Duct Question

[Musicphan]

Hi Everyone,

I'm going through the agony of finding a reliable contractor to install the duct work on my roaster. WOW - what a flaky industry.

Per USRC the required ducting needs to be 6" double walled Class A duct work. When I contacted USRC I found out the internal wall needs to be stainless as well. Here is where we are getting hung up on - when we look at the positive pressure duct work it gets REAL expensive $250-300 per 4'... standard non-positive pressure duct work is about $90 per 4'. Can anyone confirm if positive pressure is required? What if use non-positive pressure in roaster install?

Any help would be appreciated...

Mike

 

[Mr.Peaberry]

Hi Mike,

I believe that positive pressure ductwork is going to be code for the type of installation. You don't want airflow coming back into the building through the ductwork when the roaster is not on. Having said that...I'm wondering if there is a way to rig a switch to open and close a damper as required...and if that would satisfy code. Of course that may be more expensive in the long run, as the positive pressure ducting is a passive system. If it were me, I'd check for architectural salvage/surplus to see if you can find some slightly used ducting for the install. Best of luck.

Peaberry

 

[sae]

Positive pressure is the way to go because you are pushing air up from the fan, therefore creating positive pressure in the pipe - as opposed to negative pressure that's created from a draft chimney on a fireplace. I get nervous when I see people using thin single walled spiral wrap ducting. That's a risk I'm not willing to take!

The stainless on the inside is so the pipe stays cleaner longer and is easier to clean.

It's really expensive. I think I paid about $125/ft installed.

 

[Musicphan]

When I look at both the positive pressure and natural venting they LOOK identical... there doesn't appear to be any type of damper to prevent backflow. However, I'll have my HVAC guy look into that as well. I'm wondering if there is a different gauge stainless used on the Positive Pressure.

 

[Mr.Peaberry]

I don't think there is any difference in the construction of the pipe...so it is misleading calling it "positive pressure' ducting. I believe it is a positive pressure HVAC "system" so that the airflow out of the room exits through this ducting. The 304 stainless steel is used in the 1000 F ducting and the 400 F ducting uses galvanized exterior and aluminum interior. In any event, I think the expense is unavoidable, but the positive pressure system is not the reason for the expense, it is the materials used at the high temps.

 

[sae]

It has nothing to do with a damper. Draft chimneys (fireplaces, etc) are a great example of negative pressure systems as they PULL air through the chimney so there is negative pressure inside the pipe which sucks air into the chimney if there is a leak somewhere. A positive pressure system PUSHES air through the chimney so if there is a leak somewhere the smoke will want to escape the chimney.

The positive pressure systems are tested and rated to be able to withstand a certain amount of positive pressure inside the chimney and the joints between the pipes are also designed to contain this pressure.

 

[mbristol22]

how long of a run are you making? I have seen double wall b-vent used for installation. You also want to have maintenance in mind when you do this installation. The pipe will need to be cleaned periodically. Installation can become expensive though.

 

[Musicphan]

We went with the Serlick IPS product after much debate... its expensive as hell. What I discovered is the IPS product (and DuraVent has a DuraStack product which is similar) has a much thicker inner wall. Better for fire containment... they also are designed for positive pressure venting. The IPS product has a inner ring which connect the two pieces of duct together - then a secondary outer band for rigidity. Material cost alone were close to $2K - that was 12' of duct, a T connector and cap for easy cleanout, flashing, storm collar and rain cap. Installation is going to cost me about $500 labor.

 

[Mr.Peaberry]

That is some expensive pipe Musicphan! Thanks for posting...sounds like the contractor treated you fairly on the install!

 

[MillCityRoasters]

Your coffee roaster is a a "Class III" appliance that technically requires positive pressure exhaust. That doesn't mean Class A double walled. Single walled class III vent is available.

Class A is double walled stainless and only stainless inside for corrosion resistance, not cleaning. The thinking is that condensation can corrode the inner aluminum liner of class b (aluminum inner, galvanized outer).

As a practical matter, class b is rated to over 400F and the exhaust out of your chaff collector is typically no more than 300F. You're burning clean blue flame natural gas and your exhaust volume is typically minimal. For these reasons, guys often get away with class b.

Obviously, the risk of a chaff fire is always an issue. I'd suggest you do enough maintenance and cleaning to ensure you don't have one.

 

[Millattus]

The most important task solved in the design of modern houses is the creation of an effective supply and exhaust ventilation system. It should provide a standard rate of air exchange while minimizing energy losses. The smaller the volume of the incoming outdoor air, the more heat can be stored, other things being equal, heat exchange with the environment, and heat generation. At the same time, living with insufficient air exchange can be not only uncomfortable but also impossible. Designers solve this dilemma by optimizing airflow volumes (air must flow exactly as needed and exactly where it is needed), recuperation, and air preconditioning (passive heating or cooling).

 

[Abrahamus]

Hi, this is an old topic, however, I would like to reopen the discussion about ventilation and which type would be much better in my brazier. My room is 10x3x2.5 and I need a good ventilation system. Since I work mainly at high temperatures, I need the air to be refreshed as often as possible. I was thinking about installing an active ventilation system in order to forcibly increase the exchange of air in the room and thus reduce the overall temperature in the brazier. I turned to specialists for help at https://niftyductcleaning.com.au/ for a consultation. They were able to suggest the best solution in order to get optimal working conditions. If any of you have done something like this, I would like to see pictures of such premises. I will be glad to any answer.