Seeking independent studies re tankless vs tank systems.

JohnNY

Good morning. I'm trying to educate myself about the highs and lows of tankless water heaters. Please point me toward any independent studies you know of that are non-biased and helpful.
Thank you!

Hot_water_fan

In regards to natural gas heaters, the frequent starts and stops of tankless heaters can lead to high methane emissions, but according to this study, the average emissions are still slightly lower than a gas tank.

https://news.stanford.edu/2020/04/17/water-heaters-methane-leaks-high-fixable/

mattmia2

There are a lot of ways to cut it even if you are trying to be unbiased. Do you only look at properly engineered systems? Do you look at everything out there? What about reciruclation loops and total water usage, how much water gets wasted trying to get hot water.

Larry Weingarten

Hi, Here's a link to some past "Hot Water Forums" put on by ACEEE: https://www.aceee.org/events/archive It will take some digging, but there is a lot of info there.

A few biased comments... I'm a fan of simplicity and modern tankless aren't. I'm the guy people call when they have hot water problems and I've had lots of calls about tankless heaters. As for efficiency, condensing tank type heaters are right up there with condensing tankless but have less upkeep. In the US we seldom maintain water heaters even if we would benefit by doing so. Complex heaters need maintenance, but getting people to change is hard. So, I feel that tankless has a place, but should not be oversold.

Yours, Larry

JohnNY

Larry Weingarten said:

Hi, Here's a link to some past "Hot Water Forums" put on by ACEEE: https://www.aceee.org/events/archive It will take some digging, but there is a lot of info there.

A few biased comments... I'm a fan of simplicity and modern tankless aren't. I'm the guy people call when they have hot water problems and I've had lots of calls about tankless heaters. As for efficiency, condensing tank type heaters are right up there with condensing tankless but have less upkeep. In the US we seldom maintain water heaters even if we would benefit by doing so. Complex heaters need maintenance, but getting people to change is hard. So, I feel that tankless has a place, but should not be oversold.

Yours, Larry

Thank you, @Larry Weingarten. I've been saying similar things for years but advising, even casually, against tankless water heaters is frequently met with an inexplicable level of pushback and scorn. After a while I begin to doubt myself and I'm trying to stay current on any new information about such things.

mattmia2

Tankless water heaters get a lot of marketing, ultra high efficiency tank type ware heaters don't. Conventional tank type water heaters are inefficient because of their 1940's burner and heat exchanger design, not because of the tank.

Hot_water_fan

Tankless water heaters get a lot of marketing, ultra high efficiency tank type ware heaters don't.

Right on. In Louisiana, they're treated as a premium product, yet our incoming water is like...80 degrees so they provide few benefits.

Steamhead

mattmia2 said:

Tankless water heaters get a lot of marketing, ultra high efficiency tank type ware heaters don't. Conventional tank type water heaters are inefficient because of their 1940's burner and heat exchanger design, not because of the tank.

They've gotten better over the last couple decades. But, as @Larry Weingarten says, people don't maintain them. When the bottom of the tank is covered with sediment, heat transfer is impaired.

We recommend installing whole-house sediment filters for this and other reasons. But these have to be maintained too...............

Ironman

Depending upon the hardness of the water, tankless can lose efficiency quickly and require much more maintenance than tank heaters. When those costs are factored in, a tankless can actually be more expensive to operate than a tank.
Ive got extremely soft water because our aquifer goes through a large sand bank; however, just a short distance west of here, the water is very hard. I won’t even consider offering a tankless in that area.
I can’t remember the source, but a few years ago someone did a study and found on average that a tankless only saved about $36 per year in operating costs. Factor in the higher installation and maintenance costs, and in many cases, the customer is worse off financially than with a tank heater.

GroundUp

I swapped out a 15 year old natural draft 40 gallon WH for a new Rinnai tankless in one of my rental homes a couple years back, as the hot water usage there at the time was primarily showering for 9 farm workers. I figured it would be a good fit for a tankless, being near constant usage for a couple hours every day with very little in between. That house has a shallow well with naturally soft water plus a whole house filtration system, so maintenance is pretty minimal, but there is SO much waste in waiting for hot water (not a big deal being supplied by a well) and the actual fuel savings was only a couple bucks a month versus the old natural draft unit. For an average household, no matter the water quality, I find a tankless of any sort to be a losing venture from all aspects. One would be money ahead from start to finish with a tank unit, always. Vacation homes, garages, wash bays, showerhouses, etc are all good places for a tankless or a very large household with a ton of hot water usage can definitely benefit from the extra efficiency but for the average 2-5 person households it's unlikely that the savings will ever pay for the unit IMO.

JohnNY

Can anyone attest to the typical thermal, as opposed to seasonal, efficiency of tankless units?

tim smith

We have been against tankless for years as we are the ones who get called in to fix them when there are issues. So many people installing them but don't service them. I may be swaying a little bit on my thoughts about them as they are overall pretty reliable now. Just really dislike having to tear them down. So many parts and pieces to take apart just to get to other parts that are causing problems. If someone worked on units regularly they would become more efficient at it but still its a pain.
Just my .02 worth
T

SlamDunk

https://www.consumerreports.org/water-heaters/tankless-water-heaters-vs-storage-tank-water-heaters/