I have a suburban 10 gallon gas and electric hot water heater. I just discovered my electric element burnt out, and in fixing it a question arose in my mind. I like to have both heat sources on so recovery is faster, but I realized my electric element was out because I began to notice how often my propane burner was burning. What I want of course is for the electric element to do all the regular maintaining of the temperature and for the propane to kick in only when water is being used in a large amount. I don't want to unnecessarily drain my propane tanks. And it seems that's what my water heater does, because I only noticed the propane on a lot when my electric element burnt out. Is it true then that when the thermostat calls for the water to be heated a little bit that first the electric element comes on? Does the propane not kick in unless there is a higher demand? Or does a drop in water temperature cause the thermostat to just kick on both the element and the burner? Is ther a sequence designed into the system? Or do I have to turn the propane off to make sure that anytime the water temp falls a little that only the electric element will maintain temperature?

Two completely different sets of T-stats...but both are pre-set the sameOne 120V AC set (normal and ECO) for electric elementOne 12V DC set (normal and ECO) for propaneBoth normals are pre-set for 130F (turn off temp) and both ECO (high temp) are pre-set for 170*F (turn off temp)You can get a lower pre-set......120*F Or a higher pre-set.....140*FHigher pre-set for electric.......both propane/electric would come on. Propane would shutoff at 130*F and electric would continue operating until 140*FDISCLAIMER:Not sure of temp that t-stats close at. (Typically 30*F spread from close to open)If the same open/close range for t-stats then the higher pre-set t-stat would close 10*F before the other and open 10*F higher than other.Soooo propane may not come on at all when using electric & propane with different temp t-stats due to the same open/close range?????Probably easier to run both until water is heated then turn propane off and let electric maintain. Then kick propane back on for fast recovery.....if needed.We use electric only when we have AC power and save the propane for when we don't have AC power

On my Suburban 10 gallon WH...I always run on 110 when I can....the very few times I have needed more hot water...I just turn the propane on and it runs for a very short time then shuts off and the electric keeps the temps up.I very rarely use the propane with the 10 gallon WH. Never have run out of hot water on electric even with a 15-20 minute shower.

I don't believe there is ANY relationship between LPG and 120VAC. You select Either Neither or Both and it does what it can do. Including running both till one t'stat is satisfied, then the other. It seems from what you say that the LPG thermostat is set (translation: Built - Don't think they're adjustable) higher than your electric t'stat. AFIK the "standing pilot" LPG heaters use an adjustable t'stat but the DSI types do not. Also, none of the OEM electric t'stats seem to be adjustable. If you want LPG "backup" for your 120VAC operation I think you'll have to turn it on yourself.Our coach is 30A, and we often find we can't run our 15K A/C and the WH on Electric in the summer. I've found that the DSI LPG feature provides hot water so quickly, that not having a full hot tank from 120VAC operation isn't really a problem. I can turn the WH on partway through a meal and have plenty of HOT water for dishes. 10-minutes or so.

Who is paying the electric bill. If you than propane is about 3 times cheaper. If included in your camp fee, the go with electric or both. Thermos are not adjustable so really either one could start or run first. Forget about it and enjoy camping. Don"t sweat the small stuff.

It's not the cost but the fact that I have to go get the bottles filled and if it's cold enough it shortens my furnace capacity. When plugged into the campground it just seems better. I just began to wonder and came to the conclusion that a staged set of thermostats would have been a good engineered setup. It would only take a few degree differential, but it seems from what folks have said, it's not the case. Too bad.

Sequence of electric and gas operation in water heater

j-d
Explorer II
Nov 15, 2013
I don't believe there is ANY relationship between LPG and 120VAC. You select Either Neither or Both and it does what it can do. Including running both till one t'stat is satisfied, then the other.

It seems from what you say that the LPG thermostat is set (translation: Built - Don't think they're adjustable) higher than your electric t'stat. AFIK the "standing pilot" LPG heaters use an adjustable t'stat but the DSI types do not. Also, none of the OEM electric t'stats seem to be adjustable. If you want LPG "backup" for your 120VAC operation I think you'll have to turn it on yourself.

Our coach is 30A, and we often find we can't run our 15K A/C and the WH on Electric in the summer. I've found that the DSI LPG feature provides hot water so quickly, that not having a full hot tank from 120VAC operation isn't really a problem. I can turn the WH on partway through a meal and have plenty of HOT water for dishes. 10-minutes or so.
cpaulsen
Explorer
Nov 15, 2013
On my Suburban 10 gallon WH...I always run on 110 when I can....the very few times I have needed more hot water...I just turn the propane on and it runs for a very short time then shuts off and the electric keeps the temps up.I very rarely use the propane with the 10 gallon WH. Never have run out of hot water on electric even with a 15-20 minute shower.
Old-Biscuit
Explorer III
Nov 15, 2013
Two completely different sets of T-stats...but both are pre-set the same

One 120V AC set (normal and ECO) for electric element
One 12V DC set (normal and ECO) for propane

Both normals are pre-set for 130F (turn off temp) and both ECO (high temp) are pre-set for 170*F (turn off temp)

You can get a lower pre-set......120*F
Or a higher pre-set.....140*F

Higher pre-set for electric.......both propane/electric would come on. Propane would shutoff at 130*F and electric would continue operating until 140*F

DISCLAIMER:
Not sure of temp that t-stats close at. (Typically 30*F spread from close to open)
If the same open/close range for t-stats then the higher pre-set t-stat would close 10*F before the other and open 10*F higher than other.
Soooo propane may not come on at all when using electric & propane with different temp t-stats due to the same open/close range?????

Probably easier to run both until water is heated then turn propane off and let electric maintain. Then kick propane back on for fast recovery.....if needed.
We use electric only when we have AC power and save the propane for when we don't have AC power

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