I have a 50 gallon water heater. But I'm pretty sure I don't get 50 gallons worth of hot water at a time. I think as I used the hot water, it gets replenished with cold water which gets mixed in with the hot water. So, at some point much less than 50 gallons, the water starts to get cooler coming out of the tap to the point where it's not really hot water before I've used 50 gallons.

In other words, I can't fill my tub with hot water; I need to fill to a point, wait for the water to get hot again and then fill the rest of the tub (I hate my tube; it's a stupid oval shape that's too short and shallow for my liking but uses too much water filling the oval and it only fits one person - Kohler idiots).

What size water heater would I need in order to fill the tub w/ hot water in one go? What's the effective yield of water heaters? 40%? 35%? 50%?

We went tankless a long time ago for this very reason. We can all shower and never run out of hot water. Our old 40 gallon tank only yielded about 15 minutes of shower water. Then it took at least 45 minutes before anyone could follow. I’d guess the yield was around 25 gallons.

First hr rating is 150-200% of capacity, depending on the specific water heater.

The new 50 gallon standard, atmospheric vent heaters are rated at 75 and 81 gallons.

After going through three water heaters in 13 years, we also went tankless and running out of hot water is now a thing of the past.

i put in a commercial 115 gallon water heater and solved the running out of hot water issue

How big is your tub and how many people can fit in it?

Turn up the thermostats on the water heater. The water at our house in MI is 45 degrees when it comes out of the well. With a 40 gallon water heater and family of five, we don’t run out of hot water. It think I have the thermostats set for 150. That wasn’t the case with the thermostats set at 125.

We had a 50 gal water heater that was just barely adequate in summer for our hot tub that was on the other end of the house and against two outside walls. When the weather turned cooler the supply of water wasn’t sufficient to both warm up the hot tub itself and keep the tub water at a comfortable temperature for the length of time you wanted to use the tub. Solved the problem by replacing the hot water heater with a 75 gal unit when the 50 died. Had enough extra capacity so didn’t need anything bigger.

Here are you choices as I see them

1.Crank up the temp on the heater to 150°, (cheapest)
2. Add another heater (cheaper)
3. Go to tankless (not cheap)

Your tub probably hold 90-110 gallons of water…that 50 gal heater won’t cut it unless the incoming blend of cooler water mixes with significantly hot water in the tub

I'm a little averse to tankless. Worried about hazards of something that produces so much heat at a given moment. It can probably be safe and reliable given its prevalence in asia but I'm not yet comfortable. Also not sure how well that would work with my recirculating pump. But I could consider it more.

Higher temp setpoint is also worrisome. I actually already have it set to 130F from the recommended 120F. It's kind of a hazard at other locations because the water is actually too hot - painful. 150F would be worrisome, especially if there is an accident. Also, does it have any issue with plumbing and/or appliances - can they all take the higher temp? For example, the dishwasher only has a hot water input - 150F is okay? Does this cost more to operate (gas)? Does it reduce the life of the water heater?

I was actually thinking along the lines of "pre-" water heater. Instead of another tank, what if the input of the water heater was a solar water heater (like used for swimming pools). Except much smaller capacity. Is this water still clean and potable?

My water heater is due - 20 years old now. So, trying to think about options ahead of replacement.

The tube that supplies cold water to the bottom of the heater probably disintegrated into crud that lookes like lime deposits, and you are drawing cold with the hot from the top of the tank.

Had the same problem, plus faucets, toilet valves were having problems with what appeared to be lime but was actually deteriorated parts of the water heater. Dip tube, and housings for a glass marble and a floating plastic marble meant to be check valves to SAVE energy.

I removed the dielectric fittings on the 30 gallon heater, reamed out the dip tube remains and J-B welded in a 4 ft. Pex tube from Menards. Doesn't seem to run out of hot water now.

Put in a new sacrificial anode while you are at it too.

At 20 years old you are correct to be considering a replacement.

We went with a big tankless several years ago. Couldn’t be happier. The equipment was a few hundred more than a direct tank replacement. Installation is where it can get expensive, though, as your current gas line almost certainly isn’t big enough to support a big tankless.

However, my brother and I ran a new 1” gas line ourselves as it was an easy job, saving at least another $1000.

But I won’t go back to a tank style. I love the tankless.

Current house, I have a tankless.

Old house, the previous owner had put in some super heavy duty (in terms of power, not tank size, which was fairly typical) tank heater. We had some plumbing thing done where they wanted us to run all the old water out of the tank until the water was cold. I opened every hot tap in the house and the water was still coming out hot 45 minutes later. I don’t know why that thing even had a tank.

I’m a fan of tankless gas water heaters as well but as a cheap fix have you considered insulating the pipes from the heater to the tub if you have access to them?

quote:

Originally posted by konata88:
I'm a little averse to tankless. Worried about hazards of something that produces so much heat at a given moment. It can probably be safe and reliable given its prevalence in asia but I'm not yet comfortable. Also not sure how well that would work with my recirculating pump. But I could consider it more.

Higher temp setpoint is also worrisome. I actually already have it set to 130F from the recommended 120F. It's kind of a hazard at other locations because the water is actually too hot - painful. 150F would be worrisome, especially if there is an accident. Also, does it have any issue with plumbing and/or appliances - can they all take the higher temp? For example, the dishwasher only has a hot water input - 150F is okay? Does this cost more to operate (gas)? Does it reduce the life of the water heater?

I was actually thinking along the lines of "pre-" water heater. Instead of another tank, what if the input of the water heater was a solar water heater (like used for swimming pools). Except much smaller capacity. Is this water still clean and potable?

My water heater is due - 20 years old now. So, trying to think about options ahead of replacement.

I wouldn't want the risk of someone getting burns, or wasting extra electricity, but if this is something you do once a month or week to relax, crank her up 30 minutes before bath. Especially true if you're getting ready to replace it.

No clue on size to output.

The tankless units use the same BTU as a very large furnace and they are UL tested and other testing certified so safety shouldn't be a concern. One consideration with them is it could require larger gas meter, split pressure system, and/or larger pipe runs which can add huge costs to going that route.

You are correct, incoming cold water will dilute some of the hot water. This is minimized by the dip tube that routs the incoming cold water to the bottom of the tank as hot exits the top. It is rare but the dip tube could be damaged or missing.
Easy to test for that. Turn off the power to the heater, remove the lower access cover and feel of the tank, while running a hot water tap wide open. The bottom of the tank should start out hot but turn cold pretty quickly. If it doesn't something is wrong with the tube... or even more unlikely... the heater pipes could be hooked up backwards. Yes I have seen that done more then once and in one case it was used that way for years. Feel the pipes on top as you run hot water... the ports should be labeled hot and cold, see if they match what you feel.

Water heaters used to come set from the factory as high as 155 degrees. Now much lower for energy savings and safety. Some as low as 120. I keep mine on 150 and get enough hot water to fill a standard tub from a 30 gallon tank. 120 ain't hot water, it warm water. As mentioned before turning up the temp could help a lot. Caution urged if small kids or elderly utilize it.

Another potential issue is your lower unit or thermostat not working...
If only the upper one is working you will have about half of the hot water you should. To check for that as above.. except feel the bottom of the tank a couple hours after using any hot water... it should be about as hot as where the thermostats are set. A IR thermometer comes in handy for that.

One other issue I have seen was thermostats sometimes get "lazy". Water heater thermostats do have a wide range from off to on by design but if it ranges more than about 15 degrees the thermostat should be replaced. Turn it slowly up and down and note the range between the off and on clicks.

Job #1. check the temp setting on the thermostats or measure the hot water temp at the faucet.

Is it gas or electric? If electric you could have a bad element it the bottom of your tank. Easy fix.

Thanks guys. Some great information and suggestions here. Much appreciated. I have some more research to do now.

One of the interesting things I've noticed about the gas tankless heaters is they are all 200,000 btus or greater.... that's burning a lot of gas.

When you replace your water heater, please remember that the diameter of the heaters is larger now. Some have found that the new heater does not fit in the closet or under a stair or wherever. If you have hard plumbing lines to the present heater, the height of the new heater is of import. I had to saw the legs off the platform of the old heater about one inch so that the new heater (taller) would connect properly to the copper lines.