Water Heaters - Direct vent to traditional vent. Why Not?

We just installed a R75LSi (http://www.foreverhotwater.com/model-r75lsi.php). It replaced a gas 40 gal WH whose vent joined the vent from the gas boiler and the combined gas fumes went up the flu. On the R75LSi we start out with a direct vent then continue the exhaust part to existing system. A dip switch for the longer run has been set. The intake part(just over 5ft from the floor) remains open to collect the air from the area. Why would we not keep it set up like this? What is the best/worst case scenario? :mask:

Your link does not provide the full installation manual so MAYBE what you did is acceptable, but I doubt it.

What MIGHT happen is that when the furnace and the water heater are both firing you MAY not have enough chimney capacity. This MIGHT result in one or the other shutting down in a "blocked flue" fault. OR it might just start spilling carbon monoxide into the equipment room.

I'm pretty sure that you will have condensate problems in the existing vent system.

Did you do your homework BEFORE installation? Is your gas piping large enough to allow both the furnace AND the water heater to operate at full capacity? With a firing capacity of 180,000 BTUs the water heater is probably four or five times what the original tank-type heater would fire and possibly double the firing rate of your furnace.

You DID get a permit and inspection for this installation, didn't you?

The boiler is a Weil Mclain cga
We do have a carbon monoxide monitor
http://208.112.40.249/0710080910.jpg
From the picture, is our gas piping large enough to allow both the furnace AND the water heater to operate at full capacity?
How would we tell if our gas piping large enough to allow both the furnace AND the water heater to operate at full capacity?
Do home owners need to get permits to work on their own house?

I'm pretty sure you're kissing your manufacturer's warranty goodbye with this installation. Interior Rinnai's are designed with a coaxial intake/exhaust that draw and exhaust air from/to the outside directly. What you're describing is not a proper installation, but don't take my word for it-- call Rinnai and ask.

Additionally, I'm pretty sure you'll find it impossible to service the Rinnai with the installed pipe blocking its front cover.

Homeowners should want permits/inspections involved whenever Natural Gas piping and venting is involved. That's "level 2" plumbing.

Do home owners need to get permits to work on their own house?

It depends on the laws in your local jurisdiction but in most cases the answer is, yes. This is especially true when the job entails plumbing, electrical or structural changes.

I have no way of telling if your gas piping is sufficiently large from that picture. I would need to know the size of the pipe at the meter outlet and the entire length of the piping system, the number and type (elbows and tees) of fittings and all the appliances that the piping serves along with their BTU ratings.

I don't mean to be condescending but did you thoroughly read and understand the installation manual that came with the new heater? I am quite sure it explained in detail the necessary piping size for the fuel supply AND the venting requirements. Most residential gas piping is woefully inadequate for tankless water heaters.

Gas Piping
-Sizes are outer diameter

Out of the gas meter
90
35in of 1in dia
90
9in in dia
90
The previous was just installed by my utility company the day before my old water heater began to leak.
7ft of 1 ¼ in dia
90
4in of 1 ¼ in dia
90
52in of 1 ¼ in dia
T1(Boiler -Water Heater / Oven)

T1 To Boiler
Cut off valve
5 in of 1in dia
90
6 of 1in dia
90
42 of 1in dia
Sediment trap
CGA-5 Gas Boiler, Standing Pilot, 140,000 BTU



T1 To Water Heater / Oven
5ft of 1in dia
T2 (Water Heater - Oven)

T2 To Water Heater

3 in 7/8 dia
90
Cut off valve
10 in of 7/8 dia
90
10 in of 7/8 dia
90
42 in of 7/8 dia
Sediment trap
Water Heater Minimum / Maximum Gas Rate (Input BTU/Hr.) 15,000 - 180,000

T2 To Oven
4 ft in of 7/8 dia
Cut off valve
40ft?
Oven


Exhaust from boiler
6 ½
spill bell
6 in

Exhaust from Water Heater
3 in

When you say "direct vent" that implies a special system whereby the combustion air and the exhaust both pass through a coaxial flue pipe. You certainly cannot join that to any other flue. Your WH may have the option to direct vent or gravity vent. Two problems: (1) I suspect the instructions for your unit do not allow the vent to be shared in any case. (2) Most tankless require STAINLESS STEEL flue pipes. Your pictures look like galvanized.

(3) In almost any city in the US, a permit is required for this work.
(4) You are not giving us pipe sizes for the gas, just OD measurements?? but it looks too small. You must consult the National Fuel Gas Code to determine what size of pipe is necessary to support your 320,000 BTU.

I looked at the install brochure on line (http://www.foreverhotwater.com/documents/1110118.pdf) and I don't see any option for other than concentric venting. What you have is ALL WRONG. It also calls for minimum 3/4" gas supply, and the pipe I see in your picture looks like 1/2". And the 3/4 spec does not envision sharing with another 140,000 btu appliance.

Honestly, you need some help here.

I recommend you carefully study the manual for your tankless unit. I think you have several problems here.

After reviewing the pictures and specs all I can say here is "Hind sight is 20/20"

Next time I would do my research before installing everything incorrectly.:wall:

I echo what the others have written.

For the developed run of your gas piping you should have 1-1/4 inch nominal size piping from the meter as a bare minimum. You could reduce this to 1 inch or maybe 3/4 inch after the pipe tees off to the furnace.

In my opinion you have pretty much done everything incorrectly.

Sorry.