Hello, everyone. I am new to this so please let me know if i do something dumb.
I have a Kohler Master Shower with 10 heads (2 shower heads 8 body sprays) - yes you read correctly.
I obviously am having problems getting enough hot water. I currently only have a 80 gallon tank.
I have talked to several plumbers and they all have given me a different answer. One mentioned commercial grade water heater (spitfire) and another mentioned a 2 or 3 tankless, and yet a another forum i read about a hybrid (Eternal).
Please help with what you think would be the best. I need about 14 - 16 GPM and i live in central Ohio, so my cold water temp is about 30's to 40's in the winter. And yes, i like really hot showers. So i am thinking about a 70 degree rise at worst case scenario.
thank you for all your help!!
If you have the vertical space below to put in at least a 4-footer (6-footer would be better) 4" drainwater heat exchanger you can get by with half the tankless. The potable side has to be plumbed to both the cold feed to the shower and the cold feed to the HW heater. By raising the temp of the incoming water
A: It mixes in less flow on the hot feed to the shower, and
B: The incoming water to the HW heater is already half-way (or more) there on temperature rise.
There are a handful of vendors (with a history of infighting about patents, labeling etc.), but Natural Resources Canada maintains a list of models that have been 3rd party tested for their efficiency:
At your flow rates the PowerPipe series may be a better choice, since they have less pressure drop than most. They've been attacked by competitors over UL labeling, since they use a heavier-duty copper part than would fall under the guidelines for one of the labeling tests, to be able to braze it together (not a safety or health issue- just thicker copper than the standard presumed would ever be used for house plumbing), but if you have good relationship with the code inspectors it's usually waivered in. (Plan-B would mean using a different vendor's high-flow model, which would still work.) They even qualify for subsidy in WI, OR, and VT. EFI is the US distributor for PowerPipe.
The efficiency numbers are taken at 2gpm flow, but unit that tested at 60% will still be returning ~50% @ 12gpm.
If you installed a heat exchanger first, it would more than double the showering time out of an 80 gallon tank, if that would be enough of an improvement. Or not- it depends on how you use the shower. Most people don't run the side-sprays for the whole shower, so the apparent-capacity improvement would be even better at 4gpm than at 15gpm. (At 2gpm a 5-6' four incher turns a standard 40 gallon tank with a 36K burner into an endless shower situation.) But at the very least it could save you the cost of a third tankless to be able to meet the peak-flow load, and best of all it's more efficient, since it burns no fuel. The cost of the upgraded gas plumbing is going to be significant even going to the first tankless, and hanging 3 (600,000BTU of burner), may be more than the gas company's meter/regulator is designed to handle.
Wow, and we wonder why so much of the world wants to fly jetliners into American buildings. Seems like a trip to a Asian massage parlor would be cheaper and more satisfying.
Dana certainly is right that you need a heat exchanger, [ I hope there are some sort of baffles inside that rig and the outer pipe is soldered to the main pipe, or it looks hokey to me] but mine would be a 50 or 8o gallon tank with the pipe INSIDE the so called grey water [tests have shown most all house drain water to qualify as black] That tank would also radiate heat into the house when you are not being assualted by the firehoses.
With a good lint trap, you could run the drain water thru a nice diesel truck radiator and blow the hot air into the house. If you and the wife showered daily, you could turn off the furnace.
Then your rating as a enviro-destroying-terrorist falls from a 10 to a 8. Maybe someone fracked the shale under your house and your gas is free, and your running on rainwater. Then you get a 1.
Buy a jetted bathtub and dont drain it until the water is cold. Thats your FREE heat exchanger.
I just wonder how my grandparents lived 90 years and only turned the water heater on for a Saturday? And smoked a big cigar with a few shots of Brandy while soaking.
An aunt in Slovakia with packed dirt floors with a nice layer of linseed oil made over 100 years,
and her only hot water came off the wood stove in a pot. Her Kohler shower was a wet rag.
Last edited by ballvalve; 01-27-2012 at 01:19 PM.
The percentage of 140 degree water with a mix of 79 degree cold water to arrive at a showering temp of 104......is close to 42% hot water at 140.
Now the percentage of 140 degree water with a mix of 50 degree cold water to arrive at a showering temp of 104 is close to 61%
Thats a 19% difference and thats not enough to double the showering time. Not near.
Hackney: As if the burner on the tank never fires?
Don't take the temperature numbers in that picture too literally- it's a piece of marketing hype from one of the smaller vendors, but I posted it for clarity of how the output needs to be plumbed. They're a bit optimistic on the drainwater temp if the shower head output is actually 40C, the drain will be a few degrees less, but the concept is clear. The actual temp out of potable side of the HX depends on the flow and the size- the taller-fatter ones will actually exceed 80F at 2.5gpm balance-flow configurations.
For reference, the 4" x 4' in my basement delivers a delta-T of ~30F during the cold water months at whatever uncalibrated gusher-head flow my shower is running, but it's probably more than 2.5, less than 3.5gpm, and I can shower 24/365 without the boiler modulating any higher than ~55-60KBTU/hr. (YMMV) and that's even with sub-40F incoming water. Since it's not running as a priority zone, it'll sneak up to ~70KBTU/hr output with all zones calling for heat while somebody is in the shower, and I have the hydro-air zone set up to kick off when the water temp drops to ~110F to be sure that the shower literally never runs cold (all heat is pulling from the same buffer tank, single temp, but the DHW is isolated with an internal HX in the buffer.)
The BTU input rate of the burner on an 80 gallon tank is pretty substantial (but unstated.) If he's not pulling the ungodly 15gpm continuously, burner-on counts for a lot. In third party Canadian testing at 2.5 gpm flows, when plumbed as in the above diagram, it takes about an hour for the shower head temp to drop below 37C (body temperature) with standard-burner 40 gallon gas-fired tanks with ~8C incoming water, and goes literally forever with higher BTU burners. (If you want test data much of it is available online with a google search, and not too hard to find. googling on "drainwater" in combination with "NRCAN" gets you a bunch of the very-abbreviated overviews, and some of the characterization test descriptions.)
With ~2x the tank ~2x the burner, assuming the sidesprays aren't running a 100% duty cycle so maybe it's only 4x the average flow (rather than ~8x) it won't run for the hour with only an 75-80K burner behind it, but, with the burner firing it'll still go a LOT further that it can without the BTU feedback of the HX. If it's ~4-5 gpm for most of the showering period, but 15-16gpm for a few minutes at the end, that's totally tank-able with the HX (and totally NOT without it.) At 8x the flow continuously it needs more burner, but the price and performance of the HX is still better than adding a third tankless.
Ballvalve: The center pipe is a smooth bore copper drain, and it counts on a vertical orientation and the surface tension of the greywater to spread as a thin film clinging to the interior of the pipe, which is does. So called "gravity film" heat exchangers like this have been around for about 30 years now, and they've since been improved both performance & anticipated longevity (~30-50 years before hitting only 75% of day-1 efficiency.)
At current gas prices most people won't have them long enough to pay off, but with gusher showers like that the payback is pretty quick- like the first time your wife goes into the shower shortly after you, and doesn't come back screaming. (Have you priced divorce lawyers? :-) )
At 15 gpm 43% of that being hot equals 6.45 gpm a minute being pulled out of the 80 gal water heater. Every 12 minutes the water heaters water will totally exchange.........the burner firing isn't gonna make a crap in a typical 80 gal gas.
Last edited by Hackney plumbing; 01-27-2012 at 04:53 PM.
For maximum efficiency at the highest flow rate, you may need two run with a manifold in parallel. They can provide them with up to 4 units, if I read their info correctly. One pipe is pretty much limited to a max of 10gpm. At your max flow rates, you're more in the commercial range than residential.
Important note - I'm not a pro
Retired Defense Industry Engineer
With the drainwater heat exchanger a balanced flow configuration the antiscald issues with the mixer only sees the pressure differential across the hot water heater, which is much higher with a tankless than a tank.
In some installations ONLY the HW heater is fed by the DWHX, but with the colder cold-side mix water and lower potable side flow as a system it takes a 15-20% hit in performance. In a balanced flow situation with higher temp mixwater the hot-water side flow is substantially lower, and with the input side to the water heater already halfway up to temp (or more) the BTU-input point where the burner simply keeps up is much reduced.
High flow rates are an issue (for both a tankless HX and a drainwater HX), which is why I suggested PowerPipe over some of the competition, since it has the lowest impedance to the potable water. Almost all of the larger DWHX units use 3/4" connections, but on the PowerPipe that immediately with a manifold into 4 flattened sections of higher cross section/lower impedance than 3/4" plumbing:
The head presented by a 6' PowerPipe is less than that of a tankless, and may be less than 2 tanklesses plumbed in parallel.
The manifold of the PowerPipe is thicker material than the range covered by the ASTM B 88 spelled out in plumbing codes, so they've tested to ASTM B 75 instead, but since it can't be marked with the stripe per code some inspectors have made an issue of it, but variances are routinely allowed when the issue is properly understood.
I like the drainwater exchanger for what it is,I really do but I dont think you could get by with 1/2 the tankless if he used it in this situation.
What does an entry level exchanger cost and what does the largest model cost? Whats involved in maintaining it?
Last edited by Hackney plumbing; 01-30-2012 at 06:53 PM.
at 15gpm, you'd need more than one exchanger, if I read the spec sheet correctly as a single one is limited to about 10gpm max flow. Then, ensuring you get somewhat even flow through the pair in parallel (they make a manifold for up to 4) probably works iwth their stuff, but I'd want to talk to them first.
Important note - I'm not a pro
Retired Defense Industry Engineer
At 15gpm the return efficiency is going to fall off, but my question to the O.P. was whether he needed the 15gpm continuously or whether it was a 4-5gpm shower with a few minutes of 15gpm at the end, in which case this would work. I've already stated in a prior post that it's totally NOT a total solution for a 15gpm continuous shower, even if it would pay for itself in short years in any high-flow shower, any fuel.
At full-retail from the Orange Box Store in Canada you can spend up to a grand or even $1.7KCDN if you have room for a 10 footer. In Canada you can even buy them mail-order or have them installed through Sears. For middle of the road versions from the US distributor for PowerPipe, EFI a 4x4 runs ~$600USD, shipped. (You can open an account with a credit card over the phone, and they'll ship them onesie-twosie from their Wisconsin facility. EcoInnovation sells direct to US customers for ~$500-600 shipped, but not all models show up on the NRCAN third-party tested list of units eligible for grants/rebates. (They claim their newer models are higher efficiency- but they're not on the current list.)
There are many ~$500 options out there with 40%+ efficiency @ 2.5gpm (and higher efficiency at lower flow). At 20-30 minutes of showering at 2gpm/day a family heating their hot water with electricity/propane/oil will see a real ROI. But 10 minutes/day at current natural gas pricing, fuggedaboudit.
There is no maintenance required for these units- temps are low enough that liming/scaling on the potable side just doesn't happen (although in the extreme hard water cases where you'd be deliming your tankless 2x/year or more often I suppose anything is possible.) On the greywater side it's a smooth bore copper drainpipe which stays pretty clean inherently, since it's being rinsed with mild detergents with every shower. I haven't seen third party longevity testing, but some private company testing shows that performance can deteriorate to ~75% of day 1 efficiency over something like 3-5 decades in a home shower use. In car wash and commercial laundry applications even with massive volume use they hang in there quite well.
Jim- which spec sheet shows a 10gpm limit? IIRC the absolute flow limit on the PowerPipe is essentially the head of 3/4" copper pipe at about ~2-3x the length of the HX, but the efficiency falls off with flow, losing on the order of 7% overall efficiency for every doubling of flow. Something rated at 60% @ 2.5gpm only delivers ~53% @ 5gpm, but still delivers 46% @ 10gpm, etc. On other vendors' slinky-wrap designs the head presented on the potable side is a serious limitation to high flow rates. The curves from another vendor's (older) product line look like this.
If you feel the need for a bed-time read on the characteristics of these beasts, try this.
Several US states & utilities (OR, WI, VT, parts of NY, & CT) offer rebate type incentives for models above some minimum efficiency based on NRCAN third party testing, but it's more common in Canada (which is why most, but not all vendors are from north of the border.) It's a tiny industry with a fair amount of back-biting and infighting over patents etc., (I'll leave that up to the courts to figure out the merits, but if you research it online it's easy to find a lot of claims & counterclaims.) For lack of better information the NRCAN rebate-eligible models list is probably the best for comparing apples-to-apples on efficiency.
I read that 10gpm figure on one of their pages...not sure if it was advertising, engineering, or installation, but it was on the powerpipe design and their website. While the pipe itself can easily handle much more drainage than that, if you want to obtain good results, when it exceeds 10gpm, you need more than one path and thus the manifold(s).
Important note - I'm not a pro
Retired Defense Industry Engineer
To be sure the efficiency of the heat exchanger drops off with higher flow rates, but even at 15gpm it's still going to be well over half whatever the 2.5gpm rated number is.
Getting drain manifolds to balance the drain flow between multiple heat exchangers reasonably may take a bit of on-site engineering get it to work correctly, but it's clearly possible, since it's done at bigger commercial installations. Even a single 6-footer could reduce the number of tankless units from 3 down to 2, and put less stress on the tankless units:
A 199KBTU burner condensing tankless units are rated for ~4.2gpm @ 75F rise, 9.8gpm max @ 35F rise. At max fire don't expect more than about 90% efficiency out of it, which means only 180KBTU/hr per unit getting into the water, or 360K/hr total. A flow of 15gpm is 7500lbs/hr, so the max delta-T you can expect is (360,000/7500=) 48F. With a 105F shower it means it fails at 57F incoming water temps- fine for the summer, but for the rest of the year... For 35F water you're looking at a delta-T of 70F. 70F x 7500lbs/hr = 525,000BTU/hr, which means you'd just squeak it in with three condensing 199K tankless. If in the tankless actually makes it to 95% efficiency or higher it doesn't change the math much- you'll still need three and the margins would be slim.
But instead of a third tankless, at 15gpm flow a single 4x6 PowerPipe (rated ~63% @ 2.5gpm) would be returning over 40% of that 525KBTU/hr. That's over 210KBTU/hr, which is MORE heat than the output of a third tankless, giving it better margin on the BTU front, and lowering the average flow through pair of tankless units, reducing stress on the flow sensors & heat exchangers. And it's cutting the fuel burned by about 40%. DWHX is cheaper to buy, install, and operate than a third tankless.
BTW: I see that you can now order PowerPipe units online (at retail pricing), directly from the manufacturer, shipped to the US & Canada.
For the record (lest I come off as a sales-droid's shill) I have no commercial or other interest in that company or any other part of that industry, nor do I intend to in the future. But they do actually work, and this is an application where it's the most cost-effective way forward.