Hi everyone,

I haven't been in the game too long (two years), but I have been in a few hundred houses. I have never seen a DHW exhaust like this in any house. There is no draft diverter at the top of the water heater, and the exhaust is continuous until it enters the chimney. It is commonly vented with the 80% efficient furnace.

I asked the owner about it, and she said she would have it checked into. Once she got back to me, she said the HVAC company she has on contract (this is a rental unit) said that the metal box in the middle of the picture is the draft diverter.

So, first, is that really a draft diverter? Second, if so, how does it work? I can only figure it's a valve of some sort. When or where can I expect to see this technology in the future?

Thanks in advance for all your feedback and advice.

Views: 1338

Reply to This

Replies to This Discussion

I was back in the residence today and took a look at the underside of the box in question. It is most certainly a draft diverter, but it looks as if it is decidedly unsafe. Based on the stack effect, the warm, moist air would circulate at the top of the box and cause the box to rust. I took a picture, and lo and behold that's exactly what's happening. I assume the box will eventually rust out, and the diverter will fail or the box will be compromised.

The primary purpose of a draft hood is to maintain a constant, and not excessive, draft from the appliance, much like the barometric damper on a furnace flue.

In many jurisdictions, you can't vent a gas appliance into the same flue used by any non-gas combustion appliance and the smaller BTU/hr burner must enter below the larger burner if two gas units share a common chimney.

Also, a large chimney flue may not generate enough draft speed to properly evacuate the water heater gasses, which may be why there is moisture accumulation in that intermediate draft hood, which is also far enough from the water heater to allow flue gasses to cool. The long horizontal run and the number of elbows will also significantly slow the flue gas speed.

I would recommend a complete rebuild of that flue system, using B-vent directly to the outside, with a proper draft hood at the water heater.

I am by no means an expert in this area & you should call one in to look at it but the applicable code is:

IRC 2009 - G2407.3 (304.3) Draft hood/regulator location. Where used, a draft hood or a barometric draft regulator shall be installed in the same room or enclosure as the appliance served so as to prevent any difference in pressure between the hood or regulator and the combustion air supply.

As for seeing this "technology" in the future - lets hope not as atmosperic devices should be going bye bye & replaced with direct vent

You also have to recall that a draft hoods main purpose is not to ensure a draft but to act as a safety feature in case the vent is blocked by allowing the gasses to escape into the room - Safety Sunday: Water Heaters, the Combustion Process & the Draf...

So, if I'm reading that correctly, as long as there is no pressure differential between the combustion air supply and draft hood, it is technically in compliance. The combustion air intake and draft hood are in the same room.

As far as "future," I meant in other houses, not as new units are installed, of course. I would be stunned to see something this silly in new installation.

Have you done any CAZ testing under worst case situations to test for combustion gas spillage? I agree that this horizontal venting holds a lot of potential for dangerous CO spillage. What are the rise, run and sizes of the flue pipes, including where and size of the flue the DWH is tied into?

Looks almost perfectly horizontal.  Think they took a level to it (lol)?

Strangely, it does slope within normal limits. I hadn't thought about flue gas condensation being a problem, though. On the plus side, there are a handful of CO detectors around the house.

The next step will be a full CAZ. Having not identified the box as the draft diverter, I didn't have a chance to do so.


It might be a direct vent mobile home water heater installed in a house. This is only a guess but check underneath the water heater and look for a opening.


Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.  Home Energy Pros is sponsored by the Better Buildings Residential Network.

Latest Activity

Dennis Heidner replied to Rod Fox's discussion Utility Meter Accuracy
"For Rod, second part... When I see really large electric services... my first reaction my be…"
2 hours ago
Dennis Heidner replied to Rod Fox's discussion Utility Meter Accuracy
"Rod,  I did see earlier that you had calculated the loads.  The key is even though a…"
3 hours ago
Grzegorz is now a member of Home Energy Pros
8 hours ago
Rod Fox replied to Rod Fox's discussion Utility Meter Accuracy
"Dennis, that's a ton of useful info and it will take me a bit to fully assimilate those…"
8 hours ago
Ben Haas replied to Rod Fox's discussion Utility Meter Accuracy
"Yup..... 1200 amp service to the compound.....  3 -400 amp panels, all single phase since 3…"
20 hours ago
Walter Ahlgrim replied to Rod Fox's discussion Utility Meter Accuracy
"The more I think about it if the problem cannot be the current transformers reading small loads,…"
Dennis Heidner replied to Rod Fox's discussion Utility Meter Accuracy
"Note to readers 0.5A instead of 5A for reading with A/D.... the edit to correct that didn't…"
Dennis Heidner replied to Rod Fox's discussion Utility Meter Accuracy
"Rod, I have some of the CT's that you referenced in the openenergymonitor system.  They…"

© 2015   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service