Horizontal B-Vent Unit Heater Question

[bagsanthony]

Just had a Hot Dawg 75K unit heater installed. Unit has a power exhaust. My HVAC buddy put it in…. One question, he put a thimble on the interior side where it contacts the drywall but do not see one on the exterior? Is this correct or should there be one? He put high temp fire caulk around the exterior penetration. Feedback appreciated. See pics below

 

[fitter30]

Horizontal flue needs cat 3 stainless flue not B vent. Page 6

https://www.google.com/url?q=https://www.modinehvac.com/wp-content/uploads/2020/01/Hot-Dawg-Power-Vented.pdf&sa=U&ved=2ahUKEwjxjNjzmNeRAxXAnokEHaoCJIAQFnoECAUQAg&usg=AOvVaw0h9K8YybFhVWNObsu-igV-

 

[shaggyant]

Horizontal flue needs cat 3 stainless flue not B vent. Page 6

https://www.google.com/url?q=https://www.modinehvac.com/wp-content/uploads/2020/01/Hot-Dawg-Power-Vented.pdf&sa=U&ved=2ahUKEwjxjNjzmNeRAxXAnokEHaoCJIAQFnoECAUQAg&usg=AOvVaw0h9K8YybFhVWNObsu-igV-

 

[allinon72]

This is one of those hot button topics where code clashes with practicality. First, is stainless horizontal vent pipe required in some jurisdictions - yes. Should it be used in longer horizontal runs - probably. Are there thousands of short, horizontal runs of regular b-vent piping installed on heaters all across the country - yes. Can't tell from your pics but looks like a short run.

Another topic point is, is this installation being inspected? My guess is no. Therefore, are there any immediate safety concerns with that installation? In my opinion, no.

Around here a thimble would not be used on the exterior side. If it could be made to fit around the ridges of the metal it would be extremely ugly. I see nothing wrong with that installation, both safety or practicality wise.

 

[PoorUB]

Stainless isn't required by the jurisdiction, but by the manufacturer! Stainless is required on a horizontal vent every where. The jurisdiction requires the 7nit to be installed as required by the manufacturer.
Now, I do agree there are millions of these heaters installed with B-vent. Less than ten years ago B-vent was approved. But that doesn't make it right today.

B-vent will work fine, but you might be replacing it in a few years, perhaps as soon as 3-4 years. It rots out the inside liner.

 

[PoorUB]

Just had a Hot Dawg 75K unit heater installed. Unit has a power exhaust. My HVAC buddy put it in…. One question, he put a thimble on the interior side where it contacts the drywall but do not see one on the exterior? Is this correct or should there be one? He put high temp fire caulk around the exterior penetration. Feedback appreciated. See pics below

What type of insulation is in the wall. Correct or not, B-vent needs 1" clearance to combustible. Where I am at the inspector would fail it and require a thimble to insure nothing crosses that 1" of clearance.

 

[The Cobbler]

my heater manual clearly stated for horizontal run a stainless flue was required. period. the cost of that compared to my reluctance to have a roof penetration made me easily decide to run it thru the shingled roof .
would B vent work without issue? Probably... would I have gotten a pass on inspection? maybe, probably not. would I risk not getting an inspection? nope

 

[finn]

Stainless isn't required by the jurisdiction, but by the manufacturer! Stainless is required on a horizontal vent every where. The jurisdiction requires the 7nit to be installed as required by the manufacturer.
Now, I do agree there are millions of these heaters installed with B-vent. Less than ten years ago B-vent was approved. But that doesn't make it right today.

B-vent will work fine, but you might be replacing it in a few years, perhaps as soon as 3-4 years. It rots out the inside liner.

I recall that prior to some year, which I don’t remember, B vent was approved. At some point that changed and now it’s stainless.

There was a big debate on this site when the change was made.

i remember this because I installed two of the same heaters in different buildings a couple of years apart. One called for B vent with stainless optional, the other, later installation was stainless only.

 

[bagsanthony]

What type of insulation is in the wall. Correct or not, B-vent needs 1" clearance to combustible. Where I am at the inspector would fail it and require a thimble to insure nothing crosses that 1" of clearance.

I purposely left the area around the exhaust with no insulation. The rest of the wall is insulated. The exhaust punches through the drywall with a thimble and then the metal pole barn wall.

 

[Bert_]

B-vent will work fine, but you might be replacing it in a few years, perhaps as soon as 3-4 years. It rots out the inside liner.

Little exaggerated. Tons of horizontal exhaust b-vent installs that are 20 years old and in fine shape.

In the electrical shop I have a 100,000 tube heater. The guy who installed it the first time put in way to long of a tube for the size of burner. The exhaust was condensing so much I had a 5 gal bucket inside the shop to catch the drips! After 8 years or so it was rotting out the clamps that connect the tube together and the tube was thin in a few spots. B-vent going out the wall was definitely not new anymore but mostly fine. Clearly the the b vent was not the weak link

A couple years ago I redid it with about half the length of tube and the proper baffles. Yes I used b vent to exhaust through the wall again. I expect this time it will last the life of the heater.

 

[fitter30]

Flue gas is corrosive as the condensate galvanized doesn't hold up. Manufacturers have to follow code just for the liability and your safety. Your going to do wat you want. Drop dead tomorrow house gets sold and 5 years after the install new owners die from Co poisoning or you get sick.

 

[PoorUB]

Little exaggerated. Tons of horizontal exhaust b-vent installs that are 20 years old and in fine shape.

When I did HVAC service, I can't tell you the number of times I replaced B-vent on shop heaters in less than five years. From my experience it won't last ten years. I can see why manufacturers require stainless. I replace the vertical venting on my shop heat in less than ten years. I should just put in stainless.

 

[PoorUB]

I recall that prior to some year, which I don’t remember, B vent was approved. At some point that changed and now it’s stainless.

There was a big debate on this site when the change was made.

i remember this because I installed two of the same heaters in different buildings a couple of years apart. One called for B vent with stainless optional, the other, later installation was stainless only.

I sold Modine unit heaters at a wholesaler. I would guess about 2015 Reznor required stainless. It was a great year for Modine as they had not made the change. A year or two later Modine required stainless.

 

[Mr onetwo]

You could have used the proper Tjernlund vent hood to get clearances thru the wall....very common up here.

 

[danski0224]

Flue gas is corrosive as the condensate galvanized doesn't hold up

The inner liner of Type B vent is aluminum.

And yes, it will corrode.

 

[danski0224]

This is one of those hot button topics where code clashes with practicality. First, is stainless horizontal vent pipe required in some jurisdictions - yes.

It is required by the manufacturer.

Should it be used in longer horizontal runs - probably. Are there thousands of short, horizontal runs of regular b-vent piping installed on heaters all across the country - yes. Can't tell from your pics but looks like a short run.

Short or long, it doesn't matter.

Another topic point is, is this installation being inspected? My guess is no.

Doesn't matter, it should be installed per manufacturer specification.

Therefore, are there any immediate safety concerns with that installation?

"Inspected" doesn't necessarily mean "installed right".

The immediate safety concern is that the equipment is not installed per manufacturer specifications.

In my opinion, no.

This reasoning works, until it doesn't.

Around here a thimble would not be used on the exterior side. If it could be made to fit around the ridges of the metal it would be extremely ugly. I see nothing wrong with that installation, both safety or practicality wise.

The wall penetration flashing detail is wrong, relies on caulking to seal it, and will eventually leak.

 

[danski0224]

Just had a Hot Dawg 75K unit heater installed. Unit has a power exhaust. My HVAC buddy put it in…. One question, he put a thimble on the interior side where it contacts the drywall but do not see one on the exterior? Is this correct or should there be one? He put high temp fire caulk around the exterior penetration. Feedback appreciated. See pics below

That is not a thimble on the inside.

That is a support plate, it works like a Chinese finger toy. The vent pipe cannot be easily pushed inside from outside. At least until the screws/anchors pop out of the drywall.

This is a Type B vent thimble (which also needs to be visible when installed):


Your HVAC buddy did not install it properly.

Type B vent is not allowed for horizontal installations, and I am reasonably sure that this stipulation pre-dated the rule change in unit heater installation instructions.

Your equipment does not have a "power exhaust", it has a draft inducer. It pulls the gases through the heat exchanger. If you stuck a manometer in the flue pipe, it will read a negative pressure. It is not a minor technicality.

The only allowable installation for Type B vent in a horizontal configuration requires a power venter like a Field Controls SWG series, which will require a controls package and a barometric relief damper. And then you will get into makeup air issues.

Feedback: Not installed properly.

Just because there may be other similar installations does not make it right. Because it is not installed properly, you are assuming a great deal of potential risk.

The equipment safeties cannot detect a rotted out flue pipe, and the equipment will therefore continue to operate.

 

[allinon72]

I reference my post above and enter into the record, "Exhibit A"

 

[fitter30]

If aluminum liner was code they wouldn't spec cat 3 stainless. 80% furnace keeps the water vapor in the vapor state but some must condensed in the horizontal towards bottom of the pipe and it's acidic.

 

[bagsanthony]

Well geez look what I just started lol

 

[Jackfre]

If the manuf says it is ok, it still isn’t practically. It is cheapest and the only reason it was pushed through any approval agency was for cost reduction purposes. Having been on an NFPA committee we saw a lot of this. I also represented Selkirk, Dura-vent, Z-Flex, Tjernlund and other venting products over a 30 yr career after 25 working with the tools and there have been vast changes in materials typically increasing in cost to satisfy the technical needs of the higher efficiency equipment. Your B-vent is in. IMO it is unfortunate but let me ask, which way is the pipe going to drain the condensate? If to the heater do you have a drain there? If to the outside watch the finish on your metal siding. Also is the seam on the pipe at the top? With the exception of the choice of material your install looks pretty clean. You will likely have to maintain the exterior caulk as expansion and contraction do what they do and you are certainly forwarded to keep an eye on the system drips and rust showing. Happy Heating!

 

[bagsanthony]

If the manuf says it is ok, it still isn’t practically. It is cheapest and the only reason it was pushed through any approval agency was for cost reduction purposes. Having been on an NFPA committee we saw a lot of this. I also represented Selkirk, Dura-vent, Z-Flex, Tjernlund and other venting products over a 30 yr career after 25 working with the tools and there have been vast changes in materials typically increasing in cost to satisfy the technical needs of the higher efficiency equipment. Your B-vent is in. IMO it is unfortunate but let me ask, which way is the pipe going to drain the condensate? If to the heater do you have a drain there? If to the outside watch the finish on your metal siding. Also is the seam on the pipe at the top? With the exception of the choice of material your install looks pretty clean. You will likely have to maintain the exterior caulk as expansion and contraction do what they do and you are certainly forwarded to keep an eye on the system drips and rust showing. Happy Heating!

We’re not opposed to swapping out to CAT III stainless… just weighing out if it’s fully necessary

 

[PCustoms]

We’re not opposed to swapping out to CAT III stainless… just weighing out if it’s fully necessary

Yes, it is.

 

[Bert_]

We’re not opposed to swapping out to CAT III stainless… just weighing out if it’s fully necessary

It's already there. As long as it meets clearances, then wait and see IF it rots out, replace it then.

 

[danski0224]

We’re not opposed to swapping out to CAT III stainless… just weighing out if it’s fully necessary

There are many things wrong with the venting and wall penetration details.

Good luck.

 

[bagsanthony]

There are many things wrong with the venting and wall penetration details.

Good luck.

Thanks.