We rarely see single-element residential water heaters anymore, except in older mobile homes and Park Model RVs. Their only advantage is that they are usually less expensive to buy. Dual-element water heaters are rated as more energy efficient and have a faster recovery time.
But, although dual-element water heaters have two elements, only one of them operates at a time. The top element comes on first and, when the water at the top of the tank has reached the temperature setting for the top thermostat, then the bottom element kicks in until its thermostat is satisfied. See our blog post What is the difference between a single element and dual element electric water heater? for more details.
Most single-element water heaters that are 30-gallon capacity or more can be replaced with a double-element one. Water heaters with a tank smaller than 20-gallons are always single element. Just check for these three sticking points first:
1) Most single-element water heaters are rated for 120-volts, whereas dual-element water heaters are 240-volts. If the circuit breaker for your current water heater takes up only one slot in the electric panel, it is 120-volt. There may be some 120-volt double-element water heaters out there, but we have never come across one. So you may have to stick with a single-element water heater for replacement if that’s the case, unless you want to rewire for 240-volts.
While it is possible to connect at 240-volt water heater to 120-volt wiring, it’s not a good idea. Check out our blog post Can you wire a 240-volt water heater with 120 volts? for a full explanation.
2) The height and width of the available space is often an issue in water heater replacement. Make sure the new 240-volt unit fits the available space.
3) Also, mobile home water heaters are plumbed on the side instead of the top. Our blog post How can I tell if a water heater is HUD-approved for mobile/manufactured homes? explains this difference further. Many local building departments do not enforce the requirement for a HUD-approved replacement water heater, but you don’t have to reconfigure the plumbing connections if you stick with a HUD-approved one.
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Here’s links to a collection of more blog posts about WATER HEATERS:
• Are water heaters required to be raised off the floor?
• Can a Temperature and Pressure Relief (TPR or T&P) valve be mounted to discharge horizontally?
• Where are gas water heaters not allowed to be installed?
• Is the minimum size water heater inlet pipe 1/2" or 3/4" according to the building code?
• Can you use a light switch for a water heater disconnect?
• How can I tell if a water heater is HUD-approved for mobile/manufactured homes?
• Can you wire a 240-volt water heater with 120 volts?
• Is it alright to have a shut-off valve on both the hot and cold water pipes at a water heater?
• What is the minimum clearance to doors and windows for an outdoor tankless gas water heater?
• What is required clearance for access and working space in front of an electric water heater?
• Why is the water heater older than the house?
• Does a water heater need a shut-off valve?
• Why should a tankless water heater have an isolator/service valve kit installed?
• When was a gas water heater first required to be elevated 18 inches above a garage floor?
• Can the temperature and pressure relief (TPR) valve discharge pipe for a mobile/manufactured home water heater terminate under the home?
• What is the purpose of a thermostatic mixing valve above a water heater?
• Does a tankless gas water heater still work with no electricity during a power outage?
• Why do water heaters have a sacrificial anode?
• What is the difference between a manufactured/mobile home water heater and a regular water heater?
• Does a tankless water heater require a pressure relief valve?
• When is a water heater drain pan required?
• Why is there water in my water heater drain pan?
• What does it mean when a water heater Temperature/Pressure Relief (TPR) discharge pipe is "trapped"?
• Can I leave a gas water heater in place when remodeling a garage into a family room or bedroom?
• Where do I find the water heater in a mobile home?
• Does a tankless water heater in an attic require a drain pan?
• Does an electric water heater require a disconnect?
• Is a catch pan and drain piping required for a replacement water heater?
• What is the difference between a single element and dual element electric water heater?
• What is an FVIR water heater?
• What is a heat pump water heater?
• What is a dielectric union?
• What's that powdery crust on the pipe connections at the water heater?
• What are the most common installation mistakes with water heater replacement?
• Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises?
• What can I do to make my water heater last longer?
• How can I determine the age of a water heater if the serial number is missing or decoding it is impossible?
• How does a hydronic heating system work?
• What is the difference between a regular water heater and a direct vent water heater?
• What is the difference between a regular water heater and a power vent water heater?
• What is backdrafting at a gas water heater?
• How do I determine if a water heater is gas or electric?
• What does it mean when a gas appliance (water heater, furnace, or range) has been "red tagged"?
• What's the valve with the flip-up handle on the water heater for?
• Why is an older water heater an insurance problem?
Visit our WATER HEATERS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.