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Hot Water Runs Out

Hi,

I recently had my boiler and indirect water heater replaced.

The old boiler was a Weil-McLain WGO-6 with 212 MBH and the old indirect water heater was a 41 gallon Amtrol BoilerMate.

The new boiler is a Utica Trifire TRB5100 with 123 MBH and the new indirect water heater is a 45 gallon Superstor.

The other day we had 2 showers running at the same time and the hot water ran out after 8 minutes. We never ran out of hot water with the old equipment.

I reported this issue to the installer and they came to turn on DHW zone priority but that still hasn’t solved the problem. They are coming back to troubleshoot further and I was hoping to educate myself a bit before they do so I can better evaluate any potential solutions they recommend.

What are the first things you would check if you were diagnosing an issue like this?

Here is some more information about the system.

The system has one zone piped to an air handler located next to the boiler, one zone piped to the water heater also located next to the boiler, and one zone piped to an 18’ fin tube baseboard at the opposite end of the house that we don’t normally use.

The installer replaced all piping from the boiler to the air handler and water heater. There’s 1” piping for the water heater with a Taco 0015 circulator for the zone. The boiler high limit is set to 180 and the water heater aquastat is set to 130.

Here are some pictures of the equipment.

Thanks in advance!




«1

Comments

  • mattmia2
    mattmia2 Member Posts: 7,207
    Your indirect is probably too small. Your old boiler could make about 6.6 gallons per minute going from 40f to 100f. your new boiler can make about 3.3 gal per minute. It probably worked ok in summer with higher incoming water temps, but now the incoming water is colder. Since the boiler is probably sized to the load of the house now you need to store more energy in the indirect tank to cover your dhw load.
  • JakeCK
    JakeCK Member Posts: 1,130
    A potential solution is a drain water heat recovery unit if you have enough vertical distance on you main stack below the showers. You're going to spend more on a second tank or replacing your current new tank with a larger one than you would for one of these heat exchangers and the exchanger would at least have a ROI.

    https://www.energy.gov/energysaver/drain-water-heat-recovery
    Larry WeingartenHot_water_fan
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,149
    @spd1980

    I don't agree with the above posts. I don't see how you could run out in 8 min.

    There are several things to check.

    1. The 1" pipe to the indirect is slightly undersized 1 1/4" would be better. HTP want's the coil to have 10gpm from the boiler. But the run is short so I don't think that's the main issue.

    2. HTP wants a flow of 10 gpm and the coils resistance is 7.9 feet of head. The taco 0015 @ 10 gpm will produce 9' of head.

    So what is left for the resistance of the pipe, fittings and valves is 1.1 feet of head (9-7.9)

    I calculated your pipe and fittings to about 5' of head. so your total head coil, pipe and fittings is at least 12.9' call it 13. and I didn't count the boiler and other fittings.

    At 13' of head the taco pump will do about 5.5 gpm not the 10 gpm you need.

    What I would do is put a digital thermometer on the supply and return pipes at the indirect to measure the boiler supply and return.

    You want a 20 degree TD (less is better) between the supply and return with the boiler running and drawing hot water out of the indirect.

    You could also up the boiler temp to 190 high limit but you shouldn't need to.

    Also the shower heads check the GPM you are drawing. Use a bucket. Catch the water for 30 seconds x2 that and you will have your gpm.
    DerheatmeisterSTEVEusaPA
  • mattmia2
    mattmia2 Member Posts: 7,207
    edited December 2021
    I could see 2 showers at about 3 gpm each doing it in 8 minutes, especially if the setpoint of the tank is lower. 6 gpm * 8 minutes is 48 gallons. That isn't all coming from the tank, but it is enough to stir up the stagnation and bring the colder water entering and being partially heated at the bottom up to the outlet near the top. I can do it with my ssu40 and one shower in under 15 minutes if i'm not careful about limiting the flow.
  • PC7060
    PC7060 Member Posts: 912
    3GPM seems too high for modern controls and shower heads. Most are 1.6GPM which should be satisfied by @mattmia2 projected 3.3GPM supply. 
    kcopp
  • kcopp
    kcopp Member Posts: 4,092
    Simple way to start is to put a mixing valve on the Superstor. Raise the water temp to 140F and mix down to 120ish. By some codes this is now required.
    I also agree 3.3 gpm is huge for a showerhead.
    DerheatmeisterSuperTech
  • PC7060
    PC7060 Member Posts: 912
    kcopp said:
    Simple way to start is to put a mixing valve on the Superstor. Raise the water temp to 140F and mix down to 120ish. By some codes this is now required. I also agree 3.3 gpm is huge for a showerhead.
    Good idea, @kcopp.  I did same thing using a Caleffi mixer set to 115F output.
  • spd1980
    spd1980 Member Posts: 47
    mattmia2 said:
    Your indirect is probably too small. Your old boiler could make about 6.6 gallons per minute going from 40f to 100f. your new boiler can make about 3.3 gal per minute. It probably worked ok in summer with higher incoming water temps, but now the incoming water is colder. Since the boiler is probably sized to the load of the house now you need to store more energy in the indirect tank to cover your dhw load.
    Thanks. I had wondered if it was due to the new boiler being smaller. The boiler is 123 MBH and the water heater lists a minimum of 141MBH to meet the first hour rating.
  • spd1980
    spd1980 Member Posts: 47
    JakeCK said:
    A potential solution is a drain water heat recovery unit if you have enough vertical distance on you main stack below the showers. You're going to spend more on a second tank or replacing your current new tank with a larger one than you would for one of these heat exchangers and the exchanger would at least have a ROI.

    https://www.energy.gov/energysaver/drain-water-heat-recovery
    Thanks. This is something I did not know about and it sounds like a good option if the installer recommends costly solutions. 
  • spd1980
    spd1980 Member Posts: 47
    @spd1980 I don't agree with the above posts. I don't see how you could run out in 8 min. There are several things to check. 1. The 1" pipe to the indirect is slightly undersized 1 1/4" would be better. HTP want's the coil to have 10gpm from the boiler. But the run is short so I don't think that's the main issue. 2. HTP wants a flow of 10 gpm and the coils resistance is 7.9 feet of head. The taco 0015 @ 10 gpm will produce 9' of head. So what is left for the resistance of the pipe, fittings and valves is 1.1 feet of head (9-7.9) I calculated your pipe and fittings to about 5' of head. so your total head coil, pipe and fittings is at least 12.9' call it 13. and I didn't count the boiler and other fittings. At 13' of head the taco pump will do about 5.5 gpm not the 10 gpm you need. What I would do is put a digital thermometer on the supply and return pipes at the indirect to measure the boiler supply and return. You want a 20 degree TD (less is better) between the supply and return with the boiler running and drawing hot water out of the indirect. You could also up the boiler temp to 190 high limit but you shouldn't need to. Also the shower heads check the GPM you are drawing. Use a bucket. Catch the water for 30 seconds x2 that and you will have your gpm.
    Thanks. I wondered about the flow rates and supply/return temps but didn’t really know how to gauge whether they could be an issue.

    I measured the flow rate of both showers and one is 3 GPM and the other is 2.5 GPM for a total of 5.5 GPM.

    Next, I turned both showers on all the way to hot and measured a supply temp of 161 and return temp of 139 when the boiler had just hit the 180 high limit. The measurements were taken at the water heater and the DHW zone was the only zone calling for heat at the time. When the boiler kicked back on at 170 (the temp still fell to 165 before rising again) I measured a supply temp of 140 and return temp of 119.
  • spd1980
    spd1980 Member Posts: 47
    PC7060 said:
    3GPM seems too high for modern controls and shower heads. Most are 1.6GPM which should be satisfied by @mattmia2 projected 3.3GPM supply. 
    I measured the GPM with a bucket and found 3 GPM and 2.5 GPM for a total of 5.5 GPM with both showers running. 
  • spd1980
    spd1980 Member Posts: 47
    kcopp said:
    Simple way to start is to put a mixing valve on the Superstor. Raise the water temp to 140F and mix down to 120ish. By some codes this is now required. I also agree 3.3 gpm is huge for a showerhead.
    Thanks. That sounds like an interesting option. I do wonder if 120 will feel warm enough for my wife. We initially had the heater temp set to 120 and she commented it didn’t feel as warm so that’s when I set the heater temp to 130. Interestingly, my old BoilerMate temperature display read 120 but the water felt hotter at that temp then it did for the new water heater.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,149
    @spd1980

    As you can see the Taco circ is just about boarder line as your close to the 20 degree split on the boiler water.

    Some things that will help:

    Get the high limit to 190.

    Reduce the differential on the high limit (if you can) so it will keep up

    5.5gpm is a big load you could change shower heads or put in flow restrictors

    Run the tank hotter and mix it down to 120 as others have mentioned

    Is that Taco a 3 speed pump and is it on high speed?

    you would do better with a larger pump but I am more concerned about the temp drop between the boiler and the tank if your readings are accurate.



    What I am finding odd is that when the boiler is off at 180 limit you only have 161 at the super store? Why is that?

    When the boiler came back on at 170 you only had 140 at the tank?

    Maybe your thermometer is off?

  • neilc
    neilc Member Posts: 2,088
    any chance the domestic heating loop is drawing thru one of the other heating loops, and not off the top of the boiler?

    if on a domestic only call, do either of the other returns get boiler hot?
    do all the circs have flowchecks?
    known to beat dead horses
  • spd1980
    spd1980 Member Posts: 47
    @spd1980 As you can see the Taco circ is just about boarder line as your close to the 20 degree split on the boiler water. Some things that will help: Get the high limit to 190. Reduce the differential on the high limit (if you can) so it will keep up 5.5gpm is a big load you could change shower heads or put in flow restrictors Run the tank hotter and mix it down to 120 as others have mentioned Is that Taco a 3 speed pump and is it on high speed? you would do better with a larger pump but I am more concerned about the temp drop between the boiler and the tank if your readings are accurate. What I am finding odd is that when the boiler is off at 180 limit you only have 161 at the super store? Why is that? When the boiler came back on at 170 you only had 140 at the tank? Maybe your thermometer is off?
    Thanks. I had wondered about setting the high limit to 190 as according to the manual that is what the factory setting was, though maybe that’s just a common default. 

    I can’t adjust the differential. It’s automatic and set to 10 degrees with economy mode settings off, which they are.

    The circulator is set to high currently.

    It’s possible I might not be getting an accurate reading. I only have an instant read food thermometer. I tried to make contact with the pipe in a way that reported the highest temperature and confirmed the reading remained steady. I’ll ask the installer to take a more accurate measurement.
  • neilc
    neilc Member Posts: 2,088
    edited December 2021
    paint, or wrap with electrical tape, a flat black is best, to get a more accurate laser reading
    withdrawn, thought I saw a laser in a picture, wrong thread
    known to beat dead horses
  • PC7060
    PC7060 Member Posts: 912
    edited December 2021
    neilc said:
    paint, or wrap with electrical tape, a flat black is best, to get a more accurate laser reading withdrawn, thought I saw a laser in a picture, wrong thread
    I was wondering same thing. Copper piping are difficult to get reading off using IR handheld unit. Too much reflection. 
  • neilc
    neilc Member Posts: 2,088
    if that's a contact thermometer,
    try wrapping a leather work glove, or shop rag or towel, to hold and insulate the probe at the contact points,
    caution, hot !
    known to beat dead horses
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,785
    Hi @spd1980 , I don't think anyone has mentioned the idea of putting on low flow showerheads. They come in 1.5 gpm flow, which would probably solve your problem, inexpensively. I actually use the one made by Delta and like it.

    Yours, Larry
    PC7060
  • mattmia2
    mattmia2 Member Posts: 7,207
    spd1980 said:


    kcopp said:

    Simple way to start is to put a mixing valve on the Superstor. Raise the water temp to 140F and mix down to 120ish. By some codes this is now required.
    I also agree 3.3 gpm is huge for a showerhead.

    Thanks. That sounds like an interesting option. I do wonder if 120 will feel warm enough for my wife. We initially had the heater temp set to 120 and she commented it didn’t feel as warm so that’s when I set the heater temp to 130. Interestingly, my old BoilerMate temperature display read 120 but the water felt hotter at that temp then it did for the new water heater.

    I suspect the shower control has a stop in it that sets the max amount of hot you can mix in to satisfy the scald protection code requirement. That stop probably set for a higher dhw temp. You could adjust that stop if you set the dhw for 120 but that won't solve your problem of not making enough hot water.
  • Jamie Hall
    Jamie Hall Member Posts: 20,500
    "Thanks. I had wondered if it was due to the new boiler being smaller. The boiler is 123 MBH and the water heater lists a minimum of 141MBH to meet the first hour rating."

    And your two showerheads are at 5.5 gpm?

    Mother nature is mean. Your two showerheads together would need almost 200,000 BTUh from the burner to keep up. You don't have that, and the Superstor couldn't take it anyway. So you will draw hot water from the Superstor, OK, but the boiler can't replace it as fast as you use it. The showers will get cold or at least cool once the Superstor is exhausted -- which will take a bit more that 8 minutes.

    No amount of juggling with the settings of this and that or the flow rates from the boiler or... hope... is going to change that.

    Sorry.

    Solutions. Low flow shower heads. Run one shower at a time (the 141,000 BTUh will handle up to about 4 gpm). The existing boiler will handle about 3.5 gpm continuously. Get more storage (that's why the big electric and hybrid water heaters -- which have horrible recovery rates -- work at all)(which would at least give you more time before getting chilled).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 7,207
    The thing is it doesn't run out in 8 minutes but it gets cooler so it feels like it has run out.
  • Jon_blaney
    Jon_blaney Member Posts: 294
    While they are there, have them fix the pressure tank. It should hang down and be supported. When it fails, the current arangement will cause a piping failure.
    SuperTech
  • spd1980
    spd1980 Member Posts: 47
    neilc said:
    if that's a contact thermometer, try wrapping a leather work glove, or shop rag or towel, to hold and insulate the probe at the contact points, caution, hot !
    I tried that and still read about 20 degrees lower than the boiler when measuring at the water heater. I also tried measuring the boiler supply temp right before the DHW circulator and read about 10 degrees less than the boiler. I probably just need a more accurate way to measure the temperature.


  • spd1980
    spd1980 Member Posts: 47
    neilc said:
    any chance the domestic heating loop is drawing thru one of the other heating loops, and not off the top of the boiler? if on a domestic only call, do either of the other returns get boiler hot? do all the circs have flowchecks?
    All circs have flow checks and the supply and return pipes are cold for the non-DHW zones. 
  • spd1980
    spd1980 Member Posts: 47
    Hi @spd1980 , I don't think anyone has mentioned the idea of putting on low flow showerheads. They come in 1.5 gpm flow, which would probably solve your problem, inexpensively. I actually use the one made by Delta and like it. Yours, Larry
    Thanks glad to know that’s an option.
  • spd1980
    spd1980 Member Posts: 47
    "Thanks. I had wondered if it was due to the new boiler being smaller. The boiler is 123 MBH and the water heater lists a minimum of 141MBH to meet the first hour rating." And your two showerheads are at 5.5 gpm? Mother nature is mean. Your two showerheads together would need almost 200,000 BTUh from the burner to keep up. You don't have that, and the Superstor couldn't take it anyway. So you will draw hot water from the Superstor, OK, but the boiler can't replace it as fast as you use it. The showers will get cold or at least cool once the Superstor is exhausted -- which will take a bit more that 8 minutes. No amount of juggling with the settings of this and that or the flow rates from the boiler or... hope... is going to change that. Sorry. Solutions. Low flow shower heads. Run one shower at a time (the 141,000 BTUh will handle up to about 4 gpm). The existing boiler will handle about 3.5 gpm continuously. Get more storage (that's why the big electric and hybrid water heaters -- which have horrible recovery rates -- work at all)(which would at least give you more time before getting chilled).
    Thanks. I guess there was a reason my old boiler had so much heating capacity, it was sized for the hot water instead of the heat.

    I feel like my installer did a poor job of taking the hot water into account when sizing the boiler. When he sent me the quote for this boiler, I asked if a bigger one was necessary since other companies recommended something bigger, and he sent me an updated quote for the next model up at 160 MBH and that was the model I was planning to get.

    On the day of the install he showed up with the smaller model boiler because that was all he could get from the distributor, and it sounded like he knew that for a few weeks before the install date, and he reassured me that it would be more than sufficient, and if not we could always change the burner nozzle to up fire it or even switch the boiler out. 

    I still haven’t paid the last 50% of the invoice yet so if anything now is the time to have the installer make things right. I understand mistakes happen but I also want things to work as they did and as they were expected to and it feels like a bait and switch due to giving me the smaller boiler even if the next model up wouldn’t have completely solved the problem.

    It feels like the best solution is a bigger boiler or more hot water storage but that would probably be at a big cost to the installer and I’m sure they most likely would want to avoid doing that.

    What would be some of the most reasonable ways for the installer to make things right in this situation?

    I would like to avoid band aid solutions if possible. I know my wife will complain if the shower water pressure changes at all, or if the water feels too cool with a mixing valve, or if we can’t wash a load of laundry and shower at the same time.

    Sorry for the long post, it’s just that this is an expensive project so I want to feel satisfied with it.
  • spd1980
    spd1980 Member Posts: 47
    While they are there, have them fix the pressure tank. It should hang down and be supported. When it fails, the current arangement will cause a piping failure.
    Thanks for the suggestion.

    I assume they should support both expansion tanks?

    Also, what is an effective way of asking them to do something like this and actually getting them to do it? As a fairly recent homeowner I’m inexperienced in managing home improvement projects and it seems like most people want to take the easy way out and claim everything is fine just so they don’t have to do anything.
  • JakeCK
    JakeCK Member Posts: 1,130
    Again, get a drain recovery unit since it has already been noted your gpm is too high for the tank you have. It can almost double your available hot water by raising the supply water temp substantially. Many of these old timers don't like or trust new fangled things for some reason even though it uses a well established and understood technology. eg a copper heat exchanger. Getting a low flow head will solve the problem too but your wife might notice that as well. 

    Happy wife, happy life. Spending a few benjamin's to keep that in balance is money well spent.

    Also sizing to the heating load wasn't really a bad idea. That is going to save you money in the long run. The only other way to have an oversized boiler and still have it run efficiently is by using a large buffer tank. 
    Hot_water_fan
  • mattmia2
    mattmia2 Member Posts: 7,207
    JakeCK said:

    Again, get a drain recovery unit since it has already been noted your gpm is too high for the tank you have. It can almost double your available hot water by raising the supply water temp substantially. Many of these old timers don't like or trust new fangled things for some reason even though it uses a well established and understood technology. eg a copper heat exchanger.

    I'm not seeing much heat moving through a hx with a square foot or so of effective transfer area and a delta t of 30 f or so.

    SuperTech
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,149
    In the first place NO one sizes a boiler for the DHW load unless it is a commercial job or you have a large load like a hot tub or if it was spelled out prior to the install. A couple of bathrooms ....learn to live with it...the shower heads are too large.

    I had mentioned the shower heads in my first post that should be the first step to managing the problem.

    The pump is doing about 55% of the gpm Superstore wants. This is causing a wider temperature drop through the coil about 21 degrees if measured right. More flow through the coil means more of the coil runs at a higher temperature.

    I have no idea what Superstore wants for a TD on the boiler water, only that they want 10 gpm

    The boiler temp should be increased.

    The pump is slightly undersized partially due to the 1" pipe being used where it should have been 1 1/4" for a 10 gpm flow
    PC7060
  • neilc
    neilc Member Posts: 2,088
    I know someone else mentioned it, but,
    set the storage tank higher, 140~150(?),
    then add a mix valve and temper the water back down to 120~ well 120,

    low flow head for the subordinate showers
    known to beat dead horses
    SuperTech
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,785
    Hi, Just to get into the weeds a bit on some different aspects of this. First, GPM of the showerheads... Not all of the water coming from the showerhead is hot. Normally the percentage of hot water coming from the showerhead is 50% to 70% of the total, so even with your 3 GPM head, it's using at most 2.1 GPM of hot water. This suggests that the system REALLY isn't keeping up with demand. Next, low flow showerheads can actually feel better than high flow. The better heads produce large water droplets, which hold heat better than smaller droplets and the lower flow reduces friction losses in the piping, so you get more pressure/faster moving and bigger/hotter droplets hitting you. This particularly matters because the water cools substantially traveling from the showerhead to the bather. Men have less of a problem with this because we're generally taller. Just that little difference in height can give women noticeably cooler water. To test this, feel the temp of the water right at the showerhead and again three or four feet away, with the same hand. You'll notice the difference. Here's an image of the Delta showerhead I mentioned. It's a quick, inexpensive fix that you will probably want to keep.

    Next is the shower heat exchanger. Sized for best performance, you'll see that a shower heat exchanger can capture 60% of the otherwise lost heat, basically doubling the showering time. Here's a link to information: https://renewability.com/reference/ Of course, you'll need a place to install it vertically. I installed one in my home and plumbed it so that it feeds warmed water to the cold side of the shower. This is simple plumbing, though I usually need to adjust the temperature down or the shower gets too hot.

    Third is that you can only expect to get 70% to 75% of the volume of your water tank as undiluted hot water. So, at best, you can get 33.75 gallons of hot water from your present tank, plus how much water gets heated as you shower.

    Sorry for the long post, but hope it helps!

    Yours, Larry
  • spd1980
    spd1980 Member Posts: 47
    JakeCK said:
    Again, get a drain recovery unit since it has already been noted your gpm is too high for the tank you have. It can almost double your available hot water by raising the supply water temp substantially. Many of these old timers don't like or trust new fangled things for some reason even though it uses a well established and understood technology. eg a copper heat exchanger. Getting a low flow head will solve the problem too but your wife might notice that as well. 

    Happy wife, happy life. Spending a few benjamin's to keep that in balance is money well spent.

    Also sizing to the heating load wasn't really a bad idea. That is going to save you money in the long run. The only other way to have an oversized boiler and still have it run efficiently is by using a large buffer tank. 
    Saving money on fuel is one nice benefit so maybe I can play that up to make the situation more palatable.

    So I wonder if I should plan to turn the high limit to 190, change the shower heads, turn the aquastat to 140, and add a mixing valve for now then if that still isn’t enough add a drain recovery unit.
  • spd1980
    spd1980 Member Posts: 47
    In the first place NO one sizes a boiler for the DHW load unless it is a commercial job or you have a large load like a hot tub or if it was spelled out prior to the install. A couple of bathrooms ....learn to live with it...the shower heads are too large. I had mentioned the shower heads in my first post that should be the first step to managing the problem. The pump is doing about 55% of the gpm Superstore wants. This is causing a wider temperature drop through the coil about 21 degrees if measured right. More flow through the coil means more of the coil runs at a higher temperature. I have no idea what Superstore wants for a TD on the boiler water, only that they want 10 gpm The boiler temp should be increased. The pump is slightly undersized partially due to the 1" pipe being used where it should have been 1 1/4" for a 10 gpm flow
    Thanks again. After taking everything into consideration it does seem like raising the high limit, changing the shower heads, and adding a mixing valve would be a good first step.

    Would it also be worthwhile to push the installer to use a larger circulator? I assume they wouldn’t want to re-pipe with 1 1/4” pipe but a circulator shouldn’t be too difficult to swap out if it will make a difference. 
  • spd1980
    spd1980 Member Posts: 47
    neilc said:
    I know someone else mentioned it, but, set the storage tank higher, 140~150(?), then add a mix valve and temper the water back down to 120~ well 120, low flow head for the subordinate showers
    Yeah thanks it does sound like those are the best options to start with. 
    MikeAmann
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,149
    Yeah any storage tank they used to say that 80% of the water is hot. Of course this varies with the incoming water temp. Worse in the winter and better in the summer.

    But @Larry Weingarten #s are probably more accurate
  • JakeCK
    JakeCK Member Posts: 1,130
    edited December 2021
    mattmia2 said:
    Again, get a drain recovery unit since it has already been noted your gpm is too high for the tank you have. It can almost double your available hot water by raising the supply water temp substantially. Many of these old timers don't like or trust new fangled things for some reason even though it uses a well established and understood technology. eg a copper heat exchanger.
    I'm not seeing much heat moving through a hx with a square foot or so of effective transfer area and a delta t of 30 f or so.
    A delta of 30f? I think you need to recheck your math. Suppose you are taking a steaming hot shower as hot as it can put out(My wife does it, I can't, she can.) with the water going down the drain ~100f and you have a supply water temperature of 35-40. Southern states might not see such a low water temp but I do! Whats the delta? Also the surface area is much more than a square foot. 
    Hot_water_fan
  • JakeCK
    JakeCK Member Posts: 1,130
    To elaborate on the hx and the principles it operates on:

    The total interior surface area of the waste pipe is roughly 1200 sq in if I did my math right. Or about 8.4 sq ft. But that isn't the whole story. As the waste water drains it sticks to the ID creating a thin water film as it falls. If we really want to dig in we could start talking about the shape of water molecules and the slight differences in charge and all that chemistry and physics but that is beyond this conversation. Bottom line the waste water sticks to the ID as it falls straight down and, if plumbed right using counter flow, the fresh cold water enters the bottom of the hx to maximize delta T. The faster the fresh water flows the more you recover. This is why you want to have it piped to both go to the tank and the cold side of the shower faucet. And if you are using a tempering valve or thermostatic valve piped to both sides of that as well.
  • spd1980
    spd1980 Member Posts: 47
    Hi, Just to get into the weeds a bit on some different aspects of this. First, GPM of the showerheads... Not all of the water coming from the showerhead is hot. Normally the percentage of hot water coming from the showerhead is 50% to 70% of the total, so even with your 3 GPM head, it's using at most 2.1 GPM of hot water. This suggests that the system REALLY isn't keeping up with demand. Next, low flow showerheads can actually feel better than high flow. The better heads produce large water droplets, which hold heat better than smaller droplets and the lower flow reduces friction losses in the piping, so you get more pressure/faster moving and bigger/hotter droplets hitting you. This particularly matters because the water cools substantially traveling from the showerhead to the bather. Men have less of a problem with this because we're generally taller. Just that little difference in height can give women noticeably cooler water. To test this, feel the temp of the water right at the showerhead and again three or four feet away, with the same hand. You'll notice the difference. Here's an image of the Delta showerhead I mentioned. It's a quick, inexpensive fix that you will probably want to keep. Next is the shower heat exchanger. Sized for best performance, you'll see that a shower heat exchanger can capture 60% of the otherwise lost heat, basically doubling the showering time. Here's a link to information: https://renewability.com/reference/ Of course, you'll need a place to install it vertically. I installed one in my home and plumbed it so that it feeds warmed water to the cold side of the shower. This is simple plumbing, though I usually need to adjust the temperature down or the shower gets too hot. Third is that you can only expect to get 70% to 75% of the volume of your water tank as undiluted hot water. So, at best, you can get 33.75 gallons of hot water from your present tank, plus how much water gets heated as you shower. Sorry for the long post, but hope it helps! Yours, Larry
    Thanks for the detailed reply. There’s a lot of good talking points to explain the benefits of a low flow shower head and the performance of your heat exchanger solution sounds really promising. 
    Larry Weingarten