Are tankless water heaters green?
Well, to a degree. They take up less room in a land fill. There is no storage loss from a tankless heater just sitting there. Although any heat lost by the water heater would tend to heat the room it’s sitting in. So I’m not really sure if that would actually be a waste or not.
Do they save gas? Yes, they do. You’re smiling now, but I bet your thinking that you’ll save more gas than you are going to. How can that be you say! Easy- physics hasn’t changed any. It still takes 1 btu of energy to heat 1 pound of water 1 degree Fahrenheit.
Okay- here’s how it works. Let’s say you have a tankless heater that’s 92% efficient. 1 divided by .92=1.086 btu to raise one pound of water one degree. Now lets take a standard 80% efficient water heater and do the same 1 divided by .80=1.25 btu to raise one pound of water one degree. So yes the tankless does use less gas. But because it’s a higher efficiency. Lets put these numbers to use.
Say you use 100 gallons of hot water per day. And your incoming water has to be raised 80 degrees to be at the heat you like.
The tankless would use this much gas, 1.086 x 8.33 (pounds per gallon) x 80 (degrees raised) x 100 (gallons used) =72,371 btu used.
The standard storage tanks usage would be 1.25 x 8.33 x80 x 100=83,300
Now multiply those numbers by 30 days in our month and the numbers look like this:
Tankless heater used 2,171,130 btu and the storage tank used 2,499,000 btu.
The difference is 327,870 btu. Which sounds like a lot. Wait we are not done.
You probably get billed by the ‘’thousand cubic feet’’.
Lets change the btu to cubic feet- 327,870 divided by 1000 (standard caloric content of natural gas in most areas)=327.87 cubic feet.
Lets say you pay 12 dollars an MCF (thousand cubic feet) that comes out to a dollar savings of $3.94 which doesn’t exactly cause great excitement.
So does a tankless water heater save gas, yes it does!
Does this saved gas turn into a return on investment for the significantly higher priced unit?-no it doesn’t.
Even if you allowed for a storage tanks standby loss to cause it to fire once during each night, you might save what? Well, lets say it’s a 50 gallon heater and its differential is 20 degrees when its thermostat tells it to turn on. That would mean 50 gallons raised 20 degrees like this 1.25 x 8.33 x 50 x 20=10,412 btu wasted each night, times 30 days = 312,375 or 312 cubic feet more. Or about another $3.74 at a 12 dollar an MCF rate.
So yes, tankless heaters are green, but that green may not be in your wallet!