Help venting tankless heater/boiler?

[BowtieNut]

I'm just curious if anyone has some input for me about the vent pipe for my boiler. I'm new to this in-floor heat, and the cost is really starting to add up and make me wish I'd just done a Hot Dawg or Reznor setup. Anyways, here's my situation/problem.

My garage is 28' wide x 48' deep, and in the back is a separate "shed" room, 28' x 14'. On the wall that separates the two "rooms" is where I mounted the boiler (on the shed side). If you look at the picture, it's right on the opposite side of the wall from the big L-shaped bench in the corner. I was planning on running the vent pipe out the back wall of the garage (14' away), but according to the manual that came with the boiler (Takagi TK-jr tankless) I have to use 4" cat III single wall stainless vent pipe which is like $130 per 4' section. Dang that's going to be over $500 just for vent pipe!!!! And I don't think I can run it out the side wall since that will be right underneath the eaves.
Anyone have any suggestions? Just please don't tell me to move the boiler, since it's all plumbed and wired already, and that's right where the tubes come up out of the floor too. At this point I guess I'll just bite the bullet and vent it the way I planned rather than move it, but I was hoping maybe someone else here knows of another way I can do this without having to spend that much just for a stupid vent pipe. Any input is appreciated, thanks!!!!!

 

[HoosierBuddy]

1. Move it.

2. If not, shop for your best deal on vent pipe. Here's a link where they are selling it for half the price you quoted.

http://www.houseneeds.com/Shop/atop/subprod_cec.asp

I found that in 2 minutes. You can likely do better.

Good luck!

Phil

 

[Kinger]

You could vent out the side, but you would want the vent to be approx. 24" past the eve. Probably not appealing to the eye.

Why not go straight up through the roof?

 

[HoosierBuddy]

I've looked at it again and it's completely insane.

First of all, I had no idea that those instant water heaters requried a stainless Cat III vent. I just assumed you could use a standard B-vent. NOT! Then the prices! And, as you've seen, it's not just the straight lengths. It's also the terminator you need to mount outside the house. That's going to set you back another $75 to $100.

Hindsight is always 20-20 and I don't know what you paid for you tankless waterheater...but it makes me very thankful that my NTI wallboiler just needed 4" PVC to vent with. Of course, I hung it on an exterior wall...so that wouldn't have been a huge issue anyway. It cost maybe $20 for my vent!

My gosh...a $500 vent pipe. I never thought I'd see the day. The flue gasses must be too caustic for a regular b-vent and too hot for PVC. What a mess.

You need to take a look at moving it. How hard would it be? I hate going backwards too...but that stainless vent pipe is unfrickenbelievable.

Phil

 

[carguy123]

The reason you need the stainless pipe is the heat of the exhaust on the Tankless.

I am using the ventless tankless that mounts in the outside wall. They are selling them almost 4/1 just due to this issue.

 

[BowtieNut]

Thanks for the link Phil. That will definitely help. I searched for about an hour last night and found a couple other places that had close to the same price, but I couldn't find any better. But that's still way better than the price I was quoted locally.

I'll look into what my options are for going up thru the roof. It would definitely be a shorter run, but I don't know what kind of "special" pieces I might need. I think at this point moving the boiler is a last resort for me. I've been messing with this heat/plumbing/boiler stuff for almost a month now, and it's starting to get cold here in MN, and I just wanna get it done and get on to other projects in the garage.

From what I've heard, I think the vent material all comes down to the boiler efficiency. Anything over 90% can use the PVC vent, and anything below 90% has to use the stainless. Unfortunately mine is only 84%. Other than that I think it's a good unit for my garage. It was only $575, and it has modulating output from 20k to 140k BTU.

 

[W-Cummins]

I used the same unit in my shop as your installing. They are great, I must admit that they are over kill for a garage, but they are sure nice. The venting is rather $$$ you need to use the back flow preventer and then the adapter to the unit. Then you can run all the other sections as normal. I went out the wall ( my eves are way up there) and terminated my setup with the terminator "T" fitting. That setup works great. You MUST relocate the thermostat for the units heater to the outside in your location. If you don't do this in a cold place like you/we live you will freeze up the heat exchanger and dammage the unit.


William...

 

[HoosierBuddy]

It was only $575, and it has modulating output from 20k to 140k BTU.

The NTI Boiler is 92.7 % efficient, input is 20,000 to 150,000 BTU and it has an outdoor reset. It was almost $2300.

Phil

 

[BowtieNut]

William, thanks for the tip on the unit heater. Do I still need to do this if I have some RV antifreeze in the system? I'm not sure what temp my fluid is good to (I need a new tester, apparently mine doesn't work on the RV stuff. Even straight out of the bottle it wouldn't read anything). I just mixed it about 1:4 - AF:water so I'm sure it's not good down to -30 like my truck, but I figured it might be good enough if I keep the shop at 50 or so.

Or maybe it's just a good idea no matter what? Around here wouldn't that heater be running pretty much all winter then?


Wow! $2300. That sounds like a really nice unit, but I don't think I could have justified that much. Although eventually I guess it might have paid for itself at 92.7% > 84%.


Well, I finally got the gas hooked up to it Saturday, so now the only thing left is that dang gold-plated vent.

 

[W-Cummins]

Never mind Duuuuhhh... I didn't catch your using it to heat the floor, not hot water! If you use anti-freeze in the loops I don't see how it's going to freeze the heat exchanger as long as you have enough in the system. I would make sure that it's good for much colder than you might think it would get in there so it can take a flash of cold air in the unit. For your application you might want to wire the contacts for the thermostat closed so the electric heater will not turn on as long as you protect the heat exchanger with the antifreeze. I guess if you never let it get cold and run the anti-freeze in the system the heater would never turn on, and if you ever want to turn off the system for a long time (but kept the power to the tankless) it would just turn on if it got cold enough in the building and as the pump would not be running it would just keep the heat exchanger warm like it does when it's heating water ( not too much cost ).

I think I would give the engineers a call and see what they have to say. I called them a few time at the factory and they were very helpfull.


William....