Posts Tagged ‘tankless water heater’

Tim Carter Says No Body Slams

Jul 19, 2007 |  by  |  Craftsman Archives  |  Share

Tim Carter emailed and had a problem with the photo in my last entry of him getting body slammed:

I will respond in a few days on your blog. The first thing I will address is your copyright violation…… of the mashup of the photo. If you want to take that photo down before I post, it might save you a little pain. simple smile Tim Carter Says No Body Slams I am very involved in a top-secret project right now and simply don’t have the time to deal with it.

I updated the photo to reflect his request. What a shame. On the positive side, I got my first copyright take down notice ever. In celebration I’m going to go hire a lawyer.

Seriously though, I am honestly interested in discovering what the truth is behind the tank vs. tankless debate both for my sake and everyone else out there reading. I’ve heard convincing arguments on both sides and am left feeling completely unsure. I look forward to Tim’s response. I have no doubt whatever he says will cause my engineer friend to blow like TNT, so I’ll probably have a follow-up should Tim decide to throw in his two cents.

Oh, the joy of blogging.

Tank vs. Tankless Revisited: Tim the Builder Gets Bodyslammed

Jul 19, 2007 |  by  |  Craftsman Archives  |  Share

bodyslam3 Tank vs. Tankless Revisited: Tim the Builder Gets BodyslammedIf you remember, I wrote this entry a few days back in an attempt to shed some light on the tank vs. tankless water heater debate. Tim Carter, a nationally syndicated newspaper columnist, explained in a 2002 article that in many situations, tankless water heaters may not be as efficient as they claim. Since that article he’s received emails from individuals verifying his claims – even up until last September. I discussed this with my neighbor the other day who happens to be a mechanical engineer that specializes in HVAC systems and though I know engineers can be a little off the wall sometimes, I had no idea how furious he would get after hearing me summarize Tim the Builder’s claims. He went off slinging calculations and quotients until I had to gently interject with the ol’ slow-it-down hand motion and remind him that I was just the messenger and that if he wanted to battle this out mano a mano with Tim the Bad Boy Builder, I had the perfect place for him to throw down. So here he is in all his glory. I’d love to know what you think.

Holycow, this Tim guy is out of his mind on every level.

1. First, he claims tankless can’t keep up with the flow rate demand. He uses an example of a unit that can deliver 3.8 GPM (gallons per minute) at a temperature of 110 F. Note that there is one vital piece of information missing; what is the entering water temperature? To be able to make any calculations you would need to know the temperature rise that the unit is capable of. Anyway, his claims of flow rates of the various fixtures in a house are correct, 2.5 GPM for a shower head and 1.5 GPM for a faucet. But one thing he forgets is that you don’t take a shower without tempering the hot water with the cold. Therefore, a shower will not use 2.5 GPM of hot water. If we knew either the temperature rise capability of the unit or the entering water temperature I could tell you exactly how much hot water you would use at the shower head. But also to do that we would have to assume a desired shower temperature.

2. That leads us to the next item that he’s all wet on. He claims that most adults take a shower at a scalding 115 to 120 F. Why don’t you try a shower at that temperature and let me know how quickly you scream in PAIN. Maybe I’m a wimp but when I get in a hot tub, like the kind at an expensive resort, at 103 to 105 F I can only stay in the tub for about 10 minutes. Here is some more concrete data: the threshold for PAIN is between 106 and 108 F, and expect a third degree burn in from water at 110 F if exposed for 10 hours, raise the temp to 120 F and expect the same burn in only 10 minutes, raise the temp to 130 and get a third degree burn in only 30 seconds, shall I go on?

So let’s add these two items together and see what happens. But we need, again, to make some assumptions: earth’s average below grade temperature is 55 F and therefore the entering water temp (EWT) is also 55 F, the temperature rise capability of the heater changes with flowrate (GPM) and might look something like this:

90° F rise / 2.1 gpm
77° F rise / 2.4 gpm
65° F rise / 2.9 gpm
55° F rise / 3.4 gpm
45° F rise / 4.3 gpm

So it follows that if I wanted a shower at a deadly 132 F, I would simply turn on the hot water all the way – remember U.S. shower heads are governed to be 2.5 GPM – and not temper the water with any cold water. 55 EWT + 77 F temp rise = 132. Yep, seems to be working okay so far.

Okay, so lets say I’m Tim and I want a 110 F shower. And someone else is going to use a faucet at 1.5 GPM for hand washing at the same time and also at a burning temperature of 110 F. The heater can only give me 3.4 GPM and therefore cant keep up with the 4 GPM demand. However, I bet that Tim would not be doing this.

So now let’s use a more realistic example: A shower at 100 F and hand washing at the same temp. With some simple high school algebra you can calculate that in aggregate 3.27 GPM of HW and 0.72 GPM of cold water will mix to serve both fixtures at 100 F and a total of 4 GPM. Yep, it can keep up. Oh, and by the way there are larger heaters that can handle a larger temp rise at a greater flow rate. Or you can install two heaters in parallel and then double the cataloged capacity (note that if you go this route make sure your installer uses ”a swing check valve” in the piping arrangement). Also, not all heaters cost $1000 [craftsman note: I’m assuming this price Tim refers to was back in ’02, so this argument may not apply]. I have seen them for as low as $250; that is practically the same cost of a tank type. On the other hand if you need to install 2 then of course the price doubles and installation is also more but not likely double the cost.

He also claims that his gas bill increased after he installed the tankless heater. Okay, so what! Tim, can you prove to me that the increase in gas charge was due to the tankless heater? No, you can’t, unless you have a separate meter on your gas supply to your heater. A number of things can affect you gas bill: increased gas billing rate, increase use of gas using appliances, and don’t forget that some appliances such as a gas forced air furnace will use more gas as the outdoor temperature drops. The bottom line is that you cannot simply compare your gas bills between months to determine if your tankless heater is more or less efficient than your old tank type.

Now lets take a step back and stop picking on Tim. We’ll take an engineering perspective at the two types of water heaters.

Tankless heaters by their nature do not have a mass of water that they must keep at a constant temperature all day an all night long but, a tank type does. So it follows that the fuel used to maintain the temperature of the water in the tank when no hot water is being consumed is wasted as compared to a tankless heater. The amount of heating energy needed to raise the temperature of the cold entering water to a useable temperature of 110 or 120 is the same for both types of heaters. It does not matter how the heat energy is added to the water but the laws of heat transfer dictate that if you are raising the temperature of 40 gallons of water (typical tank size) from 55 F to 110 (a 55 temperature rise) you must add 18,354.6 Btus (British thermal Units).

Q=m*cp*ÄT and H2O @ 55 F = 8.343 lb/gal, therefore 40 gallons of water at 55 F weighs 333.72 lbs.

So, 18,354.6 Btus = (333.72 Lbs)*(1)*(55 F)

Q=heat energy

m=mass of fluid

cp=specific heat of fluid

ÄT=temperature rise

The reason that the “burner” on a tankless heater is so much larger and is rated at a much higher output rate than a tank type is that the tankless must create this temperature rise at a much, much faster rate than and tank type heater. For a tankless heater to heat 3.4 GPM of 55 f water to 110 it must the burner must “fire” at 93,500 Btu/hr; however it is not likely that you would need 3.4 GPM at 110 F continuously for and hour, but if you did then a tankless could do that for you. What I’m trying to convey is that yes the burner is large and consumes a lot of fuel quickly but it does not typically run for a long time. Again, a tank type heater would still have to add the same amount of heat to that 3.4 GPM cold of water that is entering the tank to replenish the hot water leaving the tank.

Tankless heaters have another advantage that is related to efficiency but more so related to safety. The American Society of Plumbing Engineers (ASME) recommends that hot water in a storage tank be stored at 160 F to avoid deadly bacteria from growing in the tank, Legionella. Legionella grows well in stagnant water like that in a hot water tank on standby when the temperature is between 95 and 122 F. Obviously a tankless heater is by nature immune to Legionella. An inherent advantage of the tankless heater is that the water is only heated to the temperature that it is needed at 110 to 120 F not to the safety temperature of 160 F. In effect the energy needed to raise the water temperature above 110 or 120 up to 160 F is wasted energy but necessary to ensure safety with this type of heater.

If you had the guts to read this all the way through I commend you. You are definitely hard core. Oh, and Timmy…care to step in the ring? The floor is yours…let the battle live on.

Update: The included body slam image was edited due to Tim Carter “asking” me to pull it down due to copyright infringement.

2nd Update: My sarcastic photo response to Tim Carter’s email was changed in an effort to get the guy to actually respond like he said he would. I must have made him mad. I know the guy has a reputation to keep and he doesn’t want any of my 5 readers to see him in a negative light, but the truth is I just want him to back up his claims. I could care less who ends up being “right.” The truth usually ends up being somewhere in the middle anyways.

Tank vs. Tankless Water Heaters: The War Rages On

Jul 12, 2007 |  by  |  Craftsman Archives  |  Share

tankvstankless Tank vs. Tankless Water Heaters: The War Rages OnAs part of my research for building our Craftsman dream home, I’ve been on a mission to investigate many of the structural and functional pieces that may go into the home. The first of these things was a tankless water heater and all I can say is wow, man. Just when you think you’ve got something figured out you get smacked in the face like a wicked stepchild. I sincerely thought that tankless water heaters were the way to go – supposedly they use less energy compared to the standard storage tank water heater, which is both good for the environment and for my pocketbook. With the average household water usage being close to 65 gallons per day (even higher for families of four or more) and with water heating accounting for up to one-third of home energy costs, clearly a more efficient system, like manufacturers of tankless water heaters claim to produce, would be worth investing in, right? I mean in August of last year the author of the Free Money Finance Blog even took the time to analyze the numbers:

Right from the start, the tankless water heater looks like a great deal. It could cost up to $2,000 at most ($1,000 for the unit and $1,000 for installation), but it saves you $2,000 as well ($100 a year for 20 years). It pays for itself! It seems like a no-brainer at this point. The above numbers reflect the worst-case scenario.

Let’s assume a best-case scenario. Let’s say the tankless water heater costs $1,000 and it’s only $500 to install. And let’s say it saves you $125 per year (the piece does say it saves about $100 or MORE). Finally, let’s assume you get the $300 tax credit on the unit (that’s $300 savings because it’s a credit, not a deduction). In this case, the unit costs $1,200 ($1,000 + $500 – $300) and saves you $2,500 ($125 x 20 years) for a financial GAIN of $1,300. Not bad.

Sounds pretty good right? Makes you want to run out and throw one of those bad boys on your Mastercard or Visa doesn’t it? Well, just hold your horses, Lone Ranger. Because then I read this “controversial” article from Tim Carter at Ask The Builder, which explained why tankless water heaters may not be as efficient as many people think. Now his argument that “some people who buy a tankless water heater end up using more hot water and fuel since the heater never runs out of hot water” doesn’t really apply to me. I mean come on, in a conventional shower (not the 6-headed, spray-every-crack-in -your-body kind) fed by a storage tank water heater, you can take a long ass steaming hot shower until you’ve got skin like Wilford Brimley before the heat runs out. I know. I’ve done it. So if I knew that I could have an endless hot water shower, would I? If I was looking for a way to get a couple of paramedics to haul my naked body away on a stretcher, then maybe. Aside from that argument, Tim does makes an interesting point about the realistic capacity of a tankless heater:

A typical tankless heater with a 165,000 Btu burner can raise the water temperature to 110F and deliver 3.8 gallons per minute of this heated water indefinitely…A code approved typical shower faucet will deliver 2.5 gallons of water per minute. A typical kitchen sink faucet will discharge 2.0 gallons of water per minute. Do the math and you can see that these two common fixtures have exceeded the capacity of the tankless heater.

Also, it’s important to note that the average shower temp for most folks is 115-120F, which is higher than the 110F the tankless heater delivers.

He also provides some credible evidence against the efficiency of tankless heaters:

That month [July] the cost of natural gas in my city [in the Midwest] was 53.4 cents for each 100 cubic feet of gas consumed. My family used 2,400 cubic feet of gas last July. Most of it went to my traditional storage tank water heater, some went to our gas range that was used each day to cook and the remainder went to our gas clothes dryer. I estimate that it cost me approximately 37 cents per day to provide hot water for my family of five and we rarely run out of hot water.

On average, hot water runs in our home approximately 90 minutes each day. 50 minutes of that usage is showers, the rest being cooking and cleaning. If I had a large 165,000 Btu tankless heater at my home, it would have consumed 248 cubic feet of gas each day. Doing the math, I arrive at a cost of $1.32 per day using a whole house tankless heater. Unless I am mistaken, it would cost 3.5 times more money to use this heater in my home.

He’s even had people write in explaining their disappointment with a tankless heater. One lady from Oklahoma said, “Not only have we spent more on the initial costs of the heater and the installation (about $2000), but we have found that since it’s installation we have not saved anything, it has consistently cost us more in natural gas.”

Another guy wrote, “ The bottom line is that we spent $2100 dollars for a tankless water heater that doesn’t conserve energy, takes at least 1 minute to deliver “hot” water, and that has the same warranty as a conventional water heater.”

Puts things in a completely different perspective doesn’t it?

But wait, dammit, there’s more! There’s also this Yanni-without-the-mustache looking guy who did all this hardcore math that showed tankless is the more efficient choice. Are you kidding me? I just want to know if it’s going to save me some money. It really shouldn’t be this complicated.

So it appears the tank vs. tankless battle will go on, and at this point I’m not completely sure what side to join, but between you and me I’m leaning toward The Builder’s point of view. I’d trust a builder over a self-anointed finance guru or a Yanni wannabe any day.

Useful Tankless Water Heater Links: