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Two Water Heaters in Series

Q: I want to change my method of heating water for my home. However, I'm getting confused as I discover all the different ways that a household can produce hot water.
Which method is best for me?

A: The best method for you will definitely have to take into consideration your lifestyle as it pertains to living in your home. So you and I would probably need to talk before I could suggest an appropriate system. But we can get started by presenting some of the more commonly used methods of residential water heating.

Electric Tank Water Heaters

These units are extremely popular and are basically the same today as they've been for many years with one MAJOR exception. About 15 years ago, water heater manufacturers started switching from fiberglass insulation that surrounds the tank to foam insulation. This resulted in a much more effective capability in keeping your water hot for a much longer time and dramatically reduced the cycling on and off to reheat the water in the tank when no one is home to use hot water. In fact, the foam insulation is so effective that your cost for having hot water will be primarily based on how many gallons of hot water you use, not how many gallons are on standby.

Foam insulation allows two 40 gallon or two 50 gallon electric water heaters to be installed in series, elative to flow of water (see schematic below), providing more gallons of hot water with very little change in your monthly electric use. If your household needs a large quantity of hot water or has a whirlpool tub, this strategy works well. These water heaters are very inexpensive to buy and safe to operate. Most builders today have adopted this two water heater strategy because it solves a lot of hot water issues for homeowners, such as:

  • Plenty of hot water is readily available.
  • Water stays at 120 F for a long time.
  • Quick recovery is no longer an issue.
  • Cost of hot water is primarily determined by how much water is used not by how much is stored in the tank of the water heater.
  • There is no potential for back drafting, as with gas models.
  • There is no loss of conditioned air from the home through a flue, as with gas models.

Geothermal Heat Pumps

If having the lowest operating cost to produce hot water is your goal, geothermal heat pump technology should be on your list of methods to research. Most of your summer use of hot water is a free by-product of cooling your home. The heat that standard air conditioners would remove from the inside of your home and transfer to the outside air is instead put into your water heater with a geothermal heat pump.

These units also produce hot water in the winter, but may have to be partially backed up with your conventional electric water heater to produce all the hot water you may need.

If you are building a new home or replacing the heating and cooling system in your present home, geothermal technology is a strategy worthy of your consideration. It's a more expensive system to purchase, but is the least expensive way of heating water for your home.

Tankless Water Heaters

These units would at first seem to solve the problem of running out of hot water, because they produce it as needed or "on demand." There are some home situations that make this technology a better choice for simple installation. However, to produce hot water continuously as needed requires either an extremely large heating unit (compared to the heating capacity of a residential furnace) or a reduction in the volume of water flowing through the unit to allow sufficient heating of the water. The units with large heating capacities are more expensive to purchase than the standard tank type water heaters and use a lot of power while running. The smaller capacity units don't provide the volume of hot water flow that most people expect.

Neither size actually provides instant hot water, but they do have some space saving features due to not having storage tank.

Gas (LP or natural) non-power vented tank water heaters that require double wall metal flue pipe

These units must be vented with a flue that goes up through the roof of the home. When operating properly, these units will heat water a little faster than electric models. But this small advantage is negated when the two electric tank type water heaters are installed in series.

These gas units in today's tighter constructed homes introduce a back drafting risk that wasn't as much of a concern in the past. The flue is more often the easiest pathway for makeup air to get into you home. Makeup air is the air that comes into your home to replace the air your clothes dryer, bathroom exhaust fan, range hood vent or whole house vacuum system sucks out of your home. When this makeup air gets back into your home by way of the flue pipe of your gas water heater, it has the potential to bring with it flue gases which may include carbon monoxide back into your home.

A gas water heater that doesn't have this back drafting potential is a unit that has a sealed combustion chamber and a power vent. These units are safe in today's tighter homes and are actually more efficient than the non-power vented water heaters just discussed. These power vented units do cost more, but their safety features make them a much wiser choice.

Because different families have different hot water needs, we may not have addressed all your concerns in this discussion of water heater types. Feel free to call me at 738-4115 or 951-2323 to discuss your situation and needs more specifically, so you can make an informed decision for your home's water heating strategy.



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