How can you cakculate the cost of heating hot water in a domestic household situation?
Wednesday, July 28th, 2010 at
8:24 pm
I would like to compare natural gas to propane gas to electric water heaters in a way that is understandable to a lay person. I understand that heating water is one of the highest energy costs in a home but how would I compare the price of a tank to a tankless water heater?
Tagged with: electric water heaters • energy costs • heating water • highest energy • lay person • natural gas • propane gas • tank • tankless water heater
Filed under: Tankless Gas Water Heater
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A British Thermal Unit (BTU), is the amount of heat required to raise the temperature of one pound of water 1 degree Fahrenheit. Multiply the BTU output of the heating appliance (found on the nameplate) by the number of gallons it holds (also found on the nameplate) and multiply that number by 8.35 (The weight in pounds of one gallon of water) Tankless water heaters are instantaneous, but they have to heat cold water because they don’t have any storage capacity.
You also have to determine the cost of Electricity (sold by the Kwh), propane (Sold by he gallon) and natural gas(sold by the cubic foot) in your area and use those figures to calculate the cost of energy.
find out how much each cost….. then the amount of time both last……..
or
find out how much each cost……and then multiply that for however long you use it
I recently have been studying these calculations as part of general heat loss calculations.
Regarding tank vs tankless there are many considerations. Sometimes tankless heaters reduce flow. If you live alone and only need hot water once a day your demand is different from a family that has two showers and a bath going at once maybe more than once a day. In general tankless is better for an endless draw or a very sporadic draw. A tank system is going to be better when a batch of water is usually needed as a tank system is essentially a batch heater. 2
Heating water is considered to be the second biggest heating loss in a house behind general space heating/air conditioning. (Automotive use outside the home may be more.)
Each of these units will have an efficiency rating. This is the amount of energy that needs to be added compared to the amount that is turned into hot water. Electrical heating units are typically very efficient at making heat but they don’t have a lot of it and it tends to be expensive.
The second consideration is the cost of the "fuels" in your area. And how much heat is available in the unit of "fuel." 1
To make it meaningful you need to compare the same thing. This could be the hot water used in a month or the cost of a shower.
Your particular situation, wind levels, number of heating/cooling degree days generally and in your micro environment, insulation, occupancy, usage and even solar gain will change for each individual installation.
Because there is a level of complexity in figuring these things out there is a general rule of thumb and there are shortcuts. Often people will rely on "calculators" to do most of the math and just put in some numbers. There are informative sites and calculators below.
I’m going with breath on the wind.
The trick is not heating hot water, rather heating just water. Heating hot water is a waster of money and energy.