How to tell when water heater is at max?

[wopachop]

When using the electric heating element is there a way to tell when its reached max temp and shuts off? (besides trying to listen) I keep meaning the buy an instant meat thermometer. I suppose i could test the water temp coming out the faucet. But the way the tank is designed it seems the hot water that first comes out of the top of the tank does not represent the temp of the water lower in the tank.

I notice how quickly the shower water can go from hot to cold. Seems like the tank does a good job of not letting the incoming cold water mix with the hot water at the top of the tank. Thats why simply sticking my hand under the hot water can trick ya. I did that yesterday and sure enough the water turned cold in about half the time. Thought i had waited a decent amount of time for the water to heat up.

[valhalla360]

wopachop wrote:
Correct cold water is replacing the hot water. But it does not seem to mix. Someone has posted a picture of the water heater insides. It has baffles that i believe are designed to keep the cold water from mixing with the hot.

Which goes alone with how the shower feels. Temp is normal. I feel it get colder and i turn the water handle to full hot. That lasts about 5 seconds and everything that comes out from there is cold water.

Yes, they try to minimize it by adding and drawing water from different strata...and if you are doing 0.5gal showers, it will work pretty well.

If you are using 3-5gal, there will be enough mixing to make for a noticeable temperature drop.

[bgum]

The prize goes to Valhalla. Get a killawatt or something to tell you how many watts you are pulling. When it drops about 1800 watts then the filament stopped heating.

[time2roll]

Ammeter would tell you when the electric element is on/off. If you had an EMS with display you might already have an ammeter.

[DrewE]

wopachop wrote:
I turn my water pressure down too. Just enough to make it come out.

Does anyone have a rough guess of how much propane is used to heat up the tank? There are times, like this morning, where i forgot to turn my electric element on. Wanted to flip the propane on too to hurry up the process but also hate having to go refill propane.

Not a tremendous amount of propane. Burning propane produces 91,500 BTU per gallon of propane (or 21,591 BTU per pound). Do some division with the BTU rating of the burner in the water heater to get the propane consumption per hour; the burner's BTU rating is technically a BTU per hour rating. If it's 12,000 BTU (which is the rating for the first 6 gallon RV water heater I found data on), twenty minutes of burn time would use about 3 ounces (by weight) of propane, or 1/22 of a gallon.

[Old-Biscuit]

Gdetrailer wrote:
1200W electric heating element can only put out about 4,100 BTU per hr.

Comparing that to the gas burner of the water heater which has a 40,000 BTU input gas burner and at say if the efficiency rate was only 60% conversion the water would get 24,000 BTU of heat..

4,100 electric vs 24,000 gas, you do not have to be a math genus to figure out that using gas is going to heat the water much faster, maintain the hot water temp for much longer even with extremely cold incoming water.

At a min it is going to take 6 times longer to heat the water with the electric heating element that it does with the gas burner.. Typically for my RV water heater it only takes 10 minutes or less to get scalding hot water using gas.. Mine doesn't have electric heating element but I can guess it would easily take 60 minutes or more with electric heating element only..

If you are looking for a long, long, long super hot shower on electric only, you are going to be disappointed.. Since RV electrical systems have considerable electrical capacity limitations like limiting the water heater electric element to about 1200W it is slow to heat, slow to recover and extremely fast to lose temperature when water is being drawn out..

A couple of things you can do to make the hot water in your shower last longer..

#1.. Take a "Navy" shower.. Turn on water to get wet, turn off water to lather up and turn on water to rinse off..

#2.. Do what I do, turn on water JUST ENOUGH TO GET A LIGHT SPRAY from the shower head.. Lets face it, you are not in a sticks and bricks with an unlimited supply of water and you are not going to get a shower that pins you to the shower wall if you want a long, long hot bath.. The faster you use your supply, the shorter amount of time you have to use it and the faster it goes down the drain.

Using this method, I can get a 20 minute shower with no noticeable drop in temp and 5 minutes later the next person can get a shower..

AquaHot, HydroHot, Oasis ------not the typical tank RV Water Heater

[Old-Biscuit]

Atwood uses a 1400W electric element and a 8000btu/6 gal or 10,000btu/10 gal burner (PER HOUR of Burn Time)
Heats water to 140*F where T-stat OPENS
**XT models use 160*F T-stat/Mixing Valve same 10,000btu burner

Suburban uses a 1440W electric element and a 12,000btu burner for all models (PER HOUR of Burn Time)
*4 gal uses a 9,000btu

1 Gallon of propane 91,500btu----do the math


Both use Dip Tubes on cold inlet and hot outlet
(Just like residential models)
Cold points DOWNWARD so it doesn't mix/dilute hot and creates a 'temp zone' that pushes the Hot out
Hot points UPWARD so the hottest water flows out

1400w1440w elements use roughly 11.5/12 amps @120VAC
If you have a Voltmeter installed...you can see a small deflection on voltage when it comes on and up tic in voltage when it goes off
***Amp meter would give better indication

Element when energized is 'silent' unless heavy scaling then it can 'sing'

Electric only...roughly 6.2 gal/hr recovery rate
Propane only ...roughly 10 gal/hr recovery rate
BOTH ...........roughly 16.2 gal/hr
*From initial cold temp

20-25 minutes for reheat cycle
Atwood 110*F to 140*F t-stat closes/opens
Suburban 110*F to 130*F t-stat closes/opens



IF you have short duration of hot flow:
Bypass Valve leaking thru diluting Hot out
Cold Dip tube has fallen off and Cold is quickly mixing/stirring Hot causing diluted temps
T-stat failing....opening too soon






Atwood Cartoon....no actual photos




Suburban ...bird's eye view

[wopachop]

I turn my water pressure down too. Just enough to make it come out.

Does anyone have a rough guess of how much propane is used to heat up the tank? There are times, like this morning, where i forgot to turn my electric element on. Wanted to flip the propane on too to hurry up the process but also hate having to go refill propane.

[Gdetrailer]

1200W electric heating element can only put out about 4,100 BTU per hr.

Comparing that to the gas burner of the water heater which has a 40,000 BTU input gas burner and at say if the efficiency rate was only 60% conversion the water would get 24,000 BTU of heat..

4,100 electric vs 24,000 gas, you do not have to be a math genus to figure out that using gas is going to heat the water much faster, maintain the hot water temp for much longer even with extremely cold incoming water.

At a min it is going to take 6 times longer to heat the water with the electric heating element that it does with the gas burner.. Typically for my RV water heater it only takes 10 minutes or less to get scalding hot water using gas.. Mine doesn't have electric heating element but I can guess it would easily take 60 minutes or more with electric heating element only..

If you are looking for a long, long, long super hot shower on electric only, you are going to be disappointed.. Since RV electrical systems have considerable electrical capacity limitations like limiting the water heater electric element to about 1200W it is slow to heat, slow to recover and extremely fast to lose temperature when water is being drawn out..

A couple of things you can do to make the hot water in your shower last longer..

#1.. Take a "Navy" shower.. Turn on water to get wet, turn off water to lather up and turn on water to rinse off..

#2.. Do what I do, turn on water JUST ENOUGH TO GET A LIGHT SPRAY from the shower head.. Lets face it, you are not in a sticks and bricks with an unlimited supply of water and you are not going to get a shower that pins you to the shower wall if you want a long, long hot bath.. The faster you use your supply, the shorter amount of time you have to use it and the faster it goes down the drain.

Using this method, I can get a 20 minute shower with no noticeable drop in temp and 5 minutes later the next person can get a shower..

[wopachop]

Correct cold water is replacing the hot water. But it does not seem to mix. Someone has posted a picture of the water heater insides. It has baffles that i believe are designed to keep the cold water from mixing with the hot.

Which goes alone with how the shower feels. Temp is normal. I feel it get colder and i turn the water handle to full hot. That lasts about 5 seconds and everything that comes out from there is cold water.

[valhalla360]

It's not perfect but I usually have a good idea based on our voltmeter. If you are paying attention, it will jump by a couple volts typically when the heater goes off. It's not perfect because each campground will have a different voltage and other things can move the voltage depending on what else is running but I can usually tell when a large draw is applied.

Better would be to install an amp meter on the main power inlet but it's a lot easier and cheaper to plug a volt meter into an outlet that's within easy visual range.

I would be very surprised if the temp of the water in the tank is inconsistent by more than a degree or two. The heating element is towards the bottom and hot water will tend to rise resulting in a nice mixing. What you are likely seeing is as you draw hot water out of the tank, it is replaced with cold water at a rate faster than the heating element can compensate. With only 6gal (typical hot water heater), by the time you use 3 gal, the temp can be significantly cooler.

[JimK-NY]

I would guess that it would take at least 45 minutes to heat up from cold. I never heat up the water entirely. Instead for showers I have a timer set for about 20 minutes. That is just right for a hot shower without using any cold water. That way I do no waste any water on adjusting the temperature. When I am boondocking and do not have access to water, I want to take a hot shower with no more than a total of 1 gallon of water.

[ReneeG]

I believe the light to ours, when in electric mode, turns off when it reaches max temp. Ours takes longer to heat then when in propane mode, so we rarely use the electric mode.

[2oldman]

I turn my pump off and open a hw faucet. When it starts dripping (for the 2nd time), water is hot. Of course this is using my tank.