hi i had a hot water heater that would only last about 10 minutes on pure hot. it was in our house when we moved in. so i replaced it with a whirlpool 30 gallon hot water heater that has the cold water in at the bottom and hot out at the top. it showed to wire 220 so i ran new wire and its own breaker for it and now it seems we have the same problem bumped up to about fifteen min now tho. i still dont have very long hot water and the hot is usally the only thing on. the hot water heater is located only about ten feet from the tub so i dont see how i could be losing hot water on the way and all the lines are new also 3/4 in hot water lines any one have any ideas as to why i do not have much hot water.
This sounds like a mobile home heater. 30 gal is not enough to service more than one person with short showers. 40 gal would be min recommended for two people, but for electric, make that 50 gal. Electric heaters are slow to recover.
With an avg GPM of about 3 GPM, you'll exhaust the 30 gallon tank in 10 minutes. If your shower head is rated at 2GPM, then you'll get about 15 minutes.
As was previously stated, recovery time is much slower on electric WH. This is why one typically puts in larger electric units to ensure ample supply.
Your other option, is to increase the temp up from 120 to maybe 125. Then as you are showering, you'll mix more cold water in with the hot water to get longer run time. If you have kids, this is NOT recommended due to the potential for them to be scalded.