above freezing. The same is true if a pipe is in the wall. Insulate between the pipe and the outside wall, but leave the space between the pipe and the inside wall open to permit a slight amount of heat to migrate through the wall keeping the cavity above freezing.

In an extremely cold climate area it might be adviseable to install a return loop on the cold water system in the same manner as we sometimes do for instant on hot water, then install a small circulator pump to keep the water in the cold lines in motion. This would continually circulate the cold water through the warmer core of the house, which would keep the water at an even temperature and prevent the cold spots in outside walls from getting cold enough to freeze.

Keep in mind that when their is no flow the water in the hot water lines can cool enough to freeze as well, therefore you would want a circulator on both the hot and cold water lines, but then, no one will complain about instant on hot water at the shower either.

To get a more finite anwer I would suggest you talk with some of the old gray haired plumbers in your region. The can no doubt offer you some other suggestions that would be of value.

[xroad]

Freeze protection valve

I remember seeing in TOH magazine ... a valve you put under the sink at the water supply lines ... If the temperature dips to a certain point, the valve will start to leak. The moving wtare will draw warmer water to replace the cold water and reduce the chance of a frozen pipe.

Now I cannot find info on that valve. Any help out there?

-xroad