Thread: Water heaters in tandem and odd-looking draft hood

I inspected a home with 2 water heaters connected in tandem. The current owner says one heater (75 gallon) is for primary use and the other heater (40 gallon) is a spare in case the primary heater fails. A few issues I need help with:

1. Is the draft hood and vent pipe for the larger heater installed correctly? I have not seen a confuguration like this and it looks odd to me. I suspect that it's not correct but need help to document reasons in my report. FYI, the vent pipe is incorrectly pitched back towards the heater. There is a lack of headroom and other obstructions before the vent pipe can properly connect to the flue vent.

2. The spare water heater is shut-off but I wonder if there's any negative consequences if both heaters are left in the open position and used simultaneously. I wonder if each heater should have its own expansion tank.

After seeing the pictures, if you see other problems please post and would like to open it it for discussion on this thread.

Thanks.

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That does look different from what you would normally see. I would get hold of the manuals for both heaters to see what the manufacture requires for venting. Supply the manuals (or links to the manuals) to the buyer and that should end your involvement.

I'm sure everyone is trying to figure out the piping instead of answering your question. I mean, what the heck! Rube lives!

As far as the venting, well same guy! I have never seen a water heater share a draft hood with a furnace, or what ever that is behind the water heaters. Looks like the large water heater might be a direct vent type but the vent/flue looks like single wall? If it is power vented, you sure would not want to dump it into a draft hood!

The 40 gallon vent goes straight into an elbow, no vertical rise after the hood. Not good.

You might want to ask how many water heaters have failed to require a hot stand-by?

Galvanized vent pipe is a no go.

The only things I see that are correct: 1) the water heaters are right side up. 2) they do have dirt legs installed.

Those vents would be just fine..........if they were electric water heaters.

Vern....It's not a direct vent. I looked up the specs (Bradford-White model M-I-75S6BN) and it's a "Residential Atmospheric Vent Gas Water Heater". Not sure what "atmospheric vent" means but it's a conventional hook-up as far as I can see.

Rod...why is galvanized pipe a no-go? It's a common occurence that I see. I just need back-up details to support my comments.

Thanks all.

Originally Posted by Stanley Chow

Vern....It's not a direct vent. I looked up the specs (Bradford-White model M-I-75S6BN) and it's a "Residential Atmospheric Vent Gas Water Heater". Not sure what "atmospheric vent" means but it's a conventional hook-up as far as I can see.

Rod...why is galvanized pipe a no-go? It's a common occurence that I see. I just need back-up details to support my comments.

Thanks all.

It is wrong. The newer Bradford White does not even have a draft hood/collar on it. The vent pipe is connected directly to the unit. As for galv. pipe, I'm guessing Rod was saying that it is not a B Vent pipe and single wall (if that is what it is) is not a good thing.

Scott....My apologies but I don't understand your reply. What are you saying is wrong? The installation or the replies? The manufacturer does show a draft hood/collar (see attachment); but actual installation is a direct connection as you can see in the picture.

Also, are you saying that double-wall type B vents are never galvanized?

I appreciate assistance from a seasoned pro like you and others.

Stanley, atmospheric vent means it relies on atmospheric pressures to vent, no fan involved. So it has to have a draft hood, it's own draft hood!

Here is a link to what might be the manual for your water heater. I would not try to tell them how to fix the problem unless you are a licensed plumber.


http://www.bradfordwhite.com/images/...-44219-00J.pdf

One expansion tank is enough, AFAIK, provided both tanks connect to the same pipe there. With all those shutoffs it's hard to tell.

I think it may be possible to run those tanks in parallel as well as in series? But you'd need a guide book to get the valves all set right.

As the others have said, the exhaust vents are both wrong, and the vent on the big tank is very wrong. Instead of routing those vents around obstructions, he should have removed or altered the obstructions so the tanks can be vented properly. People don't seem to realize they are dealing with a poisonous gas in their basements.

Ok I want to address the water piping. I would of plumbed them in where both work in parallel with a first in last out piping. Its hard to tell how they have that piped with the current pictures.

Now for the draft hood, or lack off on the larger Bradford White water heater. First time I came across a water heater that had the venting connected directly to the after heater I was like what the... So I called the local building and plumbing inspector to see the current install and asked them what that was all about.

So they came over and educated me. When a water heater or any gas appliance that needs to be vented to a chimney can not use a draft hood due to its height you can direct connect the venting to the top of the heater or appliance, and vent through a draft box. A draft box is a square box the appliance vents into and the bottom of the box is open to draw its air from and then vents to the chimney from the draft box.

From the looks of the third photo its hard to tell but it does look like a draft box was installed.

Thanks Ron, that's a new one on me. (This is the greatest board!)

Originally Posted by Ron Hasil

..
. When a water heater or any gas appliance that needs to be vented to a chimney can not use a draft hood due to its height you can direct connect the venting to the top of the heater or appliance, and vent through

From the looks of the third photo its hard to tell but it does look like a draft box was installed.

.
The Vent Still must have the proper 1/4 inch Rise Per Foot.
* this install appears to have a Negative Slope.
.

WOW !!! Ron...You are an amazing person. This was worth a Harvard education.

Yes there is a square box installed next to the heater. I was wondering what it was for. Now we all know.

Billy....I agree that the vent pipe still needs to be pitched in the right direction.

Thanks a million Ron...and everyone for helping on this one.

That would not fly in NC. The code section on gas vents is below.


503.6 Gas vents.

Gas vents shall comply with Sections 503.6.1
through 503.6.12 (see Section 202, Definitions).

503.6.1 Installation, general.

Gas vents shall be installed

in accordance with the manufacturer's installation instructions.

Regardless of what the local yahoo AHJ says, it boils down to what the manufacturer(Bradford White) approves. If BW requires a draft hood then it must have one, in the eyes of doing it properly.

A draft box might work very well, but that does not mean it is correct unless the appliances manufacturer has it as an option. And after review in a BW install manual I did not see a draft box as a approved substitute for a draft hood.

Thing is it does have a draft hood, just not one you are used to seeing. Later when I get home I find some documentation to show you that the use of a draft box is approved.

Scott and Ron.....I appreciate your input in this odd situation. I am about to complete my report and obviously it's very important that the information is correct and I use the correct verbiage. I'll wait for Ron's followup later today.

Thanks again guys. I am very appreciative of your assistance.

Well I talked to a Bradford White Tech support. They informed me the draft box may work, and was an acceptable way of venting 30+ years ago. But with todays heaters he said "The heater must be used with the supplied draft good. The heater is designed and certified to be run with the draft hood and no other way." So that clears things up for me as well as you guys.

Ron.....Thanks again very much.

Stan

As noted:
1. the mfr's instructions take precedence.
2. single wall, type A, venting is approved for the above situation.
3. galv. venting is also approved.
4. Selkirk metalbest catalog/site is a useful reference.

5. linked water heaters are typically installed "In Series" or "In Parallel", the above situation would be best served by a Parallel installation. With apologies to Ron Hasil, "first-in last- out" is a "Series" installation.
6. perhaps Ron would help me out here? as far as i know, both W/H's have to be the same capacity? eg 40gal? Is this correct?
is the draft box the sheet metal box behind the W/H's?
venting W/H's and FAC's into a common vent is a typical, approved practice?
7. gas supply to two w/h's should be in 3/4 to the tee and then in 1/2 to each gas valve.
8. unions are not permitted on gas lines.
9. the water lines cannot be disconnected without cutting, w/h's must not be fixed in position this way.
10. the T&P's discharge to interior floor.
11. the anodes appear to be covered by the venting arrangements.

Perhaps i am quoting local codes and practices. Please fire away.

I meant to add the following:
12. UPC determines that single wall venting may not pass thro any wall, floor or ceiling.
13. UPC also req's that for two w/h's the common connector must be the diameter of the larger w/h vent plus half the diameter of the smaller w/h vent. So, for the example in the pics, if the larger w/h diameter is 6" and the smaller 4" then the common connector will be 8".

In NC: (for a start)

#5 - There is no right or wrong way.
#6 - They do not have to be the same size.
#8 - Only applies in concealed locations.

Originally Posted by tom daley

As noted:


5. linked water heaters are typically installed "In Series" or "In Parallel", the above situation would be best served by a Parallel installation. With apologies to Ron Hasil, "first-in last- out" is a "Series" installation.
6. perhaps Ron would help me out here? as far as i know, both W/H's have to be the same capacity? eg 40gal? Is this correct?
is the draft box the sheet metal box behind the W/H's?
venting W/H's and FAC's into a common vent is a typical, approved practice?
.

Well you are wrong about first in last out it is a parallel install. Here is a picture so you may understand. The cold of each water heater is hooked up to each other as well as the hot. It is just not working on a balanced equal split of the heaters. The cold water enters the first heater first , then the second heater last, the hot water leaves the second heater first, and leaves the first heater last. In series, the hot of the first tank would enter the cold of the second tank. As you can see this is not the issue.



Now if you want to pipe it in a traditional parallel piping both heaters must be exact in size (gallons and BTU's) Typically for it to work proper even the same make and model tank, and the piping must be identical between each heater where they tie into the tee fittings. Meaning same amount of pipe turns and fittings, otherwise one heater will flow more water into the building than the other and will fail first from working more than the other.

Originally Posted by tom daley

As noted:

7. gas supply to two w/h's should be in 3/4 to the tee and then in 1/2 to each gas valve.

When I zoom into the photo ot looks like the piping to the tee's are larger than the pipe going into the gas control valve on each heater. It is accapble to plumb 3/4" right up the first heater then branch off to each heater with 1/2" pipe as long as the gas pip sizing will accomdate the BTU's of the heaters.

Originally Posted by tom daley

As noted:
8. unions are not permitted on gas lines.

Then tell me how are you to take apart the gas lines to replace the gas control valve or heater? Unions are required right after the shut off valve to each heater.

Originally Posted by tom daley

As noted:
9. the water lines cannot be disconnected without cutting, w/h's must not be fixed in position this way.

You are correct unions are required at each heater water pipe connection. Typicaly a dielectric union or a brass union would be used at the tank.

Originally Posted by tom daley

As noted:
10. the T&P's discharge to interior floor.

This is the way its done here in Illinos as long as they discharge within 6" of the floor. Also as long as the discharge can not do any damage ie on second floor installs it has to be ran to a drain with an airgap.

Originally Posted by tom daley

As noted:
11. the anodes appear to be covered by the venting arrangements.

The Bradfor Whites any many other manufactures are putting the anode rods in the hot discharge side of the water heaters. So when it comes time to replace the anode rod you undo the hot water piping and unscrew the manufacture nipple which the anode rod is attached to.

James and Ron, thank you for your replies:
5. I didn't claim a right or wrong way for tandem w/h installs in general. I merely referred to the conventional terminology (this is a site of record), and said that Parallel w/h's would "best serve" that particular situation. Why? Because one w/h will always be redundant, and in Parallel w/h's would enable a simple switch-over. Whereas, in Series w/h's would req. re-piping work to switch from one to the other.
5. cont. Ron, I do understand Parallel & Series installs, and thank you for your clear pics. If you care to post a Series schematic it will show what to me is "first in last out" that is,one c/w "first in" & one h/w "last out". However, as your pic shows Parallel has two c/w "first in's" & two (h/w) "last out's", that to my mind is not "first in last out".

6. This is a contentious point for the very reason(s) Ron has pointed out. However, where one w/h is redundant the point is irrelevant, but where two unequally sized w/h's are active in Series then it's an issue.

7. Well spotted, the gas supply is indeed in 3/4" with 1/2" branches at the gas valve. My ref. (which i should have made clear) was to a balanced gas supply for parallel w/h's.

8. James, thanks for the "concealed areas" reminder. Ron makes the further observation ref. disconnection. For what it's worth, California pb. inspectors are down on any unions after the meter. Flex conn's are req. after the isolator.
Right and left couplings are, weirdly, allowed.

11. Thank you for the info ref. Bradford White's practice of supplying combo anodes.

My bald statements are not to display my two cents worth but to tease out your ten cents worth that i might learn from you all - if i only listen to myself then i will end up like the character who thought that Col. Gadaffi was the guy who started the fried chicken thing.

When we plumbers say first in last out we are speaking of the first water heater It has the cold coming in first and the hot is the last to leave where the second heater is the last heater to get cold water but the first to put out the hot. Here I labeled my drawing to help.



And here is a series hook up.



As for gas piping and water pipe hook up here in Illinois the water heaters are to be hard pipe at the hot and cold pipes as well as the gas pipe. But with the unions as needed. Also the expansion tank is not to have any shut off valves after it per plumbing code.

[quote=Ron Hasil;176917]When we plumbers say first in last out we are speaking of the first water heater It has the cold coming in first and the hot is the last to leave where the second heater is the last heater to get cold water but the first to put out the hot. Here I labeled my drawing to help.


To be even a little clearer---you are actually talking about the devices and their placement, not the flow of water that could actually change depending how the valves are set.

Ron (and everyone else),

When diagrams are posted, it is very helpful (to me anyway) if they are sourced.

Thanks in advance.

MDT

Originally Posted by Michael Thomas

Ron (and everyone else),

When diagrams are posted, it is very helpful (to me anyway) if they are sourced.

Thanks in advance.

MDT

What do you mean by sourced? The above diagrams are from AO SMith except the series install, I photoshoped it myself.

Thanks, it's helpful to know where to go for additional information.

Still can't find any of those via GOOGLE (though of course they many not be on-line).

Originally Posted by Michael Thomas

Thanks, it's helpful to know where to go for additional information.

Still can't find any of those via GOOGLE (though of course they many not be on-line).

Ah I see here is the tradtional parrall piping http://www.hotwater.com/lit/wiring/315268-000.pdf

And here is the first in last out piping.. well here is a couple differnt ones to show how this can work best even if there is three heaters involved.

Two unit first in last out http://www.hotwater.com/lit/piping/c...AOSCG61170.pdf

Three unit first in last out http://www.hotwater.com/lit/piping/c...AOSCG61280.pdf

Four unit first in last out http://www.hotwater.com/lit/piping/c...AOSCG61310.pdf

What is the benefit of multiple water heaters? Why not just install a larger heater? Just seems like a lot of extra work. In OP, it was a 75 gal and 40 gal installation. And the 40 gal was shut-off. Owner claims its there as a backup heater, then wouldn't it be best to hook up in series, not parallel for backup use?

Thanks, Ron, I always prefer to provide objective documentations of the opinions I present in reports.

Where you able to find those with a GOOGLE search, or did you know in advance where they were?

OK, I get now, a lot of this stuff is under Piping Diagrams , not Technical Bulletins, which is where I'm used to looking for such information at A. O. Smith Water Heaters.

Also, while I was there, I hunted up the AO Smith tech bulletin requiring use of the factory-supplied draft hood.

Originally Posted by Stanley Chow

What is the benefit of multiple water heaters? Why not just install a larger heater? Just seems like a lot of extra work. In OP, it was a 75 gal and 40 gal installation. And the 40 gal was shut-off. Owner claims its there as a backup heater, then wouldn't it be best to hook up in series, not parallel for backup use?

If they plumbed the two heaters in series, and had the one turned off it would just act as a storage tank, which is bad with out it having an aquastat and a recirculation pump so when the water cools it would get reheated. Unless the put the small heater as the first tank and still did not run it it would allow the water to warm up a little.

In parallel, you would have shut offs on the hot and cold of each tank so you can easily shut one tank off completely from the system. Which would be preferred since they do not have the tank running at all. A water heater that is not running and getting fresh water is a breading ground for bacteria. I would recommend that they either be piped in series and both tanks operate, or piped in the "First in Last Out" parallel and still both heaters up and running. Right now if the larger tank fails and they go to put the smaller tank into service, there is a chance of them getting seriously ill, or injured. The reason I added Injured is a water heater that has been out of service for some time can build up hydrogen in the tank, from the water reacting to the anode rod. This is not an issue during daily use since the hydrogen never gets a chance to build up.

The purpose of multiple tanks is to get the volume of hot water needed for the size of the home. In most cases you can use a 75 gallon heater in place of a pair of 50 gallon heaters, but the size can be a factor. Door ways may be to small, not enough space where the mechanical area is for the large tank, cost is also a factor Once you go larger than a 50 gallon heater the price more than doubles. Also recovery time a pair of 45K BTU 50 gallon water heaters will recover faster than a single 60K BTU 75 Gallon water heater.

Ron...any chance you can spend a minmute to eyeball the OP photos and tell me if the tanks are hooked up in series or parallel? Doors are wide, Owner has too much $$$ to burn, sale price of house is mega-bucks. Idon't see any good reason for a tandem hook-up. I am concerned about the health aspect of the backup heater.

Originally Posted by Stanley Chow

Ron...any chance you can spend a minmute to eyeball the OP photos and tell me if the tanks are hooked up in series or parallel?

I'm not Ron, but those are connected in parallel.

I don't see any good reason for a tandem hook-up.

With money to burn, it is likely: large tub; many baths; quicker recovery; all.

OK...Thanks Jerry. Enjoy the holiday.

Stanley,

The way to tell the difference is this way:
- parallel: the cold water feeds both water heaters, both water heaters hot out pipes connect to the hot water line
- series: the cold water feeds only one water heater, the hot out of that water heater feeds the cold in of the next water heater, and the hot out of that water heater connects to the hot water line

Got it...Thanks Jerry.

After my remarks below i wont go on with this posting, because until we have a definitive or commonly agreed diagram of a First-In Last-Out installation we cannot really have a clear discussion. No mfr. to my knowledge, uses the term or schematic FILO.

One last word from me would be that after searching the web and encountering other discussions ref. first-in last-out install's the only, insignificant, difference between FILO and Parallel install's that i've noticed, is that in FILO the final h/w tee is in a different position to the typical last h/w tee position in Parallel diagrams ( as in number one diagram above ).

Thank you all for the discussion, Ron in particular, i've learned much.

The drawings I posted are from A. O. Smith, they may not call it first in last out. But I was taught that by the master plumber that apprenticed me, and the teachers in the union halls call the piping First in Last out as well. It is only describing the lay out of the piping verse a equal balanced parallel piping where the pipes have to be the exact size, length and same fittings from the tee out to each heater.

Originally Posted by Ron Hasil

The drawings I posted are from A. O. Smith, they may not call it first in last out. But I was taught that by the master plumber that apprenticed me, and the teachers in the union halls call the piping First in Last out as well. It is only describing the lay out of the piping verse a equal balanced parallel piping where the pipes have to be the exact size, length and same fittings from the tee out to each heater.

Ron,

You will probably not encounter an installation that has everything equal due to physical site space requirements, and therefore the piping will not be equal in length. This may occur if the 2nd unit was installed at a later date and could not be placed into an ideal position to equalize the piping. However, even though the piping may not be equal lengths, if it fits the template for a parallel system---it's a parallel system.

Your sources were discussing the ideal installation, and rightly so for illustrative purposes, where everything can be equal and there is plenty of space to accomplish this task. However, in the real world.....

Rich

Originally Posted by Rich Goeken

Ron,

You will probably not encounter an installation that has everything equal due to physical site space requirements, and therefore the piping will not be equal in length. This may occur if the 2nd unit was installed at a later date and could not be placed into an ideal position to equalize the piping. However, even though the piping may not be equal lengths, if it fits the template for a parallel system---it's a parallel system.

Your sources were discussing the ideal installation, and rightly so for illustrative purposes, where everything can be equal and there is plenty of space to accomplish this task. However, in the real world.....

Rich

If you do not have the piping exactly equal, the system will not work what so ever. The heater with the shorter pipes will be doing all the work. As a plumber I have installed 1000's of water heaters in a balanced parallel system. In the real world we have to make sure it is installed perfectly so the heaters can work equally. I will dig up some pictures of installs to prove to you in the real world real plumbers can properly do a balanced parallel installation.

Here is one picture of a commercial install, I will post a residential install later.



If someone is in need of two water heaters to meet the demand of their home, I will explain to them that both heaters has to be same size and btu rating, and if there is not enough room to install two heaters side by side, then we have to look into other options.

IMO (and my opinion only) the best dual water heater setup is a heater with a coil installed and another heater that is a standard water heater. The heater with the coil has the hot and cold connected as normal. The other heater has the cold connected as normal and the hot connected to the inlet of the coil on the other heater. The outlet from the coil goes back to the cold on the heater without the coil with a small circulating pump installed.

Both of the heaters are controlled by their independent factory controls and the pump is controlled by a sensor in the tank with the coil. This way both heaters work the same and if one heater fails the other heater will still provide hot water to the house.

The heater with the coil feeds the hot water to the house. The other heater supples hot water to the coil only.

Originally Posted by Ron Hasil

I In the real world we have to make sure it is installed perfectly so the heaters can work equally. I will dig up some pictures of installs to prove to you in the real world real plumbers can properly do a balanced parallel installation.

Ron,

I agree with you wholeheartedly. I did not mean to imply that plumbers can't do a good balanced system----I have seen some great ones and the flow was equal as you indicated. But the reference that I was trying to make was to the photos beginning this thread. And they reinforce what you stated about the lengths should be equal. The arrangement can only be used as a stand-by as the lengths are different and the piping sizes are different.

Nice clean installation in your photo, by the way. Yours?

Rich

That one nope. Thats a union shop I know did that. I am never was smart enough in the past to take pictures of my work. But I will share some of mine in the near future.

The setup in my example requires no balancing as only one heater has water going to the house. But both heaters work equally.