Homeowner installed tankless water heater. See photo

**Gene South** · 03-04-2013, 04:05 PM

Guys, The photo shows the flue for the original tank water heater on the roof. Below the roofline and protruding from the brick is the flue for the new tankless water heater. Not sure if this is a problem or not. Any thoughts?

Gene

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**Jim Robinson** · 03-04-2013, 04:50 PM

Not sure why they didn't use the original one. The manufacturer's instructions will tell you about the venting requirements for the new water heater.

**Galen L. Beasley** · 03-05-2013, 06:31 AM

Looks like a great place for a bird to build a nest. Also I dont think the soffit vent above it is a good idea.

**Dom D'Agostino** · 03-05-2013, 06:39 AM

It may be a direct vent model, but check the specs for that model as many have restrictions on the termination's proximity to soffits.

**Ron Hasil** · 03-05-2013, 07:08 AM

All makes and models of tankless heaters tell you not to use the venting that was used for a tank heater. Most of the non-condensingunits require a Stainless Steel venting. There is Rinnai that uses its own type of vent which is a concentric style, has the exhaust pipe ran through a plastic inlet air pipe. Condensing units allows for PVC to be used, and still is not allowed to use the old vent from tank heaters due to the condensation is very corrosive.

So if you see a tankless install using B-Vent, or just standard galvanized venting, it is a fail. I mentioned this in another thread a while back. Check the gas pipe size to the heaters, should be 3/4" or larger. Also do a BTU load calculation total, and check the meter to see if can handle the total BTU's. Many homes only have a 250K BTU meter. With the furnace, , stove/oven, and gas dryer, you are already well near 150K BTU, then you add a 199K BTU tankless heater, you all can do the math.

There should be some sort of screen on the end of the exhaust pipe.

**ted kidd** · 03-08-2013, 09:02 PM

What did the roof deck above the soffit vent look like? Signs of condensation?

**Larry Sparks** · 03-09-2013, 10:59 AM

Tankless water heaters require a larger vent than the conventional tank type heaters. The tankless usually require a minimum size of a 5 inch flue, therefore you cannot use the flue from the old heater. This is one of those issues the seller of the tankless units omit. The flue from the tankless being hotter than the conventional tank heater would require the vent to clear the roof by at least 3 feet to properly draft. I am not familiar with a high efficiency tankless unit that uses PVC for a Flue, but that may be the only exception. The new flue while hard to tell from a picture looks less than 5 inches.
I would write it up that it needs to be checked by a plumber profiecent in tankless units and fl;ue requirements. Disclaim disclaim disclaim

**Ron Hasil** · 03-30-2013, 04:55 PM

Originally Posted by Larry Sparks

Tankless water heaters require a larger vent than the conventional tank type heaters. The tankless usually require a minimum size of a 5 inch flue, therefore you cannot use the flue from the old heater. This is one of those issues the seller of the tankless units omit. The flue from the tankless being hotter than the conventional tank heater would require the vent to clear the roof by at least 3 feet to properly draft. I am not familiar with a high efficiency tankless unit that uses PVC for a Flue, but that may be the only exception. The new flue while hard to tell from a picture looks less than 5 inches.
I would write it up that it needs to be checked by a plumber profiecent in tankless units and fl;ue requirements. Disclaim disclaim disclaim

Sorry to say you are wrong, a tankless heater does not need to clear the roof by three feet. They can be vented out the side wall, as per the tankless manufactures instructions. All tankless heaters have a sealed combustion chamber with a blower for the exhaust, so there is no drafting. I would recommend calling your local distributer of a tankless heater (Noritz, Takagi, Rinnai) and take a installers course. This way you can put out proper and accurate information. Also since it is power vented, your statement of needing to be a 5" flue pipe is way off base as well. If it is not a condensing unit, the standard pipe is 4" unless you are using a Rinnai unit which uses a 5" pipe which is for fresh air intake and a 3" pipe inside the 5" pipe for the exhaust. I have been installing and servicing tankless heaters for well over 10 years now.

tom daley · 04-02-2013, 03:46 AM

Ron,
Thank you for your informative posts. I've just learned some things about Tankless that had previously puzzled me.

Tom

**Bob Harper** · 04-02-2013, 06:18 AM

As always, refer to the listed instructions for that appliance then if there are any local ordinances over and above that.

Tankless WHs are mechanically vented--not atmospherically vented. The venting must be suitable for positive vent pressure and listed for use with that appliance. See mfrs. specs.

The mfr. will spell out clearances to soffits and separation of intakes and exhaust

The mfr will spell out if screening a vent is allowed. Personally, I've never seen it cause a unit to fail from icing but I guess someone somewhere has. That's one reason the unit has a pressure switch to sense air movement. If the vent gets blocked by a bird's nest or ice on screening, the switch 'should' kick off the unit. Should. That's why every home should have an unlisted low level CO monitor outside the sleeping rooms and on each floor level.

Do not take Ron's advice about the gas pipe sizing lightly. Most I've seen were too small. Most I've seen dropped the static pressure in the house to where pilots sometimes dropped out on other appliances. The inlet pressure should be tested with the house under full load. If the pipes are still too small, you may be able to get the utility to jack the incoming pressure up enough. Otherwise, you may be looking at a 2 psi system.

**Mike Kleisch** · 04-02-2013, 06:57 AM

Originally Posted by Ron Hasil

There should be some sort of screen on the end of the exhaust pipe.

Would icing be an issue, or not so much on these types of units??? I get nervous seeing screens, I know some are allowed, but see small icicles once in awhile and thought screens would just make it worse.

**Ron Hasil** · 04-02-2013, 07:13 AM

Originally Posted by Mike Kleisch

Would icing be an issue, or not so much on these types of units??? I get nervous seeing screens, I know some are allowed, but see small icicles once in awhile and thought screens would just make it worse.

Never had an issue here in the Chicago area with icing. The manufactures recommend a screen on the end to prevent birds from nesting and such. Yes the heaters run the blower before igniting, and if it senses a blockage in the vent, or the fan it will not light up and send out an error code. Here is a link to an installers instructions. On page 13 they tell you it is required to install a bird screen.

http://www.noritz.com/commercial/fil..._NCC199-SV.pdf

**Mike Kleisch** · 04-02-2013, 07:27 AM

Originally Posted by Ron Hasil

Never had an issue here in the Chicago area with icing. The manufactures recommend a screen on the end to prevent birds from nesting and such. Yes the heaters run the blower before igniting, and if it senses a blockage in the vent, or the fan it will not light up and send out an error code. Here is a link to an installers instructions. On page 13 they tell you it is required to install a bird screen.

http://www.noritz.com/commercial/fil..._NCC199-SV.pdf

I was just wondering if icing has been an issue, as you addressed you have not seen any. I've only seen small icicles, but nothing even close to a blockage and wondered if anyone has seen a vent block up with ice?