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I read this ad regarding a tankless water heater: The "direct" vent appliance allows for installation flexibility, saves valuable floor space and can be vented horizontally or vertically with no costly add-ons.

What's with the use of the word DIRECT? I thought a vent was a vent in that they all export gas fumes?
 

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I read this ad regarding a tankless water heater: The "direct" vent appliance allows for installation flexibility, saves valuable floor space and can be vented horizontally or vertically with no costly add-ons.

What's with the use of the word DIRECT? I thought a vent was a vent in that they all export gas fumes?

The higher BTU models are usually power vented. This allows for horizontal venting through a side wall. Traditional venting must be run vertically since it relies on heat rise to draw the exhaust fumes away.

While the venting for high btu models does allow for a lot of flexibility in placement, it adds significantly to the cost of installation. The sealed stainless steel vent pipe costs a small fortune.
 

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Often direct vented appliances of this type can be vented with PVC
I installed a whole house Quietside tankless water heater 125,000 BTU boiler in this manner. The high efficiency of the unit produces exhaust that is low temperature.
Basically direct vented means the exhaust and combustion air are both directly connected to the appliance so as to eliminate the necessity for additional ventilation requirements.
 

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Often direct vented appliances of this type can be vented with PVC
I installed a whole house Quietside tankless water heater 125,000 BTU boiler in this manner. The high efficiency of the unit produces exhaust that is low temperature.
Basically direct vented means the exhaust and combustion air are both directly connected to the appliance so as to eliminate the necessity for additional ventilation requirements.
How happy were you with this unit?

I've had three 185,000 btu units installed on projects and all three required the stainless vent pipe. In all three cases, these units only served the master bath. I just looked up the specs on the Quietside product as I'd never heard of that model before. I was surprised they could be vented with sched. 40.
 

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Last project we did we had a Bosch tankless installed (with s.s. vent) - works like a charm! Does the entire house. Can't remember the size of it, but I do remember it tops out at about 9 gpm. Worked well with what we installed - a Brizo shower system, but, we couldn't install a grohe shower system (with 6 outlets)
 

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I have recently taken a fancy to the Navien units. they vent up to 100 feet with 6 elbows and use PVC as the vent. You can also install several of these in a cascading arangement for extremely high water demand.
they cost about the same as a Bosch or Rinnai
 

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Carpe Diem
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I've been involved with 2 projects that had them. First was a Noritz. That needed 6' or 8' of Cat III pipe and then could tap into the furnace flue. HO's love it. Can run the dishwasher and 2 showers without loss.

Recently saw a Rheem installed. That one needed Cat III for the entire run. The venting was expensive. It was the same BTU (199,900 I think) but didn't seem quite as efficient as the Noritz.

A friend of mine had some off-brand installed and like it a lot. Was in AZ so was installed in garage but had a built in blower so no special vent needed. I would be afraid of maintenance with an off-brand. How accessible are spare part and what are the service costs?
 

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I've been involved with 2 projects that had them. First was a Noritz. That needed 6' or 8' of Cat III pipe and then could tap into the furnace flue. HO's love it. Can run the dishwasher and 2 showers without loss.

Recently saw a Rheem installed. That one needed Cat III for the entire run. The venting was expensive. It was the same BTU (199,900 I think) but didn't seem quite as efficient as the Noritz.

A friend of mine had some off-brand installed and like it a lot. Was in AZ so was installed in garage but had a built in blower so no special vent needed. I would be afraid of maintenance with an off-brand. How accessible are spare part and what are the service costs?
Tapping that Noritz tankless water heater into the furnace vent pipe should NOT have been done. That did not meet code.:whistling
 

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Carpe Diem
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Tapping that Noritz tankless water heater into the furnace vent pipe should NOT have been done. That did not meet code.:whistling
It did at the time. This was back in 2004, Kendall Co, Il., new construction.
I was recently at that house and the plumbing pass sticker was still on the basement wall.
 

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It did at the time. This was back in 2004, Kendall Co, Il., new construction.
I was recently at that house and the plumbing pass sticker was still on the basement wall.
Then the inspector didn't do his job. Just because it passed inspection doesn't mean it was installed to code or should have been installed that way or been passed. Its an improper install and should be corrected.:rolleyes:
 

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ChrWright, it's a QVM9 I've had some minor issues with the unit but overall it's been reliable. The building has 2400 lft hydronic floor tubes on two zones plus a second floor zone with base board (one room) 2 bath.
I installed a converted electric water heater for extra h/w storage. Our water is very cold coming out of the ground but it seems to manage the requirements well.
 

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Then the inspector didn't do his job. Just because it passed inspection doesn't mean it was installed to code or should have been installed that way or been passed. Its an improper install and should be corrected.:rolleyes:
Don't preach to me. I didn't install it. Preach to the architect, HVAC designer, union plumber or county building inspector that were involved with it. I was just there to install tile after the customer moved in. :rolleyes:
 

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Then the inspector didn't do his job. Just because it passed inspection doesn't mean it was installed to code or should have been installed that way or been passed. Its an improper install and should be corrected.:rolleyes:

I am curious....so aside from the code violation, what is the actual, definitive reason for not allowing it? Is it reasoned that the flue pipe would allow the exhaust to "fall" back?
 

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I am curious....so aside from the code violation, what is the actual, definitive reason for not allowing it? Is it reasoned that the flue pipe would allow the exhaust to "fall" back?
"Forced" would be the word I would use. The tankless unit is power vented. The manufacturer does not allow this way of venting either. Its STRICTLY PROHIBITED.
 

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We have installed only one in a new home, and it was wall vented. I always ask when I want to know....sometimes it is obvious, sometimes....well, the codes have been wrong before.
 

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Newer and more efficient units put less heat out the flue pipe and so you can avoid using stainless steel and save on your utility bills. With stainless a 3" pipe will take a 6" hole in the wall for the Noritz thimble which makes for bigger hole in the wall. For stucco walls we use a Universal TCT hole cutter that makes a neat hole in the stucco and also cuts through the OSB sheathing - faster and cleaner than line drilling and no chance of cracking the stucco accidentally.

For hand sinks an alternative to running a gas supply is to use an electric 110 or 220 volt version. These are to minimize use of the main hot water tank by heating the water where it will be used and are a much less expensive alternative much of the time to a new central tankless system where you may never see a payback and have to deal with potential installation problems.
 
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