any plumbers? (hot water heater issue)

We've got natural gas water heater (about 50 gallon) that I want to add another similar heater in series. I have no problem with adding a 't' into the black pipe for the gas, nor is there an issue with the water piping.

But the heater is in the attic, and is vented through the roof (straight up, about 6 feet). Can I tie the new heater's vent into the existing, or will another vent be required?

And no... I don't want to go tankless. Those are not all they are cracked up to be, and they are not compatible with a circulating pump we have either.

I really don't want to have to cut the roof for another vent...

Nonprofessional advice, the existing heater's exhaust piping was engineered for the proper draft. Doubling the exhaust amount without increasing the pipe size could prove to be problematic. Insufficient draft will lead to poison in the attic. So, the question is, how big to make the pipe after the junction? Problem now is, we're only guessing.

Nonprofessional advice, better to install a new, correctly engineered sized pipe than to increase the size of the existing one, only guessing what size it should be. Either way, you're going to need to cut the roof.

Check your local building code to insure the job is done properly.

~ Chance

I agree with Chauncey here... you need to account for BOTH water heaters venting at the same time where they tie together otherwise you could have the exhaust from one operating its burner backing into the other one and putting out its pilot light or even overheating the other heater which could be an unsafe issue. I'm guessing you may need a 5 inch pipe for them both or perhaps even a 6 inch pipe. There are tables to look up online for the purpose of calculating, here is a forum thread that talks about this subject in a little more detail.
http://www.doityourself.com/forum/water-heaters/185531-venting-dual-gas-water-heaters.html

Excel makes a tankless ventless water heater. Runs on NG or propane.
Recirculation systems won't effect the tankless systems.

http://excelonlinestore.zoeysite.co...pm-lpg-propane-ventfree-copper-heat-exchanger

the answer is no, cannot tie into existing vent.

people die after installing gas heat systems incorrectly. usually from CO poisoning

existing is in the upper most floor of a building ? risks are already at maximum

that new heater has to be 100% new install with separate everything

or dump it all and get one new bigger heater (with it's bigger chimney)

Got to find a roofer to mount a new vent. I do lots of things, but roof work on steep pitches is not one of them.

turbodog said:

Got to find a roofer to mount a new vent. I do lots of things, but roof work on steep pitches is not one of them.

Click to expand...

Good call. You're welcome.

~ Chance

turbodog said:

Got to find a roofer to mount a new vent. I do lots of things, but roof work on steep pitches is not one of them.

Click to expand...

I've put a new vent in a roof before and as long as you can manage on the roof it isn't that hard with some study on the right method beforehand and the right tools on hand too. The only issue I would consider problematic is if you happen to have power running in the attic in the ceiling area as cutting through the roof into electrical wiring could be just as dangerous as falling off the roof perhaps.

It's done.

And in this case, it is 1+1=3. Since #1 feeds #2, we picked up some efficiency from that.

I'm just $1800 poorer.

heater
vent
gas piping
drain piping
cold/hot water pipe modifications
expansion tank
overflow pan
bypass valves in case either heater fails

turbodog said:

It's done.

And in this case, it is 1+1=3. Since #1 feeds #2, we picked up some efficiency from that.

I'm just $1800 poorer.

heater
vent
gas piping
drain piping
cold/hot water pipe modifications
expansion tank
overflow pan
bypass valves in case either heater fails

Click to expand...

I've not seen this done with two big tanks but have seen the principle of it done in some large stores that I've helped with where they have a big 75 gallon (or 100 gallon even) water tank in the back for the meat/dairy/deli departments etc and restrooms up front of the store have a small inline 5-6 gallon electric water heater for more instant hot water hooked inline to the hot water tank in the back as the run was 150 feet which took a minute or three for hot water to arrive up front.

Typically gas water heater vents are only ~3-4".
I do agree with adding an additional separate roof penetrating exhaust vent. This is due to the short rise of the existing water heater, assuming it is the only appliance venting through that existing chimney/roof vent.
If the installation were within an existing large masonry chimney(~>13X9") it may have been possible to add a 3-4" Z-liner
through the existing larger dedicated chimney vent, to vent each separately. Many many decades ago it was possible to vent two gas appliances with a chimney large enough to allow proper venting. Those days are gone. Better off being safe, and add that addition roof vent for another heater, or upgrade/replace the existing hot water heater with one that is double sized 80 gallon using the existing roof vent. Wishing well, let us know what your plumber, city/town says to get You more hot water.
GL

When I moved into a house the gas water heater 3" vent had a 1" offset "sweep" about a foot long just above the tank. The guy from the gas company would not light it saying that was illegal. I lit it and installed a carbon monoxide monitor next to the heater and it never went off. Soon after the tank leaked and when it was replaced the sweep was removed. I kept the monitor though.

Anyway, my point is two heaters side by side would in no way be able to share one vent and meet code in my area. I see the op solved his issue but figured I'd add my experience.

When I moved into my home lol had no hot water morons before me installed thermostat but didn't attach it to tank. So a course it wasn't able to sense the temperature so it kept getting hotter and hotter till it destroyed heater element. Well that's how I assumed it failed since the thermostat was installed wrong. . I fixed it right and now have it set at my perfect shower temperature.

7 year old thread, I'll mention that heat pump water heaters can make a lot of sense for some applications. Some models are 120V now.