Professional Tankless installation

[Bcyes]

Hi,
I am looking for some advice on my first time hot water tankless installation to look professional.
Here below is the illustration showing what I am thinking.
There are 2 existing vents to outside of the house above ground that I would like to use. However they are little large @ 6in and one of them is really down below close to the ground.
- Is there any problem to use a 6" to 2" reducer PVC mounted to existing sheet metal?
- Any issue if I use the very bottom vent for air intake? Will the air flow through like this?
Can I put one inline duct fan in the air intake just to make sure air coming in and up to the Tankless?

For the water part, can I use PEX tube (after the existing shut off valve) for cold and hot water?
For gas, the main supply is 1.5" I think and the soon to be removed old water tank use 1/2". I understand the tankless manual says must e 3/4". Can I just connect the flex hose to a very short run (1feet) of existing 1/2" pipe? The reason is the gas valve is after the 1feet long 1/2" pipe.

Any advice would be appreciated

 

[GReynolds929]

Not trying to be rude. You should hire a professional. there are too many safety concerns with what you’re asking to do it yourself. Besides most of the answers to your questions will be answered in the manufacturer’s installation instructions.

 

[SHEPLMBR]

If it is a condensating unit, I do not believe you can use existing b-vent. At a minimum, call the manufacturer.

 

[Bcyes]

Not trying to be rude. You should hire a professional. there are too many safety concerns with what you’re asking to do it yourself. Besides most of the answers to your questions will be answered in the manufacturer’s installation instructions.

May I know what kind of safety concerns with my setup?
Instruction says Direct vent, 2in PVC in and out. I would like to use my 2 existing vents for air in and out. There are already there without any use vs drilling another 2 holes through the wall. I hope that make sense.
I don't see any problem with the (upper) exhaust one, except it is bigger at 6in which I am not sure if using reducer 6 to 2in is ok. The (bottom) air intake is what concerns me, because it has a longer run and many turns. If that really a problem, can I add a inline fan to push the air?
I look at these 2 existing vents are just holes and if needed I can try to replace them with PVC if that matters

 

[Bcyes]

If it is a condensating unit, I do not believe you can use existing b-vent. At a minimum, call the manufacturer.

yes it is condensing unit. can you please let me know the reason why you don't think existing vents can be used for just air intake and exhaust, act as direct vent?

 

[CT18]

No No No. Those are not to be used as they are not air tight connections. You are dealing with dangerous off gassing that puts people in the grave. Where do those existing flue pipes go, up a chimney. You need to exhaust a tankless outside using the 2" pvc like the manufacture says. If you exceed a certain distance some manufactures require you to bump up to 3" pvc. Also need to know how many fittings you will use. Some manufactures make you change size if you exceed a certain number of bends.

 

[Bcyes]

No No No. Those are not to be used as they are not air tight connections. You are dealing with dangerous off gassing that puts people in the grave. Where do those existing flue pipes go, up a chimney. You need to exhaust a tankless outside using the 2" pvc like the manufacture says. If you exceed a certain distance some manufactures require you to bump up to 3" pvc. Also need to know how many fittings you will use. Some manufactures make you change size if you exceed a certain number of bends.

Those 2 existing vents are going right outside of the house on the other side. They are just like a 90 degree elbow.
Sorry maybe I didn't make it clear, the other side of the wall is outside of the house.

Ok, you are right, they might be not air tight as you said.
Can I use silicone to seal them ? Actually I assume I only need to seal the exhaust one, the air intake doesn't really matter?

I have very short distance for exhaust, 2in pvc should be fine according to the manual.

 

[SHEPLMBR]

yes it is condensing unit. can you please let me know the reason why you don't think existing vents can be used for just air intake and exhaust, act as direct vent?

Are you aware of what the term condensing means? Did you read the installation manual? You should be using a concentric exhaust kit

 

[Bcyes]

Are you aware of what the term condensing means? Did you read the installation manual? You should be using a concentric exhaust kit

what will be the different of my venting set up in terms of condensing?
I have a current 6in opening, when I use the concentric exhaust kit assuming 2in / 3in, what is the best wat to seal the gap?

Apart from my venting, any issue with my water and gas set up?

Thanks

 

[Jeff Handy]

Hire a pro, you will live longer.

 

[GReynolds929]

May I know what kind of safety concerns with my setup?
Instruction says Direct vent, 2in PVC in and out. I would like to use my 2 existing vents for air in and out. There are already there without any use vs drilling another 2 holes through the wall. I hope that make sense.
I don't see any problem with the (upper) exhaust one, except it is bigger at 6in which I am not sure if using reducer 6 to 2in is ok. The (bottom) air intake is what concerns me, because it has a longer run and many turns. If that really a problem, can I add a inline fan to push the air?
I look at these 2 existing vents are just holes and if needed I can try to replace them with PVC if that matters

You have no clue what you are doing and are going to be messing around with gas and carbon monoxide exhaust gases. Both of which if not installed properly will kill people.
You cannot use metal ducting on a condensing exhaust, it will rot out and leak carbon monoxide. Manufacturers are very specific about size and material used for their venting systems. They are specially engineered to work a specific way. You can’t just willy nilly use whatever is laying around because you don’t want to make the correct sized holes in the wall. You really should be hiring a plumber to do this install for you, that will be the best way to make it look professional.

 

[Mitchell-DIY-Guy]

Take the advice here, but more importantly READ THE INSTALLATION MANUAL!

Every gas appliance, especially water heaters of ANY kind (gas fireplaces, heaters, furnaces, etc.) have extremely specific and detailed instructions and options for venting. You DO NOT, under any circumstances, deviate from those. At best you’ll void the warranty or it won’t work properly. At worst we’ll hear about it on the evening news.

If you insist on using your existing B-vent, do NOT USE this condensing tankless. Get a conventional water heater.

 

[fixitron]

For venting, you might be able to use the B-vent as a sleeve for the PVC, but the exhaust must be at least 12" above grade or above the snow line.
The sizing of the gas line is not that simple. You have to take into account all of the other gas loads on the line coming into the house. The piping is all calculated based on how many BTUs/Hr of input to devices are needed for each leg, using the appropriate chart in NFPA 54 (National Fuel Gas Code). No you cannot tap into just a foot of 1/2" pipe because it would create an undesirable pressure drop to the water heater. Low gas pressure leads to high CO levels in the exhaust.
Hire a plumber with a gas license.

 

[havasu]

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[Mitchell-DIY-Guy]

This is a good time to remind all of our members that Plumbingforums.com, its owners, the volunteer admins, the volunteer mods and the professionals helping others on this forum are to be held harmless against any lawsuits which may arise from any action committed or omitted, which as a result may cause injury or death to any member or their family.

I don't know about that @havasu !! Everyone is telling him the same basic thing...follow the instructions or call a professional!

 

[havasu]

I hear you. I just trying to cover all bases.

 

[Bcyes]

Thank you all of your advice. I have learned a lot and would like to do it right.

I still would like to use the existing upper vent for 3in PVC air intake and exhaust. What is the best way to cover / seal the gap for this 6in hole with 2x 3in pvc in it ? is there any kit off the shelf I can use? or I have to custom make 2 plates to cover it?

For the gas, the main line is 1in, then there is a T from 1in to 1/2in. the 1/2in has about 12in long then to the shut off valve. That would mean the easier way is to connect my tankless after the shut off valve. Any problem when I connect 3/4in flex hose (around 4ft) from tankless to the shut off valve? Can I get away with that 12in long 1/2in which create little pressure drop?

 

[havasu]

The only way to verify is to hire a professional and conduct a manometer test.

 

[Bcyes]

absolutely no offense, but will not consider hiring a plumber for this job.
Like changing winter tires on a car could be very dangerous if not done by an official car dealer.
As I said, I would like to do it safely and hope to get advice on the proper way to do it.
Common sense I will be the only one taking full responsible

 

[Bcyes]

technical question :
the main 1in gas line is running 20ft from meter to a T. Right side of the T is 1/2" (12in long )to furnace. Left side also 1/2" (12in long) to water tank that going to be removed. These are the only 2 running gas, so BTU for sure enough.
as my pervious question, is it ok to leave that 12in long 1/2" pipe before the valve. And only connect a flex pipe 3/4" from valve to Tankless?
IF not, then I have to turn off main gas and switch that 12in long 1/2 pipe to 3/4". A lot of work and prefer not to mess too much on gas line. In this case, what is the best way to burn off the gas still in the pipe after main shut off?
Will gas furnace get damaged running without enough gas in the pipeline?