Which water heating method

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bikeboy

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In the home I'm presently living there's 2- 50 gallon electric water heaters opposite ends of house; (aprox. 50ft apart). One takes care of kitchen sink and 2 full baths with a long pipe run to termination. The 2nd heater has a slightly less distant pipe run which takes care of a laundry (tub and washer) and Master bath which contain a Shower, double sink, and 84 gallon whirlpool tub. I was hoping the 50 gallon water heater taking care of the Master bath would allow the tub to fill @ aprox 120 deg. it will 2/3 fill w/ hot water. The rest needed we fill it with hot water from stove! Not convenient. Also; the other end w/kitchen and 2 baths, achieving hot water is slow and a 60 ft pipe run to termination. I considered to replace the WH for the master bath w/ the whirlpool tub w/a tankless unit for the master bath. Then I considered to just use a higher gpm Navien tankless w/ built-in circulator and just replace both water heaters. But then I thought, why not just use both existing water heaters there with a circulator; allow the 1st HTR to fill w/ cold , take hot to 2nd WH cold side, then 2nd WH hot side back too 1st WH drain valve to keep circulation using 3/4 for circuit main ? I figured I could get a 100 gallons at hand which is circulating thru both units, and use for whirlpool tub when needed. I figure the 2nd WH would be only maintaining temps as a holding tank, and both would be still be cost effective when not in unusual use. Please tell me the drawbacks of this system, or how to be connected in different way to work efficiently, tankless or other way. There's only 2 of us , so not big daily hot water demand. A diagram would be helpful.

Thank you; and please reply.
Howard.
 

Phog

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The cheapest and least intrusive option would be to install a thermo mixing valve kit on the water heater that needs to fill the tub. Then crank the temperature way up. This will increase the amount of 120F water you get out of it. But maybe still not enough for your tub.. it would be close.

Another way to go without buying new equipment would be to run the tanks in series, aka outlet from tank #1 to inlet of tank #2, then outlet of tank #2 to rest of house. (Then optionally install a recirculation system to keep the hot water wait times down at the bathrooms.) Putting the two tanks in series will perform exactly like you have a single 100gal tank, and will guarantee you can fill your 85gal tub full. The best way to do this would be to move one tank next to the other. In theory you could do it without moving the tanks but the plumbing would end up being long runs all over the place, kind of a mess.

If you're looking to get different equipment, there are a bunch of other options. Some of which could reduce your monthly operating cost, but all of which would be significantly more expensive upfront.
 

bikeboy

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The cheapest and least intrusive option would be to install a thermo mixing valve kit on the water heater that needs to fill the tub. Then crank the temperature way up. This will increase the amount of 120F water you get out of it. But maybe still not enough for your tub.. it would be close.

Another way to go without buying new equipment would be to run the tanks in series, aka outlet from tank #1 to inlet of tank #2, then outlet of tank #2 to rest of house. (Then optionally install a recirculation system to keep the hot water wait times down at the bathrooms.) Putting the two tanks in series will perform exactly like you have a single 100gal tank, and will guarantee you can fill your 85gal tub full. The best way to do this would be to move one tank next to the other. In theory you could do it without moving the tanks but the plumbing would end up being long runs all over the place, kind of a mess.

If you're looking to get different equipment, there are a bunch of other options. Some of which could reduce your monthly operating cost, but all of which would be significantly more expensive upfront.
 

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Thanks for reply; Before I would buy a mixing valve, even when therm is turned to near 160, still not hot towards the end of the tubs fill, probably cause the ground temp is too cold. the two water heaters are opposite ends of house, but the plumbing end runs for both heaters run close to each other. I was figuring I could just increase those main runs to 3/4 and tie them together. Install circulator anywhere on main line. The last run would end up at the 1st heater at the drain valve to complete circuit. the circulator could operate thru a flow switch, or timer. I'm not sure if that's at all energy efficient.

Howie
 

Dana

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Plumbing the tanks in series ( the output of one feeds the cold-in of the other) and using a demand type recirculation scheme can work.

There are no great tankless solutions for this- the max flow of even a 199KBTU gas fired tankless is still going to be pretty tedious for filling an 84 gallon tub, more so in winter.

The napkin math on that:

84 gallons is ~700lbs of water, and at 40F in (wintertime incoming water from the mains), 110F at the spout is a 70F rise, so you're looking at a total of 70F x 700lbs = 49,000 BTU for a tub fill. The output of a condensing 199K tankless is about 190,000 BTU/hr so to deliver 49KBTU takes 49K/190L= 0.26 hours. 15-16 minutes. Filling the tub from tank type water heaters would take half the time, assuming you have fat enough plumbing and sufficient water pressure behind it.
 
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Phog

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For putting the tanks in series, you first need to choose the order, aka which tank you want to be upstream and which downstream. Let's call upstream "tank #1" and downstream "tank #2". Then:

1. Disconnect the hot line from tank #1
2. Disconnect cold line from tank #2
3. Connect new dedicated line from tank #1 hot to tank #2 cold. (NOTHING taps off this new intermediate line, it's just a straight shot)
4. EVERYTHING that used to get its hot water from tank #1 hot now needs to be replumbed to tank #2 hot

To install a recirculation, typically:

1. Install a pump on hot outlet of tank #2. Timer activated is common but there are other ways to do it too such as thermostat sensor
2. Run a return line from the farthest point in hot water system back to cold inlet of tank #1.
3. Use a check valve in this return line to prevent reverse flow. Insulate this line too.

Hope this helps
 

bikeboy

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For putting the tanks in series, you first need to choose the order, aka which tank you want to be upstream and which downstream. Let's call upstream "tank #1" and downstream "tank #2". Then:

1. Disconnect the hot line from tank #1
2. Disconnect cold line from tank #2
3. Connect new dedicated line from tank #1 hot to tank #2 cold. (NOTHING taps off this new intermediate line, it's just a straight shot)
4. EVERYTHING that used to get its hot water from tank #1 hot now needs to be replumbed to tank #2 hot

To install a recirculation, typically:

1. Install a pump on hot outlet of tank #2. Timer activated is common but there are other ways to do it too such as thermostat sensor
2. Run a return line from the farthest point in hot water system back to cold inlet of tank #1.
3. Use a check valve in this return line to prevent reverse flow. Insulate this line too.

Hope this helps









Thanks for reply , after running the dedicated line from T1 to T2 ;couldn't I just use T2's hot line to continue hot water circuit in 3/4 to cold side of T1 being hot water loop is on a circulator?

Howie...
 

Phog

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Thanks for reply , after running the dedicated line from T1 to T2 ;couldn't I just use T2's hot line to continue hot water circuit in 3/4 to cold side of T1 being hot water loop is on a circulator?

You could, but you would be recirculating the hot water only inside that loop instead of all the way to the farthest point of use. So there would still be some delay in getting hot water at the fixtures. If your goal with recirculation is to minimize the wait, the best way to accomplish this is to get the pipes charged up with hot water all the way to the point of use. (So the hot water is already there as soon as you turn on the shower, faucet, etc.) What you're describing gets the pipes charged up with hot water only part way. That said, every house's plumbing is different & if you think you will see sufficient improvement in your house from the loop as you envision it, and you're comfortable that it's money well spent, then absolutely go for it. Just make sure there's a check valve appropriately placed in the return line, and insulate the pipes wherever you can.
 

Jadnashua

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There are lots of recirculation kits, and you can make up one yourself. One of the kits that I have is from RedyTemp (no association with them). It's essentially self-contained with the check valve, sensing, and pump all in one box. I have it at my master bath vanity. Everything else is closer to the WH, so it works for me. Mine was installed in 2005 or so and has been working faultless. It can use an add-on timer. I've had to replace a couple of those over the years. The SS ones seem to last longer than the clock-works ones. Those are pretty generic, just make sure you get one designed to work with a motor. The motor is quite small, so most should work. You don't want to over pump things, that can lead to wearing the pipes out from the insides and water noises from the high speed flow. Slow works just fine.
 

bikeboy

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You could, but you would be recirculating the hot water only inside that loop instead of all the way to the farthest point of use. So there would still be some delay in getting hot water at the fixtures. If your goal with recirculation is to minimize the wait, the best way to accomplish this is to get the pipes charged up with hot water all the way to the point of use. (So the hot water is already there as soon as you turn on the shower, faucet, etc.) What you're describing gets the pipes charged up with hot water only part way. That said, every house's plumbing is different & if you think you will see sufficient improvement in your house from the loop as you envision it, and you're comfortable that it's money well spent, then absolutely go for it. Just make sure there's a check valve appropriately placed in the return line, and insulate the pipes wherever you can.


The loop would pass within a few feet of any fixtures as would any main. I'd input WH1 cold, that hot water out would basically start the loop, and pass wh1 branches (3/4) mains all the way, continuing to cold side of wh2, power connected, and no cold water input from house. The cold side of wh2 receives hot water from wh1 then hot out in 3/4 passing wh 2 branches, and back to either cold side wh1, or wh1 drain valve; and that hot water would circulate both wh branches w/ hot water. in this way, there are no non functional piping in the loop.

Howie
 

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The branches that tap off the connecting pipe section between wh1 and wh2 will have access to only the 50 gallons in wh1 in your scenario here, and will run out of hot water at the same rate as before. Only the branches that tap off downstream of wh2 will have access to the full 100 gallons from both water heaters. (The recirculation will not return much if any usable hot water from wh2 to wh1, so to get 100 gallons of hot water you need to draw off wh2). A bit unconventional to have the tanks separated & to draw off the interconnection pipe, but hey if it works for you great. Just make sure your big tub gets its water from pipes downstream of wh2 & not from that middle section between the two tanks. Good luck
 
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bikeboy

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The branches that tap off the connecting pipe section between wh1 and wh2 will have access to only the 50 gallons in wh1 in your scenario here, and will run out of hot water at the same rate as before. Only the branches that tap off downstream of wh2 will have access to the full 100 gallons from both water heaters. (The recirculation will not return much if any usable hot water from wh2 to wh1, so to get 100 gallons of hot water you need to draw off wh2). A bit unconventional to have the tanks separated & to draw off the interconnection pipe, but hey if it works for you great. Just make sure your big tub gets its water from pipes downstream of wh2 & not from that middle section between the two tanks. Good luck

OK, so could I take any low draw branches between wh1 towards wh2 in the loop, then wh2 coming back to finish loop @ mast. bath (whirlpool tub), then into cold of wh1. If not; then I guess ide have too tap all the branches off of run between wh2 return loop back to wh1. For the loop coming back, is it better to tap cold side or drain valve of wh1 ? Thanks...
 

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OK, so could I take any low draw branches between wh1 towards wh2 in the loop, then wh2 coming back to finish loop @ mast. bath (whirlpool tub), then into cold of wh1.

Yes exactly, if plumbing things this way is easier & as long as you don't care that some low draw branches will run out of hot water sooner. Like whenever someone fills up the big tub, wh1 will get completely drained and those branches drawing from the in-between pipe will only get cold water. Even though wh2 still has some hot water left.

If not; then I guess ide have too tap all the branches off of run between wh2 return loop back to wh1.

Having the two water heaters side by side would make it so that you only have a short run between the tanks, and then everything comes off wh2. And then everything in the house gets full access to all the hot water all the time. Which is why most people do it that way & what you're proposing is uncommon.

For the loop coming back, is it better to tap cold side or drain valve of wh1 ?

Really doesn't matter from a functional standpoint. The recirculation return water ends up at the same place either way. Your local codes may have a preference.
 

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When setting up a recirculation system to code on new construction both the supply and return lines need to be insulated with R3 pipe insulation. In a retrofit this isn't always practical, but it's worth insulation whatever plumbing is reasonably accessible.
 

bikeboy

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Yes exactly, if plumbing things this way is easier & as long as you don't care that some low draw branches will run out of hot water sooner. Like whenever someone fills up the big tub, wh1 will get completely drained and those branches drawing from the in-between pipe will only get cold water. Even though wh2 still has some hot water left.



Having the two water heaters side by side would make it so that you only have a short run between the tanks, and then everything comes off wh2. And then everything in the house gets full access to all the hot water all the time. Which is why most people do it that way & what you're proposing is uncommon.

Is there any benefit to having these 2 water heaters in this operation over using a high GPM tankless? Howie...

Really doesn't matter from a functional standpoint. The recirculation return water ends up at the same place either way. Your local codes may have a preference.
 

Phog

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Is there any benefit to having these 2 water heaters in this operation over using a high GPM tankless? Howie

See Dana's post above, he does the math on how long it will take to fill the big tub using the biggest tankless on the market.

If you're thinking of spending a lot of money on new equipment, and gas is an option, then you should be including other options in your decision making process as well. Such as a gas-fired tank water heater, or even integrating your hot water & home heating needs into a single appliance.

But still by far your cheapest option is to just reconfigure your existing tanks as we've discussed.
 

bikeboy

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See Dana's post above, he does the math on how long it will take to fill the big tub using the biggest tankless on the market.

If you're thinking of spending a lot of money on new equipment, and gas is an option, then you should be including other options in your decision making process as well. Such as a gas-fired tank water heater, or even integrating your hot water & home heating needs into a single appliance.

But still by far your cheapest option is to just reconfigure your existing tanks as we've discussed.
 

bikeboy

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OK; i'm using 2 heat pumps for hvac. Will a 50 gallon gas water heater be able to keep up with that 84 gallon demand for the mast bath zone(including tub), and if so; could that alone be used for what I'm trying to do w/ a circulator ?
Also; using the 2 electric water heaters together as we discussed, wont wh1 be over worked and have a shorter life span and wh2 be passive since it's being fed w/ hot water to the system ?
Howard...
 

Phog

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For a gas water heater I would be looking at installing a single 75 gallon high recovery gas water heater coupled with a thermostatic mixing valve. For example the Honeywell mixing valve that this forum links at the top, plus a water heater similar to:

https://www.supplyhouse.com/AO-Smit...dential-Gas-Water-Heater-w-Side-Connection-NG

Can you tell us more about your heat pumps? Any spare heating capacity there?
 

Jadnashua

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Unless you end up with a commercial WH with a huge burner, a 50-gallon one won't fill your 84-gallon tub...it just can't produce enough hot water and the tank size is too small. Say you have a fairly common 1/2" fill valve at the tub, that's about 5-gallons of hot and one of cold for a typical fill or so. At 6gpm, it will take 16-minutes to fill the tub. A larger fill valve will be better, or worse, depending on how you look at it. That's not much time to reheat the incoming water, and even less if you have a bigger fill valve.
 
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