Venting a Reznor 75K BTU unit heater.

[sdo]

I know this has been hashed and re-hashed. Building my detached garage and wanted to put a vent through the roof while the shingling was being done, in prep for a future heater. Went to a reputable HVAC contractor to get the venting components and discussed Reznor's requirement in their manual for UL 1738 compliant venting for Cat III appliances in residential applications. The contractor told me they have installed hundreds of these heaters and always use B-vent, and told me that's all I need. B-vent is listed as acceptable for vertical venting in the manual, but for commercial applications only. This is a detached garage, non-occupied structure, but still likely considered residential. The only double wall vent I could find on the market that is rated is Duravent Fas-n-seal W2. Forget that its expensive, I can't even find a good source to buy it. I can't use single wall stainless because it will route through an attic space. A local retail outlet that specializes in selling unit heaters sell vent kits for "Reznor heaters" for through-wall and vertical venting. I've figured out through photos on their website that the vent they are selling is actually for pellet stoves which is essentially a b-vent style double wall pipe, with stainless steel liner which is sealed with high temp silicone at all the seems and has a black painted galvanized outer wrap. So I called this place, talked to an individual that told me B-vent is not allowed, it must be stainless steel. I asked if the venting he sells and markets for Reznor heaters meets the UL 1738 standard and he said within the last month he got a letter stating it is suitable. I need to speak back with him to determine if Reznor provided this information, or the vent manufacture. What am I missing, why does this seem to be so difficult to get either a straight answer or the right venting that complies? What are my options to go through the roof?? Reznor UDAP 75

 

[TTA89]

If you need to get an inspection, I would try and talk to the inspector and see what he wants to see and go from there. The problem I find with *some* contractors is that they have installed "thousands of these" but they are not current on the latest codes, models, venting procedures so are doing it the way they have done for the past 20 years. You're just a "dumb" homeowner and don't know what you're talking about.

A concentric vent hit? I've never seen one of those....

 

[D45]

What does the heater's manual say?

My heater is a Hot Dawk 75K and it says to use 3" b-vent for vertical (roof) applications

The Duravent 3" b-vent also said that b-vent is for vertical residential applications

Here is my project thread, that started out as a 45K and recently was changed to a 75K

https://www.garagejournal.com/forum/showthread.php?t=325943

My 3" Duravent b-vent kit was under $70 shipped

 

[92nsx]

B vent with thimble in the wall, then straight out back wall.

 

[sdo]

Manual says for residential, needs to be UL 1738 compliant venting for Category 3 appliances. I did see Hot Dawg's manual shows B-vent for vertical. I asked my inspector and he said the manufacture's spec's prevail. Link below shows the vent I mentioned which I think is for pellet stoves.

www.djscompanies.com/reznor_udap_unit_heaters.html



The other funny comment the local contractor said when I asked him how he can get B-vent to pass on the Reznor heaters, he said they don't even get them inspected anymore because you can't comply. He made a comment that he did one job with stainless steel, and never again.

 

[thammel]

I did my reznor 60k udas with the stainless steel stuff - z-flex, I believe. It was really expensive and yes, was a pain to cut. Had to use a hacksaw and it was slow. I got the job done and it will last forever.

Tom

 

[bobbyjean]

This has come up alot on this site and i'm pretty new here.....
tta89-ouch buddy....i never considered any homeowner dumb
but i do consider the newer venting codes to be a kneejerk reaction to some DUMB contractor or homeowner who took no pride in there work and got someone hurt or worse....
Been doing hvac for a long time and the only thing i see with stainless venting is a seal of hi temp rubber at all seams...i have used the z-flex and it works well,they make telescoping sections -that may reduce the need to cut
Its very expensive vs. b-vent..... how bout b-vent with hi-temp silicone caulk at all seams?
Last thought-i like the 1 inch cl to combustibles with b-vent-don't try that with stainless-get your sawsall and hack on .

 

[Showkey]

In prior discussions “b vent” in horizontal applications was changed because it will not last as long as CAT III. The potential is rusting and then leaking CO in the building.

 

[bobbyjean]

The efficiency of the unit,the slope and length of the run will come into play for that,i just can't say i have ever seen b-vent rot or rust when installed properly...i have seen alot of leaks from chimney flashing on it though.
I guess if the unit isn't firing properly anything is possible-get those units serviced seasonally to avoid that

 

[Showkey]

The efficiency of the unit,the slope and length of the run will come into play for that,i just can't say i have ever seen b-vent rot or rust when installed properly...i have seen alot of leaks from chimney flashing on it though.
I guess if the unit isn't firing properly anything is possible-get those units serviced seasonally to avoid that

Very true but the manufacturers see a high and early failure rate of b vent in horizontal installs.........they are willing to accept that risk or high maintenance cost for inspections and early repairs. Should have taken a picture of my used b vent before replacement........thin as paper, rusting from the inside out, proper professional install, history of prior use unknown. After seeing mine the neighbor checked his ( house and shop built about the same time) his thump pushed through the pipe.

One issue that makes vent and heat exchanger rusting worse is setting garage temperature below 50*. The heater instructions specifically warn against low temp thermostat settings.

 

[90zcar]

Can someone explain why they say to vent upwards from the heater out? Doesn't make sense to me


Sent from my iPhone using Tapatalk

 

[D45]

Gravity to expel gasses..........so they rise?

1/4" per foot I believe