How to deal with the vents?


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Old 03-16-06, 01:25 PM
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How to deal with the vents?

Hello,

I am replacing two 50-gallon gas hot water heaters with a single gas tankless model that I recently purchased.

The Tankless unit product literature states that it has to have it's own dedicated venting system, and I am planning on installing it with a vent horizontal wall thimble to the outside of my home.


Question #1

The current 2 water heaters each have their own 3" diameter metal vents that both feed into a much thicker type B "master vent" that then goes straight to my roof and is vented to the outside. In addition, my homes gas forced hot air heating system also vents into this master vent. Once I remove the existing 50 gallon hot water heaters, I presume these hot water heater vents would need to be capped somehow. How do I do that?

Question #2

The tankless heater product literature says I need a dedicated vent, how come I couldn't just run a vent for this into the same "master vent" above instead of drilling through the wall of my house with the wall thimble?

See the picture below: The "Master Vent" in the house is type B and is at least 5" and maybe 6" in diameter. It does not go to a chimney but directly exits out the roof. The tankless system will have a 4" outlet and is classified as a category III device. The tankless system is a Paloma 7.4 gpm model. The installation manual for the tankless system is at:

http://www.homedepot.com/cmc_upload/...ee4ca3e401.pdf

Below is a picture of the existing setup.



The metal venting is type-B and is made by a company called metal-fab.

How come I can't join the tankless system into this existing type B venting after removing the hot water heaters?

Any help will be appreciated.
 

Last edited by jtward; 03-16-06 at 08:14 PM.
  #2  
Old 03-16-06, 07:50 PM
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Old 03-17-06, 07:17 AM
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Check with metalfab and the National Fuel Gas Code. I am not sure if you are allowed to cap horizonal and down facing flue legs. I would suggest removing the Tee in the main trunk.

The National Fuel Gas Code and the installation manual for your unit give very specific guidance about your flue. Your main trunk appears to be 5", so it is very unlikely you could add the BTU of a tankless to that. I can't get your document to load. If you have the Bosch 125 it requires a 5" vent, and you must follow the instructions regarding elbows and horizontal sections. If you have the Bosch 250, you may either use the available horizontal vent kit, or you must use STAINLESS STEEL vetical flue pipe.



UPDATE: OK, I got your manual loaded finally, and I see that you have a Rheem unit. The instructions are VERY clear that this must not be combined with other units on a vent pipe. There are reasons for this . Please read the National Fuel Gas Code.

Your unit DOES REQUIRE stainless steel flue pipe. All your existing trunks are galvanized B vent which is completely inadequate for your tankless unit.

Your unit may be horizontal or vertical venting, so I feel you can get this done. This is really a job for a professional contractor. If you do it yourself, be prepared for your building inspector to be very thorough. Improper venting of this unit can cause fire, CO poisoning ( DEATH ) and unsatisfactory performance of the unit.


This is an area where the box stores do a dsisservice to customers by failing to adequately advise them before the purchase about the unique and complicated installation requirements of tankless heaters. The only good thing going for you is the 1" available gas lines. Folks often but a tankless and then find they need to run a new gas main.
 
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Old 03-17-06, 08:23 AM
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Thanks for the great response. That is exactly what I needed to know. I will make sure it has a dedicated vent to the outside. I purchased the vent kit from the manufacturer and it actually seems pretty straightforward. The biggest problem I am going to have is making sure the termination point is 10 feet away from the fresh air intakes on the wall.
 
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Old 03-17-06, 10:37 AM
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The instructions say that I need to use a 3/4" gas line to the unit. what is the maximum distance I can I run the 3/4" line off of my main?
 
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Old 03-17-06, 08:01 PM
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20 feet for 0.3"WC drop // 30 feet for 0.5" WC drop
 
 

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