The Physics of Freezing and Freeze Protection

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Hello, I'm a new IG pool owner in NJ where we've been having below freezing temperatures at night AND daytime for a couple of weeks now with finally a break from freezing temps this week. Our pool is covered with a polycarb structure and we've been running the filter 24/7 during this time as well as heating the pool to 90F when we want to swim in it. The pool water gets down to the lowest of 65F in between heating/pool use. We also have freeze protect mode set at 34F.


In deciding whether we want to keep the pool open in future winters, we need information about when pipes freeze and burst to ascertain the risks we want to take in exchange for being able to swim in NJ winters.

More specifically, if our filtration system breaks or loses power:

1. First, is there any risk of below ground pipes freezing?

2. Is the risk more for the exposed pipes connecting to the equipment (vs underground pipes) that could be resolved if we build a shed over it or put foam around the exposed pipes, etc. ? I think the information referenced above about time to freeze refers to pipes located above ground, perhaps that at the equipment? My pipe is PVC and 2".

In deciding whether to keep our pool open for future winters in NJ, the main risk is should our filter stop running due to it breaking or losing power, will we have enough time to fix it before the pipes could freeze and burst. I know no one knows the exact answer of when this could happen b/c there are multiple variables as referenced above.


However, I'm just wondering if I have ENOUGH time to fix the motor BEFORE pipes burst. If the pipes could freeze in a matter of a few hours, then maybe we should close our pool during the NJ winter months of Dec-Feb. since we won't have time to repair before the damage occurs (like when it stops running in the middle of the night unbeknownst to us)

If it takes like 20-30 hours for the pipes to freeze, then I can keep our pool open during the long freezing temps of NJ winters and minimize our risk by buying an extra motor to have on hand and possibly putting our filter on backup on our whole house generator (don't know if I can yet depending on how much power it uses)

I appreciate any thoughts on this. Thanks.


Phuong in NJ



16" x 33' concrete wall vinyl liner IG pool, Jandy CL340 cartridge filter, Jandy 2.0 HP pump, Jandy JXi260 natural gas heater
 
1. Yes but it takes a lot longer for pipe to freeze underground vs above ground. You can prevent freezing all together underground if the pipe is buried deep enough to be below the frost line. However, the pipe going from above ground to underground is still vulnerable.

2. Yes and yes

Should power fail, the above ground plumbing will freeze first and the time to freeze is dependent on several variables. Draining the pad equipment can extend the time to freeze by quite a bit plus if there is air in the pipes for the ice to expand, even if the remaining water does freeze, it is unlikely to do any pipe damage. It is only when the ice expansion is constrained, that you can have pipe damage. So leaving all flow valves in an open position can also help.
 
Hi phuong. I can't answer your question but have certainly tried to figure this out for my own purposes ;)

I am running in Michigan (in an air dome) with similar concerns.
During the "deep freeze" before Xmas, my heater quit and I do not have a bypass. But since I keep my water in the 90-95 range and since my pump was still running, I was okay for the net four days it took to diagnose, ship the part and replace the heat exchanger (heater is indoors in a pool house.) In this scenario, my water temp did ultimately drop to high 70s over that time. The speed of drop slowed considerable as the temp lowered in the pool.

For the pump, I chose not to take any chances, so do have a single speed backup motor on hand in the event of failure and a shaft seal kit. I had upgraded to a vsp motor this summer while my existing pump was still functional with this in mind, and also "learned" how to change the motor so that I would know how under duress ;) to do this meant retrofitting a vsp motor instead of getting a whole new pump as I wanted the motors to be swappable in emergency.

For power outages, which I have had, I now run a 10k Generac gc (contractor style portable, not whole house, but good overhead) to the pool house and house. From the generator I was able to handily operate the pool pump, heater, chlorinator, house well pump, boiler pump and a few dedicated circuits for several days (and several gallons of gas ;)

Ymmv, but in my case I just decided that operating in winter was worth the precautions -- in my case I'm using the pool for a physiotherapy routine that helps keep me mobile despite arthritis in my knees and a replacement in my future. That meant having an electrician install an interlock kit to safely operate the generator, plus the cost of the generator. Our major, multi day outage was less than a month after this move, so it certainly felt like the right route ;)

Btw, I have enclosure envy ;) I'd love what you have but my footprint was a bit too irregular to make one of those work!
 
Is the risk more for the exposed pipes connecting to the equipment (vs underground pipes) that could be resolved if we build a shed over it or put foam around the exposed pipes, etc. ?
Click to expand...

Is your equipment pad outdoors? Or are you talking about pipes that run out and then into the ground?

My equipment is in a pool house, but the exposed pipes come out of the pool house for a few feet and then go underground. We built a box with thermax foam insulation inside and put a temp monitor in there. Since we keep the pool warm, the pipes and air inside the box also stays warm.

If your equipment is out of doors in particular, operating in winter may negatively affect your heater because the extremely cold intake air can cause condensation that is then highly corrosive as the condensate of combustion accumulates and soots your heat exchanger. If its possible to build a heated enclosure, this would protect your heater better, but note that you need at least an inch of makeup air venting for every btu...eg my 266k heater needs 266 square inches of intake venting for makeup air for proper combustion.
 
hey friends I know this is probably been answered but I have to ask anyway for piece of mind, 1 1/2 pvc plumbing only comes out of the ground at the filter pad (outdoor no protection) I have been running the pump anytime the temp drops below 32deg , temp tonight in east TN is gonna drop to a low of 28deg for just a few hours over night then warm up plenty over 32deg all day long sorry I'm advance and also ty all so very much
 
The table in the first post shows the freeze times for various pipe sizes and conditions. So if the temps are below zero for only a few hours, there is no chance of freezing in 1.5" pipe.
 
Just want to say, over and over again--every question I have ever had about pools is answered on this site. It is the greatest resource for pool care out there. We are selling our home and my summertime joy :)cry:). Our new home won't have a pool (yet). Getting ready to list our house and thought I would open up the pool for spring so that the new owner would know they weren't buying a swamp. Unfortunately, we will have a few days that may freeze in the next few weeks so we were worried about having it open and the plumbing freeze. This thread is exactly what I needed. Thanks to all for all the help over the years and hopefully it won't be too long that I have a pool again. Chris
 

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I've read through this thread and may have missed it, but would the level of salt in a salt water pool affect the temperature that the water will freeze? Say a level between 3000 and 4000 ppm?

Thanks.
 
rcy said:
I've read through this thread and may have missed it, but would the level of salt in a salt water pool affect the temperature that the water will freeze? Say a level between 3000 and 4000 ppm?

Thanks.
Click to expand...

Not really as much as you think. Significant freezing point depression usually requires a TDS much higher than 3000ppm. The question has been answered before-

freezing point of a SW pool
 
I appreciate the info on when pipes freeze, but what about the check/diverter valves? I have a 3-way combining two supply 1.5" PVC lines just before going into my pump, and another after the SWCG splitting the return into two 1.5" PVC return lines. Last night (actually, early this morning), it got down to 22° here. and although I covered (only loosely) my stuff with a tarp, I chickened out and ran the pump (a new 011018 Pentair variable speed, not updated in my signature) from 11p-8a at 1150 rpm (just in case), even though the pump's antifreeze mode (set to come on at its internal temp of 45°) had kicked in twice at 5:30p (30° outside) and 9:30p (28° outside). I did it because I became worried that the check valves would freeze.
 
The valve freeze rates should be about the same or a little longer than pipe as they hold about the same amount of water per unit of surface area. But at 22F, it would take a very long time for 1.5" pipe or valves to freeze solid (>30 hrs) so there is virtually no chance of freezing overnight.
 
Thanks, Mark. :) I didn't have a feel for how thick the walls of the valves are. I saw that your tables go down to 20°F; sometimes it gets down into the single digits here. Would it be advisable to go ahead and run the pump when the temp goes below 20°F? BTW, my lines come up out of the ground and go into the ground just before/after the valves.
 
It really depends on how far below and for how long.

But tarping the above ground equipment and pipes will help a little bit and allow you to go down a bit further than 20F. For 1.5" pipe with a tarp and a 15 mph wind speed, it would take more than 8 hours to freeze with a low of 15F (24F ave). Even at a low of 10F (21F ave) it takes over 6 hrs to freeze.

Add an incandescent light bulb under the tarp to keep air temps above 32F, and the pipes would never freeze.

One way to determine your risk is to use a proxy for the pipes. A small water bottle next to the equipment will freeze first so if that starts to show signs of freezing overnight, you know it is time to think about risk mitigation. Of course, if a cold snap is in the forecast, you have to be bit proactive.
 
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It will only prevent freezing while the pump is running AND for only those pipes that have water running through them. Lose power, no freeze protection.
 
Firstly- thanks very much to everyone who has contributed to this thread. Very helpful and very timely.

Secondly- apologies in advance for the "what about my specific situation?" nature of my next question. I have a small, 1500 gallon above ground pool (used to swim in place with help of a harness) with the default hoses (I'm still not sure if I'll move things around) that resides on my large screened in porch (ground level, concrete slab). I have a small electric heater and swg (intex) and plan to put up double layers of plastic around the porch so wind won't be an issue. I did a single layer of plastic last year and it certainly helped keep the heat of the pool in but I didn't feel like I got a lot of solar heat so I'm more focused on keeping heat in this time. Anyway... I'm in zone 7 so sub freezing nights are not uncommon and we will probably get a few below freezing days but it's not the norm for winter.

I'm not confident that the plastic will keep the porch warm all the time, and I don't want to constantly be checking the temperature and stressing over it. I'm not worried about the pool itself as it will be heated but just about the pump/filter/heater. If I'm reading this right, it seems like the combination of no wind, proximity to warm pool and the house (right beside brick wall of house), and maybe covered with a moving blanket would probably be enough except in the coldest of conditions, which is great because I'd rather not run the pump every night it's below freezing, it's really excessive for that sized pool.

My question is this: if it turns out I do need another heat source to keep the equipment from freezing, what might I use? I had thought perhaps an oil filled electric heater but all unobserved electric heaters make me nervous, especially around water. Someone mentioned a light bulb? I wouldn't want to heat the entire space and would be willing to build an insulated box if I could eliminate any fire danger.
Thanks for any input! I was planning on closing down the pool for the winter because I just didn't want to worry about making sure I was around to turn in the pump whenever it dropped below freezing but now I'm a little more optimistic.
 

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