water heater vs tankless

drhvac

Anybody know how to estimate the difference in savings between the two? A water heater has an energy factor of about .62, and a tankless has an energy factor of about .82. How do I calculate the savings? I have an engineer for a customer, and the guy wants to see everything on paper before he makes his decision.

bob eck

gas water heaters

Go to a web site like Noritz www.noritz,com and sent them a email. The tankless water heater companies tell you their units save money because they only use gas when hot water is needed. Tankless gas water heaters should never run out of hot water and if serviced annually they should last 10 - 15+  years most have 12 year heat exchanger warranty. I would sell TGWH on the benefit that they never run out of hot water and on how long they should last.  If going tankless make sure the gas line is large enough. Re piping the gas line is a expense that needs to be addressed when selling TGWH. Take a look at the A O Smith www.hotwater.com Vertex 50 gallon tank type water heaters. They have two 50 gallon models that have a thermal efficiency of 90% & 96%. These units have a 6 year warranty. The Vertex 50 gallon model delivers more hot water than 75 gallon tank type and the GPHE-50 is only 76,000 BTU input and in most home the gas line should be large enough with out re piping it and making it larger.  No matter if you go TGWH or tank type if the home owner has hard water and does not treat it the hard water will increase their hot water energy costs by 25% - 30% in a short time. On the tank type unit you can make it last a lot longer than 6 years by replacing the anode rode every year and flushing the tank out two to three timer per year.

Paul48

Provide

him with this http://www.rinnai.us/tankless-water-heater-energy-savings-calculator/

Harvey Ramer

Consider it this way.

Calculate the BTU requirements to raise the water temp 70 F at 5 gpm. GPM = BTU/h devided by delta t  time 500.  Your BTU load is 125,000 for the tankless. Now remeber, depending on the home owners habits, a large percentage of the time he will be using less than 5 GPM. This will greatly affect the efficiency of the tankless.



On the other hand, the above mentioned AO Smith, will remain at it's efficiency ratings regardless of usage.



If the home owner has a big old garden tub, you may want to consider the tankless. Otherwise i'd stick with something a little more dependable.

Paul48

energy factor

You can't use energy factor unless you are comparing the same animals.They can't be tested the same way, so it's like comparing a water heater to a washing machine.

Harvey Ramer

No disrespect, but I disagree

with you. Both machines are eating gas to provide an adequate supply of DHW. You would probably fill up a whole book with formulas and math to determine which uses the least amount of energy to get the job done.



Like I said before, I think it largely depends on the usage habits of the home owner.

Paul48

OK

Then what would the stand-by loss be of a tankless, because that is used for determining the energy factor of a conventional tank water heater. There is no consideration for different animals, and it may take a book to properly determine the difference in efficiency from one to another.They take like animals and score them based on their characteristics.I didn't make that up,or make the rules. That's just how they do it.

HDE

To interject

Paul and Harvey, both of you are missing part of the equation.



EF is more than standby loss. It includes 3 factors, all playing a part in the higher EF of a tankless. Go with a condensing appliance and the recovery efficiency is higher raising the EF.



Recovery efficiency – how efficiently the heat from the energy source is transferred to the water

Standby losses – the percentage of heat loss per hour from the stored water compared to the heat content of the water (water heaters with storage tanks)

Cycling losses – the loss of heat as the water circulates through a water heater tank, and/or inlet and outlet pipes.



The formula was a bit off too



5gpm x 70 degree rise x 8.34 x 60 = 175,000



Combustion efficiency can't be confused with energy factor, however with tankless its usually within a point or two.

Harvey Ramer

My bad on the formula,

I redid it and came up with 175,000 BTU. I did it with a calculator this time instead of in my head. Must be losing it.



I guess you could probably argue all day about whether the tankless or convention water heater is better. Since we are already on the subject, why don't we throw in a heat pump water heater and an indirect water heater. The indirect, I know for a fact, only loses 1 deg F per/hr, That is so long as you put it where water heaters go and you heat the water inside to a normal temp.