Is there is cost saving for you in having a tankless water heater?

I would like to know if you have experienced cost saving by switching to tankless?

If you have a whole house or just one faucet?

What brand do you use and do you like it?



Tags: garden, heaters, hot, plumbing, tankless, water

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This interests me. So a purchased unit of energy in NG is approximately 3.5 times more costly in the form of electricity, on average, currently. Has this reliably been the case historically? I know my LP pricing can vary widely from year to year. I have, possibly erroneously, thought that some years using electricity was cheaper than using propane although my previous propane supplier has proven to be criminal in their business practices. And obviously LP and NG are different creatures. And how efficiently do these different energy sources transfer that energy to our hot water? I can only assume that the vent on the NG or LP water heater exhausts some energy as well as exhaust. I would also guess that it wouldn't be enough to make up the difference. Just wondering...

That's where my thinking was 6 years ago. I thought hot water was a meaningful opportunity for energy savings, and electric water heaters were MUCH more expensive to operate.

Then I started looking at bills. At the time I was selling audits rather than performing them, so I could see as many as many as 4 energy bills a day. I tried an experiment I called "see the water heater" - where I attempted to determine the heater type by looking at the energy bill. 

I couldn't do it. When people had low electric use I'd guess gas, then go to the basement and be wrong. 

And when I did higher level analysis - attempts to disaggregate cost showed a couple things. First - hot water costs less than most imagine. Second - the true electric water heater factor over gas was about (4/3x) not (9/3x). My schema began to change.

Let's consider the savings opportunity:

  • Some would have you believe we are spending in excess of $500 on hot water. When you factor fictional savings opportunity of 3x, it starts to look like an opportunity worth exploring. I think the most I've seen is in the $300 range - when you apply a more real world savings opportunity of 1/3x do you suddenly feel victim of bait and switch? 

So WHERE did the science go wrong? Oversimplifying. Let's explore a couple direct and indirect external costs not accounted for that drag the opportunity down: 

  • Electric Hot Water Tanks have tiny fraction the standing losses of a gas tank. They have better insulation and don't have a metal chimney running up the middle that throughout the standby cycle, on a continuous basis, very effectively pulls heat out of the water and removes it to outdoors, taking conditioned air from your home with it.
  • Electric water heaters don't have dramatic decline in heat transfer efficiency as the tank warms - 1 btu electricity transfers at nearly 100% efficiency into the water at 50° and at 120°. NG heat transfer efficiency declines rapidly as temperature rises.
  • People use a lot less hot water than when the wives tale was originally formulated. Aerators, low flow shower heads, energy star appliances, efficient washing machines that clean better with colder water.

I am loathe to make recommendations real world evidence does not support. I need my predictions to be accurate. Allowing bogus hot water savings into my models will make the whole model fail. 

And NOW let's factor external costs most don't consider: 

  • Combustion appliances in the home that don't directly vent to outdoors (sealed combustion) are S-T-U-P-I-D. When they don't kill us quickly they kill us slowly. 
  • Tighter homes are more controllable, more comfortable, and more efficient. If you want a more comfortable home the smart path is to build a comprehensive plan. What is almost always included in the plan? To tighten the home. 
  • As desire to live in more comfortable homes increases what becomes more of a problem? Indoor Air Quality. VOC's may be bad for you long term, but what kills you quick? CO. What produces CO? 
  • You have to provide makeup air for the chimney that is always pulling air you paid money to filter, heat and humidify or cool and dehumidify, to the outdoors, with wasted heat from your hot water. 
  • With all those unquantified direct and indirect costs do you really want to have S-T-U-P-I-D in your house to save 15¢ a shower? Is that juice really worth the squeeze?

I am also loath to make recommendations that could kill people. To me energy savings is the result, not the driving force. Good design considers operational and maintenance simplicity, health of occupants, control, and removing impediments to future improvements.

Hopefully I've started creating a picture of why I think unsealed combustion appliances are S-T-U-P-I-D. Get rid of stupid water heaters, the real energy savings opportunities are elsewhere. Stop chasing pennies when there are dollars just as easy to grab blowing away. 

That's unfortunate, fossil methane production is between crude oil and coal for carbon-footprint, the glut of new wells is why it's cheap but the long-term affect of that will be to keep heating the ocean, the air isn't as big a deal, most of the heat is going to melting ice-sheets now and the ocean, not the atmosphere and we're gaining 34% more heat per square meter than 1990 on a steepening curve.

This is our report card, it's the greenhouse gas page and radiative forcing, aka greenhousing, costs are the wrong metric to use to deal with this:

So I guess that is the math that Ted needs to see.  Sorry Ted but I totally agree with Paul and Bob.  Of course this whole debate is completely based on local utility costs.  If you live near a hydroelectric dam and have off peak and non-tiered electric pricing it probably can be cheaper.  That's not where I live.  And as someone who has done well over 2000 energy audits I can play "find the electric water heater" and win.  In my area,homes with electric water heaters have electric bills that are double that of a NG DWH. 

I don't need to see made up math. I used to make some pretty poor conclusions using it, now I know better. 

Clocks have been used on electric water heaters for DECADES to avoid heating tanks with high cost electricity. This is nothing new that should surprise people with tou rates. 

I definitely don't need an absurd and hypothetical example of excluded middle with no expertise behind it as example that gas possibly saves less than a Starbucks coffee a week. 

I'm not saying electricity costs less, I'm saying the difference is usually irrelevant. And hypothetical situations where you game all the inputs to your advantage to justify claims of savings for a thing you sell, without any documentation to actually PROVE your self serving position, only lead to questions of integrity, not conclusions about design.

Show me the energy use and cost before on electric.

It doesn't seem like any math or anything else is going to make you feel differently.  That's fine.  That is kinda the point of websites like this - we can all agree to disagree.  As much as many of like to talk about everything we do as "building science", you can have 10 different people look at a house and find 10 different things that they think are the number one priority. 

Can you tell the houses with LED bulbs vs CFL or even Edison by looking at power bills? Are people chasing pennies in residential lighting?

Anecdotal reports on lighting have been either they change them all at once, or they change them as the incandescent fail. 

Those who change them all at once tend to report surprise at actually being able to see the savings. Obviously those who change over time don't. 

IMO, the reasons to change from CFL to LED are not energy reasons - the delta is too small. (Better light, longevity, better dimming). 

Like going to the gas pump, if you do it twice a week you get numbed to it. If you do it once a month it starts getting annoying. When you drive a Tesla and switch back for a while, going to the gas station seems a completely stupid thing to do. CFL longevity has made changing bulbs pretty annoying, and soon that perspective will shift such that it'll seem stupid not to just go LED.

Switching from Edison to LED lighting is about the same amount of energy savings as going from NG to electric water heater. NG with a tank runs about $200/yr vs $500 for electric tank. $300/yr is close to what most residential customers would save switching from Edison to LED. Is a $300/yr savings significant to you?

For some reason when I built my house all of my can lights had 100w bulbs in them, the kitchen has over 20 cans and 3 hanging lights, I did notice an electric bill change when I went to led....  About 25%...

There are other considerations that can trump this discussion, at least this is true in NY. 

The money stream funding the home performance programs comes from utility companies, mostly electric companies.  Their inspiration is reducing electric demand so they need fewer power plants.  Adding electric water heaters defeats this purpose.  Conversely, to the consumer who is looking at 1500 for a power vented water heater or $400 for an electric one and the reason for the change is combustion safety, there is  big driver toward electric.  Especially for elderly singles or couples who use very little hot water. 

Interestingly, with respect to Tankless Water Heaters, our local utility was offering rebates on power vented water heaters and higher efficiency furnaces & Boilers, but they would not give the rebate on tankless.  As has been indicated here, Tankless is much higher AFUE than power vented, so that didn't make sense to me.  I finally cornered the right guy and asked why.    I was told, the tankless units are 150000+ btu heaters,  their consumption is so high that the pipelines gas companies have in some neighborhoods could not supply several dozen of them on one pipe.  The consumers likely would not know how much supply a utility could provide to their particular branch line, so they would have no way of knowing if they were installing something that would not work.   Scary thought. 

If it is of any interest, I haven't really looked at the energy bill aspect of it, but I can tell you where I am seeing major differences in lighting loads where I have implemented low use (CFL orLED) bulbs in place of standard incandescently or halogens. I maintain the common area lighting on a couple of condominium compounds. These properties have all line voltage landscape lighting. As I replaced the standard incandescent bulbs with CFL's, I noticed a substantial improvement in the reliability of the numerous circuits in use. Pretty straightforward actually, 20 amp circuits that had previously been drawing 12 to 23 amps were now pulling more like 3 to 8 amps. All those heavily strained components and connections were suddenly bordering on under-utilized. I found myself being able to ADD lighting and still use less electricity. Clearly, the electric bills for these installations will be using SUBSTANTIALLY less than before.
I would venture to guess that any full time occupied house with more than forty bulbs and more importantly, automatic lighting, would see noticeable reductions in electrical costs from a change to low use bulbs. The key at this point is cost of bulbs. CFL's are cheap, LED's are getting there.


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