Suggestions to stop sump pump PVC discharge pipe from freezing

[ironmanvsaquaman]

I need to prevent freezing of a discharge pipe for a sump pump. The pipe is 1.5-inch PVC. The section that's prone to freezing has a gradual downhill slope.

I was thinking of using a heating cable such as this:
https://www.menards.com/main/plumbi...heating-cable/hc6a/p-1444444946552-c-8588.htm
But the manufacturer indicates that it should only be used on "water-filled" pipe. Is there really a danger if these heaters are used with drainage pipe? I wouldn't expect them to get hot enough to melt PVC, since the heating element is covered in plastic insulation.

Is this another case of instructions being written to satisfy lawyers rather than in accordance with practical reality?

If it really is a bad idea to use a heater like this, what other options do I have?

Thanks!

 

[Reach4]

Where is the line discharging to -- can that accept water at a high-enough rate?

If you can keep the part of the line in non-heated space going downhill, and the discharge area is open, then I expect the line to drain. No bellys in the path.

An air admittance valve or vacuum breaker at the peak altitude for the pipe might let the pipe empty quicker.

I am also wondering about using the same float switch to provide power to the heating cable that provides power to the pump. If the pipe is somehow already frozen enough to block flow, then the pump could deadhead. Using a hole larger than the common 3/16 drill in the anti-air-lock hole , squirting water toward the pump, could provide enough turbulence around the motor to improve cooling. Just an idea. I expect a 1/2 hp or smaller pump would be bothered less by deadheading. I would expect a cast iron pump to not have a problem where plastic would.

 

[Sponsor]

 

[ironmanvsaquaman]

Thanks for the reply, and apologies for the long delay. Had a bad bout with some flu-or-covid-like bug which sidetracked me.

Where is the line discharging to -- can that accept water at a high-enough rate?

If you can keep the part of the line in non-heated space going downhill, and the discharge area is open, then I expect the line to drain. No bellys in the path.

The line comes out the side of the building and continues to the edge of a gravel drive where it discharges into a trench running across the drive then just runs downhill on the other side of the drive. No issues with water backing up once it's discharged.

I am also wondering about using the same float switch to provide power to the heating cable that provides power to the pump.

I like this idea. Sounds like a good way to avoid burning a bunch of money on electricity. I think I'd probably need to rig it up with a timer as well to keep the heaters on for a few minutes after the pump shuts off.

Here are the basic specs & dimensions of the sump system:

PUMP:
Barracuda (Menards)
model BA92751
SKU 691-3210
cast iron base
stainless motor housing
3/4 HP
80 gal/min

VERTICAL LINE:
Approx 16.5’ of head (with pump sitting on basement floor)
Vertical section is 1.25” flex pipe in heated space
Based on the performance chart it should pump slightly less than 60 GPM. The actual flow may be lower still, due to restriction from the 1.25” diameter flex pipe. The literature does not specify the diameter of pipe for which the flow rates in the chart are achieved.
The basement doesn't have a sump pit, but it will be getting one in the future. When it does, the head will increase by a few more feet.

HORIZONTAL LINE:
Discharge pipe is 1.5” PVC
Approx 45’ interior run in unheated space (1st floor) @ approx 0.72”/foot slope
Approx 29’ exterior run. Slope is slightly steeper than interior run.

After the line froze and I got it thawed out, I did adjust the slope of the exterior run. It originally had a steeper slope where it came out the wall and had a bow to it so that the slope gradually became more and more shallow with distance from the building. No part of it was ever horizontal or uphill, but perhaps it was shallow enough to let ice build up over time. I rearranged the supports for this exterior run, so that the slope is now very uniform. (It'd be nice if this was the cause of the blockage and my adjustment will negate the need for any heat.)

 

[LLigetfa]

My 1.25" poly sump line is buried with 2" rigid insulation sheet on top of it. At the end of horizontal run it turns vertical and is insulated with 4" rigid pipe insulation up to the surface. From there it curves in an arc into the open end of a 4" ABS elbow that then turns back down underground to join up with 4" big-O corrugated pipe that slopes down toward a drainage ditch where it breaks to the surface. I keep a lot of snow cover over the pipe and over the drainage ditch.

I don't use a check valve so the 1.25" poly pipe drains back into the sump pit. I adjusted the float switch to allow for the volume of water that drains back. The transition from the poly pipe to the ABS elbow is air gapped so the poly line can drain back and the big-O pipe can drain to the ditch. If the big-O were to freeze, then the water will spill out the top of the ABS elbow and run on the surface down to the drainage ditch.

My iron filter and water softener backwash into the sump pit so there is a frequent supply of water to keep the line warm enough not to freeze. I have a high water alarm on my sump pit JIC. This has worked well for me since 1998.

I have other underground 4" pipe to drain my eavestroughs and those I heat with roof deicing cable. I periodically turn on the heat when it gets warm enough for the ice in my eavestroughs to melt and when the electricity rates are low. Those too have worked well since 1998 except for one time when a rodent chewed the wire.

 

[ironmanvsaquaman]

Here's how I'm planning to use an AAV:

Is there anything wrong with this arrangement?

I have other underground 4" pipe to drain my eavestroughs and those I heat with roof deicing cable.

I really like the idea of using roof deicing cable. How hot does the stuff get? Is there any risk of the PVC pipe softening/melting if I have the cable strapped up against it?

 

[LLigetfa]

How hot does the stuff get? Is there any risk of the PVC pipe softening/melting if I have the cable strapped up against it?

Is is not too hot to touch so I doubt there is any risk of it melting PVC so long as it is not coiled up.