Reducing 2 hot water heaters to 1.

[ajohansson]

Fair warning this is long...

Been in this tract home for 1 year now. It was originally built 15 years ago. Had 2 - 40 gallon atmospheric vented hot water heaters in the garage when built. Shared same 4" vent pipe up to second floor roof. . We bought it from the original owner. At some point he replaced both of them and decided to go to a 50 gallon on one and left a 40. When the inspector went through the house he noticed one bathroom up stairs had no hot water. Went to the hot water heater and one was on with pilot lit and the other had no pilot. The one that was off fired right up and he went about his inspection. He checked on it 2 hours later and it was still lit and just happened to mention it to me that there may be an issue with it down the road and that it was manufactured in 2008 and had a 12 year warranty. He also said the first water heater inline that was out goes to the second floor bathroom and the loops back down and feeds the second water heater that feeds the rest of the fixtures in the house which includes 3 full baths, kitchen/dishwasher and laundry room.

So We move in last March. No issues with the water in the home other than the inspector didn't check the water pressure as I find it at 105 psi. A whole other issue that I already solved.

So come winter this year (in so cal but it gets into the low 30s and high 20s a couple weeks a year for overnight lows) that water heater will go out. Super random. I call us craftmaster they tell me to replace thermocoupler. I do that. Still randomly will shut off but always lights up immediately. US Craftmaster sends me a new gas control valve. I put that in and still randomly shuts off. I do some research and start checking for back draft. Well the 40 gallon one always backdrafts when the 50 and 40 are on at the same time. I talk to a friend of mine whos father is a plumber and he thinks that potentially since the 50 has a bigger burner and combusts more, that the shared 4" vent pipe cant handle all the combustion and that its happening in the winter because of the heavier denser cool air. He thinks that's why its so random and all spring and summer we were fine. He also thought it was strange how one water heater went upstairs to the bathroom and then fed the second water heater. He mentions maybe going to one 75 gallon water heater.

So since the 50 gallon heater was a 2013 and 40 was having issues I got rid of the 40. We had been taking for back to back showers with the 50 with a thermo-mixing valve so I felt confident just staying with the 50 gallon and into going to a 75. The drywall finished water heater stand was in sore shape so I demolished the box and rebuilt it with water resistant hardibacker ( i love it by the way I can stand on it and no drywall texture getting jacked up) I should say i finished it with hardibacker I did use 5/8 drywall for firecode just put the 3/8 hardibacker on it. I also made it smaller and created room for a slop sink in the garage for a future project.

So I get water heater in and I kept the plumbing the same. Hot water went up to second floor bathroom and then I just looped the pipe in the garage that fed where the second water heater was. That was a mistake as I had horrible water pressure at my shower which is at the end of the line from the original second water heater. So I changed it up so the hot water out is inline with the feed to the majority of the fixtures and it has a T to the bathroom on the second floor and I capped the return line. This improves flow dramatically in my shower. I leave my shower going and turn on the bathroom shower on second floor that is off the T and it is flowing well. I go back to my bathroom and its reduced. Not dramatically but I used to be able to run both showers simultaneous with great pressure

So how could removing a water heater that is just storage vessel that does not have a bladder in it and doesn't regulate pressure cause a reduction like this? I started to think since I moved the water heater around so much taking it down and putting it back up perhaps I dislodged a bunch of scale. I flushed it again and lots of white scale rocks come out. Could that be the issue perhaps? We have hard water and my water heater sounds like a microwave with a bag of popcorn in it so I'm hoping there isn't an issue. But I do have a cash-acme thermal mixing valve that has a screen on its inlet so that shouldn't be the case. I just put in new screens but I guess they could be clogged potentially which is something I will check but if that's not it from hydraulics point of view did the way I decide to plumb it sound correct? Would removing the second water heater cause a volume issue like this?

here is a diagram of old and new.

Any help appreciated.

AJ

 

[Dana]

You're using the term "pressure", but what you really mean is flow.

You can have high pressure on a skinny restrictive line that has very little flow when you open the tap. If the total plumbing path has increased or the diameter of the pipe is smaller, it'll have less flow at the end of the pipe. If you gobbed a bunch of solder when you cut in the tee, that could cause a restrictive point too. The possibilities are many.

What diameter of pipe, and how long? What do you mean by "...capped the return line..."? Was that an alternate supply path to that bathroom?

Raising the storage temp and mixing it down to a safe temperature before it enters the distribution plumbing will increase the apparent capacity of the tank, but it won't improve the flow.

Raising the temp of the cold water feed (and the feed to the water heater) with a drainwater heat exchanger lowers the flow requirements on the hot water side, saves fuel, and increases the apparent capacity of the tank (for showering, not for tub fills) but it's an expensive fix for a flow problem.

 

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[ajohansson]

You're using the term "pressure", but what you really mean is flow.

You can have high pressure on a skinny restrictive line that has very little flow when you open the tap. If the total plumbing path has increased or the diameter of the pipe is smaller, it'll have less flow at the end of the pipe. If you gobbed a bunch of solder when you cut in the tee, that could cause a restrictive point too. The possibilities are many.

I used sharkbite so no solder. Same 3/4" all the way. The size of the overall run didnt really change all I did was remove the second water heater.

What diameter of pipe, and how long? What do you mean by "...capped the return line..."? Was that an alternate supply path to that bathroom?

3/4" pipe I have no idea how long it is. There is no alternate feed to the bathroom. I know this because if the first water heater went out that bathroom never got hot water. If it had an alternate feed it would have hot water from the second water heater. As far as the capped the return line. If you look at the diagram I put a link to. The first water heater went to a bathroom and then came back to the garage and fed the second water heater and then went out of second water heater to the rest of the house. Since I removed the second water heater, the line that came to feed the second water heater was capped.
[/QUOTE]

Raising the storage temp and mixing it down to a safe temperature before it enters the distribution plumbing will increase the apparent capacity of the tank, but it won't improve the flow.

Totally agree with that.

raising the temp of the cold water feed (and the feed to the water heater) with a drainwater heat exchanger lowers the flow requirements on the hot water side, saves fuel, and increases the apparent capacity of the tank (for showering, not for tub fills) but it's an expensive fix for a flow problem.

Not following. I don't have a drain water heat exchanger.

So we took some showers yesterday and it does seem to be improving. Maybe some air in the lines causing an issue? I need to look at this more.

AJ

 

[Dana]

It's possible that unless you can see the entire run of what you're referring to as a "return" line had other things on it, creating something of a loop in the distribution system, and that is somehow changing the overall flow characteristics.

Plumbing in separate 3/4" home-run supply lines from near the tank to each bathroom would be a lot cheaper than drainwater heat recovery, and is pretty much guaranteed to fix any flow issues in the distribution plumbing, which would narrow it down to flow restriction at or near the tank.

Air in the lines will not reduce flow. It may hiss spit and chug a bit as it purges the air, but there's no way air can slow down the flow.

I understood completely that you don't have a drainwater heat exchanger, but was pointing to that as a possible (but expensive to implement) solution to the apparent insufficient flow condition. A drainwater heat exchanger takes heat out of the outgoing drain and puts it into the incoming cold stream. With 70-75F water entering the cold side of the shower mixer instead of 40F water, the amount of 130F-140F water flow needed to achieve 105F at the shower head drops dramatically, and increases the amount coming from the cold water side. Feeding the same 70-75F water into the water heater reduces the amount of fuel needed to raise the tank back up to 130-140F, reducing recovery time, and overall fuel use.

To get a meaningful amount of heat recovery and performance boost takes at least a 40" section of vertical drain (more is better), at 4" diameter, or 55" x 3" diameter. The biggest one that fits is the right one, since the marginal improvement in performance more than makes up for the marginally higher cost of the bigger heat exchanger. The heat exchanger doesn't have to be close to the water heater to work, since it's roughly room-temperature water coming out of the heat exchanger. A 4" x 36" runs $750 from one vendor but only delivers 40% heat recovery (at 2.5gpm under a NRCA test protocol conditions) whereas a 4" x 60" runs about a grand, delivering about 55% efficiency. At flows lower than 2.5gpm the recovery efficiency is higher. Definitely not cheap, but it makes a difference, and for a 3-4 person daily-showering household it will pay for itself in under 10 years at a buck a therm. At most CA type incoming water temps a 4" x 60" turns a typical 50 gallon tank into a an "endless shower" experience too.

But it doesn't do a thing for batch draws such as tub fills.

 

[ajohansson]

It's possible that unless you can see the entire run of what you're referring to as a "return" line had other things on it, creating something of a loop in the distribution system, and that is somehow changing the overall flow characteristics.

I don't know how there would be anything other than one long run. If that first water heater was out and the second one was working it only affected the one bathroom up stairs. I checked all other fixtures in the house and they all had hot water except the one upstairs bath. If the first water heater fed something else or happened to be tied into the rest of the house seems like the hot water would have a reduced temperature at the outlet. All other fixtures had hot water at them.

My theory I have to think is correct on how its plumbed. The first hot water heater for whatever reason was plumbed to go to the second floor and service one of the bathrooms up stairs then was plumbed back downstairs to the garage, exited the wall and was fed into the second water heater. This second water heater then went to the rest of the fixtures in the house which was 2 more bathrooms upstairs, a bathroom downstairs and kitchen and laundry room. Why it was done this way is beyond me.

All the bathrooms have great pressure/flow on them right now. I haven't rechecked with the isolated bathroom and my shower on again for a reduction in flow/pressure but will do when I get some time. Right now nobody is complaining in the house so I guess we are alright.

I do have a question on setting the pressure in the house though. Should I sent my PRV to flow or static pressure. What I mean is should I open up a couple showers and say the kitchen sink and then set my prv? based on adequate flow? Right now its set at 50 psi static and when a couple showers go on its drops to about 48 psi.

 

[Dana]

48-50psi is just fine. Leave it there, lest we steal defeat from the jaws of victory.

If the "return" line is fairly long between where it had been connected (now capped) and the water heater, and conceivabley could be put to re-use as a supply line, if higher flow is needed