Temp in Well Pit ??????

leadfooterDecember 7, 2006

We are in MN and our well pit is about 5 ft below ground. We have lived here for 8 winters and never had a frozen pipe but we always had a Jet pump in the pit and we just got a submersible pump installed. I am wondering if that jet pump put off any heat or not and will we have to worry about the pipes now or should we be good since we always have been?? I hate to run a light for heat if I don't have to.


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A jet pump works by recirculating the water, adding volume to the flow. That is why it has two pipes at the connection. One feeds in and the other out. Moving water does not freeze. In this case, new heat is added in the circulation loop, somewhat by coincidence.

A submersible pump does not recirculate. It is feasible that water allowed to stand for a long period at freezing temperatures could freeze. You need to ask the installer whether the new arrangement is freeze prone, because the real answer depends on the specific circumstances of your installation.


    Bookmark   December 7, 2006 at 6:20PM
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Your posts have a zen-like quality :)

What you assert about jet pumps confuses me, are you saying in this arrangement, the pump runs constantly? They don't recirculate so much (the ones I'm familiar with, the pool-pump types) but work more on a centrifugal force principle do they not? Water is trapped in the 'blade' of the impeller and exists through the outlet/feed as that's the only place it can, and water's drawn in through at the front/centre...as I understand it. The oressure tank provides the flow to the house and the jet pump fills that....are you saying the pump runs constantly? Sounds wasteful. (but would freeze less easily)

Leadfooter, are you saying the well's only 5 feet deep, or is that just where the pump sits, and the well goes down below that? I'm not sure how that'd work in terms of freezing, 5 feet down's not much, but if there's a well below that, and the pump's submerged, then that *could* be below the frost line, and you might be ok if the pump house is well sealed against the weather and insulated....

If you insulate the pump house and the pipes well, you may reduce the need for heating, although just the other week my BIL's well froze, they got down to -30C and forgot to turn the heater on.....I suggested they just put the heater set to "on" and put a 110v thermostat in there, ie a baseboard-type one, and set it to turn on only when needed. That to me would be an elegant set-and-forget system, but they seem to prefer to have to remember to do such things (or be there to do them)

If keeping the water running is the solution, here's another idea. A solenoid and water outlet arrangement in the pump house, it could even be an irrigation system type one - connected to a programmable switching thermometer module (radio shack used to sell them) or even a conventional house thermostat (which will switch moderate amouts of 24v hence the watering system solenoid, which is 24v - you could use a relay to protect the thermostat - thermostat detects potential freezing temp, turns solenoid on - water drains back into well. Circulation is preserved....

    Bookmark   December 7, 2006 at 7:58PM
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Zen. Zen. Aw, man. I havenÂt heard that since I was a kid, tryin to figure out if John Lennon was a visionary or a pot-head. I had to Google that. It turns out, it means something like: the difference between thinking and taking stuff for granite. (Ok, copper is big today. But granite is the next big must-have. Stock-up on it like toilet paper.) DOOD.

No, Peanuts. I am not saying the pump runs all the time. I am saying that the one that ran 8 years without freezing may have been saved by the fact that water circulates in a well-balanced system; and the movement carries new heat to the water that may be exposed to freezing temperatures.

The reason a jet pump is useful is that it causes what otherwise can be called a Âsnowball effect. (For those who live in Rio Linde, a snow ball is a ball of snow. When rolled in more snow, it gets bigger. You do understand Âgets bigger, donÂt you?)

Now, all that means that a jet pump creates a Venturi Effect, which draws water from the well and adds it to the circulating flow. The excess is the water available that is used in the supply system.

In any case, the water recirculates whenever the pump pumps. That is controlled by the accumulator tank. Since water is warmer than ice, even cold water from the well has heat to contribute to the recirculated volume. As long as this occurs timely, the water will not freeze. On average, it could be said to be continuously recirculating. More accurately, it does so occasionally.

But a submerged pump either sends water to the storage tank, or not. If a great deal of time passes and there is no addition of heat, the heat losses will cause freezing.

There is nothing particularly religious about this  Âthough I am honored. What you read is about the most basic, 9th grade education in the schools of the Â60s. With inflation, that would be post-graduate mechanical engineering today.

After all, we have to teach the kids how babies are made before we can expect them to make cars that run on rubber tyres. So please understand that we have to move the High School curriculum to college. That makes a mainstream Â60s graduate look like a guru, a word that almost translates to Chan, which in Japanese is: "Zen."

IÂm glad you mentioned this, pajamas. We donÂt have enough words that start with Z. And how the heck are we supposed to teach the babies that X is for Xylophone, when they grow up on Ipods?

Huh? Huh?


    Bookmark   December 7, 2006 at 9:32PM
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More about the pit. The pit is all concrete block with a concrete top. It has 2 layers of 2 inch insulation on top of it 4 inches total. The pressure tank is on the floor of the pit the new submersible pump is 80 ft underground.
I was thinking maybe the motor from the jet pump maybe put off some heat into the air and possibly warmed the pit some.
Apart from the heat in the air...To me when the pump needs to pump fresh water would be no different now than when the jet pump was on. As both add new water to the system and pressure tank when its needed right sothat would be exctly the same right???
I could put a cup of water on the floor and watch it to see it if freezes? But I am beginning to think nothing should be different than it was the last 8 winters.

    Bookmark   December 8, 2006 at 12:07AM
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All right, Speed Racer,
No one spoke to that yet. There is a certain amount of heat lost in the efficiency of a motor, but while this works to the benefit of your interest, it would never be an associated fail-safe mechanism.

The submersible pump is in the well so it imparts a little heat to that relatively small amount of water (compared to the aquifer.) By the time the water reaches the tank, you would have to call the heat negligible. It is the heat that exists in the well that delivers water as a fluid and so the tank is storing that, too.

In a two-pipe system, one is larger than the other, to accommodate the increase in volume. That also creates a differential in the exposure of the cold air to the water in the pipes, the larger one giving off more heat than the smaller because of the Âskin being greater.

The differential in heat tends to equalize, so a natural flow circulates within the loop. And since the loop goes thru a warmer environment, it flows heat, somewhat similar to a bubbler in a boat well.

Even so, these influences are not near as helpful as others. The well pit is a safe environment for the tank. Heat exchange between the air in the pit and the atmosphere is very limited. With the foam insulation and the underground location, you should have a freeze safe condition.

That would be under normal use and normal outages.


    Bookmark   December 8, 2006 at 11:41AM
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80' is a long way down...stuff'd never freeze down there provided there's not a lot of cold from above...so you are pretty safe, but, like I said for a few dollars you could put in a thermostat and a heater or lamp or something, then you'd know you were REALLY covered. You probably need a light in there when you're doing maintenance anyway.

    Bookmark   December 8, 2006 at 2:44PM
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In the original post Leadfoot says this well pit is in Minnesotta and the bottom of the pit is about 5' below grade.

Personlly for Minnesota where the frost line may be 48" I would have preferred the bottom of the pit to be a couple feet deeper, but considering he has had no problems in 8 winters I guess the 5' has to this point proven sufficient to the need.

Some people are under the assumption that frost penetrates from the surface downward but such is not the case. The subsoil temperature of the earths surface(geothermal temperature) is approximately 50 to 55degF.

The laws of physics state that heat is a form of energy while cold is the absence of energy in the same manner that light is a form of energy and darkness is the absence of ligth.

During the winter months the air temperature drops below the geothermal temperature and the heat in the soil is radiated into the air. The heat in the surface soil radiates until the surface soil temperature is at equilibrium with the air temperature. The heat energy in the subsoil then radiates into the cooled surface soil until it reaches equilibrium and in this manner the temperature of the soil continues dropping until the depth is sufficient that the dirt can insulate the geothermal temperature from the surface air temperature. Thus in winter the surface soil temperature is always the coldest and the temperature very gradually increases below grade until it reaches a depth were the geothermal temperature is constant. The deepest depth at which the soil drops to the freezing point of water (32degF) is known as the frost depth. From the frost depth the subsoil temperature gradually increases with depth until it reaches the constant geothermal depth. (Approximately twice the frost depth).

With the bottom of the well pit below the frost line, even though the average soil temps may be only 38 to 40degF nonetheless it still radiates enough heat into the pit to prevent the pump and pressure tank from freezing.

As was mentioned in a previous post, when the pump is running it is bringing water up from deeper in the earth where the water temperature will be approximately 50-55degF. thus with each cycle of the pump additional heat energy is put into the pressure tank.

The rate of radiation loss through the lid of the pit is now retarded by the insulation layer. The rate of heat loss could be further reduced by installing foam insulation board on the pit walls from the top of the pit down to the frost depth, but do not install insulation below the frost line bacause even though the walls are cold below the frost line, they are still slightly above freezing and there is a small amount of heat energy beging radiated into the pit.

    Bookmark   December 8, 2006 at 9:11PM
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What kind of pump wont matter. Neither generates enough heat to make a difference. A friend of mine has his expansion tank buried outside for his summer home (frost line is 48" and its a 5 foot depth). The installer does them all that way to keep them out of the house and , just as important, there is no need to drain the tank when you leave in the winter.

The issue is whether you feel comfortable with the margin of error. Frostline at 48" means that under the nastiest long-term cold spell the ground only freezes to a depth of 48". Actually, there's probably a safety margin built into that number. Sometimes the "frostline depth" is from the building code and means a depth that guaranties that the footing will be "below" the actual frostline. With the insulation on the pit, I'd live with what you have.


    Bookmark   December 11, 2006 at 12:38PM
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So, " his expansion tank buried outside  The installer does them all that way to keep them out of the house and  there is no need to drain the tank when you leave in the winter." Well, I wouldnÂt do that to my worst enemy (even though I only have one.)

If this is legal, IÂd be very surprised. Unless those tanks are made for gasoline storage, they have no business underground. ItÂs bad enough when someone has an air valve that spits water and has to write in to ask why. Imaging digging that puppy out to check for a service problem.

I suppose it isnÂt all that bad in the summer  unless it rains every night.


    Bookmark   December 11, 2006 at 6:07PM
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It's legal, common, and a good idea. In fact, I did the same to mine when I built, although not for the same reason. I did it to mainly to save space in the house. As a benefit, when you run water from the tap, it comes out cold, instead of room temperature. The neighbors are jealous.

You seem to think that it's a direct burial expansion tank. Nope. Like the original poster, it's in a chamber. The tank is fiberglass, the fittings are either copper or stainless, and there's a simple strap on it to lift it out. Nothing to rust and easy service. An empty tank only weighs a few pounds and I've easily pulled mine out by myself when I was setting up the system.

If it leaks or spits water out the valve, it does so outside. No mess.

I don't recommend this method to my enemies, only my friends.

    Bookmark   December 13, 2006 at 6:23PM
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Are well pits legal to construct nowadays? If the pit fills with water, it could seep down and contaminate the well.

    Bookmark   December 14, 2006 at 5:50PM
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