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In the event of water heater failure, I'm considering installing a water heater pan with drain pump per this answer. How can I determine the necessary pump rate?

According to the Insurance Institute for Business & Home Safety, for insurance claims, water heater failures make up 20 percent of all residential water loss incidents, and incur over $5,000 per claim.

From past experience with failed water heaters, it seems that the flow rate might be the full incoming flow rate? Either way, what is a conservative capacity? If I can't find an off the shelf condensate pump with sufficient power, I assume there's no reason I couldn't attach multiple pumps--plus I'd get the benefit of some redundancy, right?

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  • Failure, as in relief valve activation? That's going to take quite a pan to contain.
    – isherwood
    Apr 12, 2016 at 15:29

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It depends on what type of failure are you talking about. The rate at which water flows from a leak, is going to depend on the size of the leak. It could range anywhere from less than 1 ml per day, to the full supply flow rate.

If it's a catastrophic failure, you could be talking about the full contents spilling out in a matter of seconds/minutes, followed by the full supply flow.

In the case of a T&P discharge, it could be a tablespoon to a few cups. If the T&P fails fully open (not very likely), it would be close to the full supply flow rate.

If you want to plan for nearly worst case, you'll want a pump that matches the supply flow rate. In the event of a catastrophic failure, there's not much you can do about the initial surge. But if the pump can match the supply, you'll reduce further flooding until the supply can be shut off.

I don't have solid data on it, but I'd guess that serious failures are rare, and catastrophic failures are even more rare. Therefore, matching the supply flow could be a waste of money (unless of course the tank actually fails).

An automatic leak detection shutoff valve, is another way to reduce damage caused by a water heater failure. Though it won't do anything to prevent the water that's already in the tank, from leaking/gushing out.

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  • I've had two of my own water heaters fail catastrophically, both right at about the ten-year mark. After we finish our floors, I'd like to ensure that a water heater failure doesn't ruin them. Is it even feasible to match the incoming flow rate? How would I go about measuring it? measure from the laundry basin hot water faucet?
    – glenviewjeff
    Apr 12, 2016 at 17:19
  • I'm thinking I may be better off with an automatic supply shutoff switch--though if the tank corrodes and empties, which I believe is what happened previously, I'd want a pan and pump to try to prevent that from getting under the flooring as well. Clearly if it were a massive burst of water, there's no way to pump 40 gallons in a few seconds. I'm just not sure what, if anything, makes sense to do to mitigate these scenarios.
    – glenviewjeff
    Apr 12, 2016 at 17:19
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    Proper water heater maintenance is the best way to mitigate the risk of catastrophic failure. There's a sacrificial anode rod in the tank, which is designed to corrode instead of the tank lining. Inspection and replacement of this rod can reduce the risks of internal corrosion. If the corrosion in starting on the exterior of the tank, periodic inspection of the tank will allow you to replace the tank before a failure. Follow the manufacturer's maintenance schedule, and you should be able to avoid catastrophic failures.
    – Tester101
    Apr 12, 2016 at 17:36
  • Yes, I think this may be the key. I've never historically had the rod inspected, even though our plumber would inspect our sumps and flood control annually. Not sure why they never offered this.
    – glenviewjeff
    Apr 12, 2016 at 17:46
  • Also, from looking around, it looks like after about 9 years is when most of the failures occur. I'll also plan to replace my water heater proactively at 9 years. I may even consider switching to tankless at that point.
    – glenviewjeff
    Apr 12, 2016 at 17:47

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