Forced air gas car kiln firing questions?

[Biglou13]

I’m at a community studio. They are having issues firing a smallish car kiln. Kiln is indoors .   I’m unsure how kiln is vented / how exhaust is routed.  They are saying they are having issues with hvac system causing  back pressure on kiln causing flame to come out .  firing    Is going on a month late.  My guess is  that something along exhaust is partially blocked. It is winter here and it is frequently windy outside. What could be causing this back pressure?  
 

I have good amount of experience with. Cone 6, wood fired kilns. they are quite secretive about firing I wish they would let us observe, would be great learning experience. 

[Bill Kielb]

Gas fired appliances need ventilation, the simplest form would be a properly sized natural draft hood. Natural draft hoods are one of the simplest designs because they are simply a hood above the appliance with some space available for dilution air (room air) to also rise up the flue pipe. This open space on older natural draft appliances (boilers, water heaters …) was often called the draft diverter. Quite often before the flue could warm sufficiently this space would allow the cold downward draft to be diverted so as not to blow the pilot out in the off cycle. What COULD it be? Common would be a properly designed flue for the kiln not allowing the cold backdraft at startup.

You mentioned HVAC issues, well gas appliances need their own source or combustion air as well sized for the appliance and positionally sized in one of several very specific ways to combat stack effect, dilution air requirements etc…

Further: exhaust HVAC appliances need makeup air. Proper design and accounting is important so as not to defeat any natural draft appliances. Does the studio have a paint spray booth or other exhaust appliance affecting this?

What could this be? It’s simple stuff but takes real design experience and the potential to be a real health safety issue with carbon monoxide or just a nuisance issue like pilots blown out exists. My experience often these are designed by folks not skilled enough to do so or a failure to follow the manufactures design requirements. Hidden issues like other exhaust appliances with makeup air issues are common as well.

If folks are silent or secretive about it, maybe they are not skilled enough to understand all the potential design issues. It’s fairly straightforward but truly requires combustion air zone training in addition to flue design skills. I can’t tell you how many times I have seen direct vents installed for natural draft. My best thought here is find an HVAC contractor with these skills and the ability to understand and follow code requirements. The solution is generally easy, just not necessarily intuitive and unfortunately found more in older techs than younger as these appliances disappear from use in favor of sealed combustion higher efficiency stuff.

zI could be several things unfortunately, I included a simplified drawing of some of the interactions of these required airflows you may find of interest in this thread https://community.ceramicartsdaily.org/topic/39240-skutt-envirovent-still-allows-fumes/?do=findComment&comment=251190

 

Edited January 5 by Bill Kielb