Multiple Head Shower

[Bivik]

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!!

[Hackney plumbing]

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!!

Tankless and enough of them to supply the demand.

[Dana]

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:

http://oee.nrcan.gc.ca/residential/p...retrofit/13302

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.

[ballvalve]

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.

[Hackney plumbing]

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:

http://oee.nrcan.gc.ca/residential/p...retrofit/13302

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.

With a water heater setting of 140 your illustration shows that being piped to the hot side of the faucet and 79 degree tempered water to the cold side of the valve after it goes through your heat exchanger. The oulet temp is shown at 104 degrees.

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.

[Dana]

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? :-) )

[Hackney plumbing]

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? :-) )

The burner fires but the tank being fed by 50 degree water because its not tempered by your heat exchanger and to make it worse the guy blasting a high volume of water. If he connected your system he wouldn't get that high flow anymore......I suspect the inlet and outlet of the heat exchanger is 1/2". His valve will be pressure balanced so with the pressure drop through the heat exchanger will be copied on the hot side of the valve reducing flow.

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.

[jadnashua]

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.

[Dana]

The burner fires but the tank being fed by 50 degree water because its not tempered by your heat exchanger and to make it worse the guy blasting a high volume of water. If he connected your system he wouldn't get that high flow anymore......I suspect the inlet and outlet of the heat exchanger is 1/2". His valve will be pressure balanced so with the pressure drop through the heat exchanger will be copied on the hot side of the valve reducing flow.

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.

No, the HW heater is being fed 75-85F water (if you get a 4" x 5' or larger ) straight out of the drainwater heat exchanger (as is the cold water feed to the shower.) The output of the potable side flow of HX is identical to that of the drainwater flow. Maybe that first diagram was too confusing. This makes it dead-obvious:



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.