tankless -vs- conventional hot water heater

KMD

I have a 30 year old convential hot water heater in my house, 3 people live in the house normal hot water use should I think about the new tankless heater or replace with convential 60 gallon which I have now. Are the tamkless ones more efficient, will my bill be less? what are the pros thoughts on the tankless heaters.

Next question what brand tankless or convential heater would you buy?

Dave Yates (PAH)

Hi-e

Both varieties can be had in high efficiency (up to 99%) models or "standard" efficiencies.

You've got more homework to do to correctly match an on-demand water heater to your home that you will with storage types & the main consideration centers around the peak load your family will need. Be careful not to buy into the stated flow rates unless you do the math regarding net Btu inputs and GPM flow rates with the coldest inlet water temps you'll be seeing. For instance: if you raise a gallon of water 100 F, that requies 833 Btu's. If you need an 80 degree F rise, that's 666 instead.

Let's say you've decided the peak load is 3.5 GPM. If you need the 100 F rise, the net input of the on-demand must be a minimum of 174,930 Btu's. At an 80 F rise, that works out to 139,860 Btu's per hour net input. More than a few of the current ads for on-demand water heaters are stating much higher GPM flow rates, which can't be supported if your coldest incoming service line temperatures fall below 55 F and you want the deliver temp to be at least 102 F (too cool for my tastes, because you'd be using only the hot side for delivery). I'd want no less than 120 F (in reality I want 140, but that's another story), which then means my cold water delivery can't fall below 70 F if I'm to meet the stated flow rates. Not exactly real-world conditions.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mike T., Swampeast MO

Definitely more efficient and likely longer lasting.

Main drawback is that flow is rather limited and colder incoming water in the winter will take a significant toll as well. Larger units are available but cost starts to climb rapidly and (if electric) may require extensive re-wiring to accommodate the large load.

If you're willing to spend some research time and can make a good estimate of the peak load and have a good estimate of your incoming water temps you can find out on the web if a model is available to meet the load and budget. If not willing, find someone familiar with them and ensure that you don't low-ball your estimated flow requirement!

If you or someone in the house likes hot showers (length doesn't matter) I'd honestly measure the water temp when you're showering. While I find it scalding, one member of my household will take 125°+ showers!

Jack_21

Rinnai Continuum

On demand water heaters are all about flow and temp rise. Check your incoming water temp. If you check www.rinnai.us you can see actual flow vs temp rise chart. With the model 2520FFU I use a 50F input (yes, it may vary a bit thru the year) and 70F temp rise delivering 4.5gpm of 120F hot water. Get a bucket and time the flow rates of your fixtures to be sure. In my home I can run two 2.5gpm shower heads 24 hrs per day if I want to. If someone opens another tap the water pressure will decrease but the output temp of the Rinnai will remain the same.

You cannot bathe in more than 105F and your themostatic shower valves are set at 112F. 120 is sufficient for everyday use, IMHO. Should you desire higher temp the Continuum can deliver up to 140 by simply pushing a button.

Personally, with the performance of my Rinnai, I cannot imagine why I would want to store hot water and keep it hot when everyone in the house is either at school or at work.
I cannot afford that.

Larry Weingarten

what's best?

Hello: If you're looking to go tankless on $ savings alone, make sure to look at the entire $ picture. There will be a cost to pay to install one over what simple tank replacement would cost. You may need to increase the gas supply. You will need to put in a bigger vent. The tankless heater will need regular maintenance. If you have hard water it will need to be de-limed periodically or efficiency will fall off quite a lot. You should also look at what that extra expenditure could make in the meantime as an investment elsewhere. Money market rates are creeping up.. just saw 2.25% (whopee!) Equipment life is another question. As a rule of thumb, conservation costs about 1/3 what energy production does. So, proper heater placement, low flow fixtures, piping sized to handle the flow and no more, plastic piping to rob less heat from the water, insulation on all hot plumbing, manifold piping, GFX heat exchanger/s... These things may be $ well spent to cut down on the hot water demand. Hope that helps.

Dean_7

tankless

Follow this link:http://www.askthebuilder.com/451_Tankless_Water_Heaters_-_Some_Surprising_Facts.shtml

From Hot Tech Topics Water heater Rescue right here on the wall

Dave Yates (PAH)

Tim should stick to what he knows - pounding nails.

"110F hot water is 8 degrees below the temperature that most adults feel pain (the average shower temperature for most adults is anywhere between 115 - 120F)."

Wrong - 106 F is the human threshold for pain. If you remain in 120 F water for 5 to 8 minutes, you can expect to receive 3rd degree burns.

"Unless I am mistaken, it would cost 3.5 times more money to use this heater in my home."

Yes Tim, you're mistaken - again.

"It is astonishing how much mis-information is out there."

Well, Tim nailed that one on the head!

He does makes some good and valid points regarding flow rates.


To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Dean_7

temps

Dave is right about the temps. The purpose of the wall is to educated and inform. That's why I posted the link. Scalding is a serious issue.

gehring_3

Tankless vs. Separate Tank

Going back to the original question...I have both. I have a tankless coil on my steam boiler and a separate A.O.Smith electric hot water heater. I piped them with a series of ball valves in such a way that I can get hot water 1.) off the tankless alone, or 2.) off the hot water heater alone, or 3.) from the tankless then into the hot water heater (like a holding tank). I like this system because I can still get hot water if I have to shut my boiler down for any reason. Also, under option 3 (from tankles into hot water heater) I can have a house full of guests taking showers and we never run out. It works for me.

michael_15

temperatures - an additional comment

I might add in addition to all of these 100-120 F temperatures that your dishwasher likely wants 140 F, or, if it's a good one, may demand 155 F. It's probably not reasonable to ask for 155 F inflow (serious overkill), but the standard FDA safety temperature for washing dishes is 140 F.

-Michael

Boston Boiler

Thats a back up you got going there gehring. Why not, same idea as the A-B switch on your electrical panel to go to a generator. I prefer cold start with an indirect but like you said, my boiler goes down I'm without hot water all together.

BB

Dave Yates (PAH)

most dishwashers

on the market today have an internal heater to raise the rinse water to 140 F+. They adapted following the industry-wide effort to lower unitrol settings to 120 F many, many years ago.

It's interesting to note that the food service industry recognized - even way back then - that 140 F was needed to combat bacterial amplification.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"