By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
I’m an RV newbie with a brand new RV and zero experience, and I’ve just noticed that my water heater takes a lot longer to heat up on electricity than when it’s set on propane. Is there something wrong with it, or is that just how it works? —Penelope
Great question, and a pretty simple one to answer. There’s nothing inherently slower with an electric heating element compared to a gas-fired water heater, as long as you had enough electricity to provide way more than the 1,500 watts typically allocated for this function. It’s all about the BTU/hrs (British Thermal Units) and how many of them are supplied by your 1,500-watt element compared to your propane burner.
Here’s the definition of a BTU: One BTU refers to the amount of energy that’s required to increase the temperature of a pound of water by 1° F.
Comparing apples to apples
Since 1 watt-hr is equal to 3.412142 BTU/hr, to find out how many BTU/hrs our electric element can supply all we have to do is multiply the number of watts (in this case 1,500) by the BTUs per watt (3.41) and see that it equals 5,115 BTUs. So 1,500 watt-hrs equals 5,115 BTU/hrs. Pretty simple, right? Let’s round that down to 5,000 BTU/hrs for grins.
For comparison I looked up the BTU capacity of a standard 10-gallon Atwood propane water heater, which shows that it’s rated for 10,000 BTUs.
It’s easy to see that a 1,500-watt electric element that can supply 5,000 BTUs of heating power can’t compete with the heating time of a 10,000-BTU propane burner. So if all other things were equal, a 5,000-BTU (1,500-watt) electric element would take twice as long to raise the water temperature to the desired level compared to a 10,000 BTU/hr propane flame.
What’s the solution?
So if the manufacturers really wanted to, they could install two 1,500-watt heating elements in your water heater, bringing its heating capacity up to 3,000 watts, which equals 10,000 BTU/hrs of heating capacity. However, nobody does that since it would be using 25 amperes of current at 120 volts, which would be most of your 30-amp shore power supply.
Unless you have a large coach with a guaranteed 50-amps/240-volts of electrical power, a 3,000-watt electric element in your RV water heater is simply not practical. So you’re stuck with the fact that when your water heater is set on electric it will take twice as long to come up to temperature compared to when it’s set to run on propane. There’s nothing wrong – there’s just a lot more peak energy available in a propane tank compared to an RV shore power cord.
Everybody keep warm, safely…
Electric heating elements, such as electric water heaters, portable space heaters and even hair dryers, draw a lot of continuous power from your shore power line, which can stress a less than perfectly maintained electrical system. So never modify your RV to draw more power than it was originally designed for.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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Mike hits the hail on the head… “there’s just a lot more peak energy available in a propane tank compared to an RV shore power cord.” I always heat up the water tank with propane first, then use the electric to maintain the heat (that is..if I HAVE electricity)…
My brain hurts
If the explanation hurts people’s brains, it is way too complicated. Instead, perhaps this would hurt less.
“A campground power post can deliver 30 amps at 120 volts = 3600 watts. Manufacturers of RV water heaters typically devote about half that amount (usually 1500 watts) to electrical water heating, so as to leave some reserve capacity for other appliances. Since 1 electrical watt is the equivalent of 3.4 BTUs of heat (a BTU is a unit of heat), 1500 electrical watts will produce (1500 x 3.4 = 5100) BTUs of heat.
Over on the propane side, manufacturers of propane/electric water heaters typically equip them with 10,.000 BTU propane burners. As you can see, a 10,000 BTU propane burner out-heats a 5,100 BTU electric heater by about 2-to-1. This explains what you are seeing.”
You should check your water heater’s owner’s manual. Many water heaters allow you to run both the electric heater and the propane burner simultaneously. This greatly reduces initial heating time, and boosts the recovery rate when you use a lot of hot water – in the shower, for instance. When you are done with your shower, just switch off the propane burner, and use electricity to maintain the water temperature.
But I’m a teacher and always have to show my work. If I don’t, my students get lazy and copy off one another. 😁
If you have a motorhome, another option is an engine-assist hot water heater that uses waste-heat from the engine to provide”free” hot water. Coach House uses these in their E450 lineup. Not aware of any others using them as standard equipment but readily available in the after-market.
Winnebago has that feature. There’s also “coach heat” that includes a blower and outlet vents in the cab and elsewhere that warms from engine heat. I don’t know if they’re still including these features in newer rv’s.
There is a possibility that depending on the Age of the RIG, the Water Heater Element could be going bad and may need service!
If her water heater is taking along time to heat up, say 6 or 10 gallons, could be the element or the circuit board too.
As a plumbing contractor a heating element either works or doesn’t work. There’s no in-between.
There’s a third possibility if the hermetic seal is breached, allowing water to make direct contact with the actual element. That can leak 1 or 2 amperes of fault current to the vehicle ground. But that can only cause a hot-skin contact voltage if the RV ground through the pedestal is corroded or otherwise disconnected. And in 240-volt water heaters that only switch one pole, the heating element will never shut off, getting the water in the tank to the boiling point, blowing off the overpressure vent, and running up your electrical bill. Been there, done that… 🔧
If we have a choice, and we almost always do, we choose to use electric. We can come into a completely cold RV and turn on the water heater and take a shower 30 minutes later. Seems pretty fast to us.
We had a 2002 Mountain Aire with a 10 gal water heater that we used the electric 90% of the time. If we wanted to take our showers in rapid succession we turned on the gas when we started the first shower and by the time our shower was finished and all the drying off time, approximately 15-20 minutes the water was hot for the next one, then we turn off the gas.