Plumbing – When to turn on backup water powered sump pump

Your best answer would be to try to eliminate the water before it gets in. Your best options will depend on the reliability of your electric source. A battery pump will only last so long. A watered powered pump will require a steady flow of municiple water. If you have a well it obviously won't work without power. The other consideration is how easily can you run a water supply line to the pump in your now finished basement. Water powered pumps are expensive to run interms of the cost of the water used and the amount pumped. The best models are close to a 1 to 1 ratio. The less expensive ones use 2 gals to pump 1 gal. In my area water and sewerage are combined in one bill. I would be paying a sewerage surcharge on the water the pump uses even though it would discharge in my yard. The water bill would still be less than your insurance deductable, and your rates won't increase due to a claim. I would use the electric as a primary pump and get a water powered unit as a back-up.

I fail to see a problem here. Increasing the discharge pipe diameter does not increase the load on the pump. Unless you have a pump manual that specifically forbids this (which seems very unlikely) relax and stop worrying about it - or worry about the battery running out, which is far more likely to be a problem in any extended power outage.

If you have such an unlikely manual, replace the pipe that offends you/it.