The tankless water heater vent pipe had a B vent at the top of the unit and then went into the existing A vent up through the roof. The connection does not seem to be proper, am I correct?20210301_1345441|690x388
Do you have a zoomed out picture where we can see all of the vent?
What is A vent?
What is the model of the water heater?
The installation in your picture appears to have been executed by a DIY’er.
Sorry, I forgot to attach, the photo of the whole vent pipe is now attached.
I am kinda of with you on the DIY’er. The model is a Takagi.
Takagi is a brand. Do you have the model? did you look at the vent in the attic? how did it look at the roof? you have a b-vent to b-vent reducer going into a single wall… so the adapter is not really designed for this purpose. Single wall vent cannot penetrate the ceiling, it has to be a b-vent. I cannot see this in the pic.
Model T-KJR2-IN
I just found that, Simon…speedy.
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Just keeping you on your toes, Larry 
That whole install is messed up and needs to be checked in its entirety.
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Thank you. It just didn’t look right.
No way. The entire flue pipe is just adjustable elbows and it looks like it is just stuck into that first small section of B-vent directly on top of the unit.
Simon,
I just read this yesterday on the Gas Furnaces page (near the bottom quarter of the page):
Type A Chimneys
Type A chimneys are low-heat, prefabricated metal chimneys. They have been tested and approved by the Underwriters Laboratories.
EDIT:
Class A Insulated Stainless Steel Chimney Pipe is a UL Listed multi-fuel system and is ideal for venting residential appliances, burning natural and LP gas, #2 oil, and wood. It has been specifically designed for today’s modern high efficiency wood stoves, wood burning heaters, and for combination fuels in central heating systems. UL103 Standard for safety factory-built chimneys for residential type and building heating appliances
Sometimes referred to as “Triple Wall” chimney pipe, most factory built chimney pipes are now double wall chimney pipe with an insulation pack between the two. Some codes still require a triple wall chimney. The triple wall chimneys of today have an insulation pack between the inner layers and an airspace between the outer. In either case they are generally considered “Class A” chimneys used for high-temperature exhaust gasses from common solid fuels such as: Wood, Oil, Coal, and other high-output fuels. The main advantage of using Class A insulated chimney pipe is the reduction of creosote because the inner-most layer of the pipe gets hot quickly and stays hot throughout the burn (see FAQ’s for importance of insulation). It also creates a better draft and therefore more efficient results from the appliance, and reduces clearances to combustible materials around it. Some models still use a triple wall design but now use the insulation between the two innermost layers to achieve a similar result.
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Saman,
Class A vents are not low-heat. Find a better source. The reason I asked is because there was no class A vents in the picture. I think the OP made some sort of a typo or some such.
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Simon,
It does look like InterNACHI has incorrect info listed… I looked around and you’re right, Class A is not designed for low heat. I sent an email to InterNACHI. Hopefully, they’ll correct the training material.
Thanks for the info!
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Good luck on that… … …
Are they trying to say the vent itself would be low heat so it has less of a clearance requirement from combustibles?
Single wall vent requires 6" min. clearance to combustibles and must transition to B or double wall vent at the ceiling and continue as B-vent to the exhaust point with 1" min. clearance to combustibles.