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.
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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