Is it electric? have you checked to make sure the circuit breakers are both on? (Assuming 2 breakers for a 220 circuit). If all looks good, I'd call the installer for help.

Is it electric or gas? What temperature is the heater set to? A 50 gallon tank is plenty for a family of 6. Why did you change the old heater if nothing was wrong with it?

Good advice already.

Check out the specs for your new heater. If you don't have the literature, you can research it online. There should be a published First Hour rating, as well as a published recovery cycle time.

The first hour number is easiest to find as it's usually located on the yellow energy guide sticker applied to the tank. In the upper left hand corner. It'll tell you how many gallons of hot water you can expect to get out of the tank in an hour, from a fully charged tank. There are variables. And my numbers are estimates. Let's say you have a 50g tank and the First Hour rating is 40 gallons. That means, with the tank fully heated while dormant overnight, when everyone gets up in the morning you should be able to pull 40 gallons of "hot water" out of the tank in that first hour of use. The standards have changed a bit, but in general consider "hot water" to be water within 20-30 degrees of the set point. If the heater thermostat is set at 130 degrees, you should for example be able to get 40 gallons of water between 130 and 100 degrees out of the tank in that first hour of use.

The recovery rate is another published number, it will tell you theoretically how many gallons of hot water the heater can output after it has been run down.

Other stuff to look at, what the other folk recommended:

Make sure all the valves are wide open.

If it's an electric heater, make sure if it's 220, it's wired for 220 and not 110. You'll only get a fraction of the performance out of it if it's wired improperly. If the installer installed the element in an electric heater, make sure the element is the correct size.

If electric with dual elements, there's also the possibility that one of the elements is not working.

If it has one, check the t-stat on the water heater. With it set to, say 130, make sure it hits 130 and the heater then turns off. IF the heater also has a temperature gauge on it that shows the internal water temp, open a shower and with the water flowing, watch the temp gauge on the water heater. See how fast it drops, and how far it drops before the heater cycles on again.

If still no performance, call back the person who installed it. There could be debris in the system that is limiting flow.

Small side note, but after a new heater is installed, if the water output temp is different than the old heater, sometimes the scald settings may need to be changed on the shower supply valves. Depends on the type and style of the valve, this is usually required for pressure balancing valves. For example, let's say my water heater was set at 130 degrees. When installing the shower valve, I'd run the shower valve to the hottest temp I'd want to come out of it...100 degrees, for example...and set the valve's hot/cold mixing limiter there. On pressure balancing valves it's usually a mechanical limiter, a set screw or a depth screw. If I then had a new water heater installed that put out a lower temp of water, say 110 degrees, the shower may never get more than tepid because it's expecting hotter water that it is getting, and the set-screw scald setting is limiting its ability to mix. In general, again, that's a factor with pressure-balancing valves and not with thermostatic valves. That is not your primary problem since you're getting limited water temps at your kitchen taps as well. But it is something to consider when a water heater temperature setting has been changed, especially if there are young-uns or elder-folk in the house.

A lot of writing. But it condenses down to this:

It's a new installation. Call back the installer.

Hopefully the information will give you talking points, or a bit of background that can help things move forward.

Good luck!

Also, the dip tube might be broken or have become disconnected. Your installer should take care of that.

Thank you, I'll try these things out. If you asked, the reason we had to have it replaced is because at 17 years it was also not going past 116 degrees and the inspector told us it was a health concern? No idea. I'll try all of the advice out and if we still have problems I'll try to get the plumber back.

... had the 17 year old replaced two days ago.

I would check what the temperature is set at, make sure the supply valve is fully open and if neither of those things explain, I would call the installer.

Haha thanks David. Mom brain. I wouldn't ever replace our 17 year old.

The side said we should get 65 gallons in an hour. I took a 15 minute shower last night and the water was cold by the end of it. I'll just call the guy back.

Continuity test on the elements, otherwise wired incorrect as 110 instead of 220. If elements are good and wired correctly (should be a double pole breaker) then possibly bad thermostat either upper or lower.

DavidR had good advice.

As far as safety concerns. Factory setting is 120, which still doesnt kill everything but they dont set it higher because without mitigation it would burn people. I would recommend a tank booster which allows you to set the temp to 140 on the storage tank, which allows you to really kill anything in the tank, maintain hot water longer during use, and also acts as a mixing valve to prevent scalding. That link has lots of useful info.

If the tank booster seems too good to be true, then go with a thermostatic mixing valve on the hot side before distribution to the house instead.

Side note: I have mine set to 150 and only achieve about 140, I have plumbed in temperature gauges to the cold, hot premix and hot after mix. Temp readings arent real unless you are running water for a bit, so best to check when doing a load of laundry or someone taking a shower.

Are the water lines connected backwards? The top of the water heater - inlet / outlet. When you run the hot water, the outlet pipe should get hotter.

Oh gosh I feel like this is a bit over my head. I mean I can fix basic stuff but this for whatever reason seems complicated haha. I do want the water to be safe and clean but also we have three little ones and don't want any burning accidents especially since they are at the age where they can fiddle with the faucet at bath time.

cefandl,

Look, just call the installer back. You don't need to worry about anything else unless you are getting pushback from the installer.

Set your water heater to 120-125 - no higher since you have young ones.

So here's my guess: My guess is that you have an electric water heater and the water lines are connected backwards OR the bottom element isn't working.

In order for me to get a measured 120F at the kitchen sink, I have the tank set at 130F.