CAZ: gas fireplace depressurization limit

Combustion Appliance Zone Test: Does anyone know how to approach a wood or gas fireplace depressurization limit when doing a CAZ test?

For a wood fireplace using combustion air from the home interior, I set a blower door at 300CFM to simulate the fireplace.

However, if the fireplace has outside air source, there has to be some sort of depressurization limit. It doesn’t make sense that setting the BD at 300CFM is the proper procedure.

I tested a tight home with a wood fireplace with outside air source and gasket sealed door (less than totally sealed). CAZ worst case: kitchen fan, bathroom fans, and dryer on, I measured -45pa! Power vented water heaters have -15pa limit. Closed combustion have -50pa limit. What’s the limit on this fireplace? I’m sure I exceeded it, and reported it as such. But wondering what is the limit.

I can’t find this information anywhere in my searching. I’m BPI Building Analyst certified.

Their is a huge amount of information on the web looks’ like you did not try… GOOGLE

I did and found some .

gas fireplace depressurization limit - Google Search

All the best… Roy

Thanks for your comments and search. In fact I did spend time doing a search. Obviously your search came up with the information I needed. Thanks again!

Answering my own question now, from “BPI Interpretations, Clarifications, and Comments: b) If the gas fireplace is a sealed combustion insert, a spillage test is not required. It is recommended to use smoke directly in front of the unit while operating (any signs of spillage may indicate an issue). Carbon monoxide must be measured at the exterior termination point. If this point is not accessible, measuring ambient carbon monoxide directly in front of and above the unit is recommended. Draft testing may be impossible to perform since there may not be an appropriate location in which to properly place a test probe. Any corrective action required is stated in Building Analyst Standard, page 13. CAZ Depressurization Limits for a sealed combustion appliance would apply.”

Meaning the depressurization limit for a gas fireplace with sealed combustion and an outside combustion air source is the same as a sealed combustion gas furnace, namely -50pa

The comment in the BPI standard about testing the seal of any opening is an important comment. There are wood fueled fireplaces with outside combustion air source and access doors that have compromised gaskets. In that case, the seal of the door is critical once again. Not sure if these fireplaces are defined as sealed combustion units. They may be more like a power vented furnace with combustion air supplied to the furnace enclosure through a pipe from the outside, or even like a natural vented appliance. In that case, the CAZ limit is -15pa, or even as low as -5pa. I’ll have to do more research on this item, using google.

I just performed an energy code compliance test including a CAZ of -42pa and a sealed gas fireplace. A few months past, I had a -45pa CAZ reading on a home with a wood fired fireplace with gasketed doors and outside combustion air source. I found -10pa as a standard with some States for wood heat stoves and likely for sealed door fireplaces. None of these are BPI or ANSI standards.

As homes are built tight, this depressurization can become a fatal condition in terms of carbon monoxide, something to not miss during an energy audit. Thus my initial question and concern.

Late to the party here but if I were to get to -45pa on a CAZ test I would be extremely concerned.

What is the pressure in normal conditions?

I often do not get to 50 with my blower door

Agreed, and so my post. I don’t recall exactly any more, but the pressure under natural conditions was normal, around -2pa.

I live in far northern Minnesota, and I see a lot of well built, tight homes. We have an energy code here that has a -3pa limit on leakage at -50pa. I’ve followed the BPI procedures that Roy pointed me to. Yes, those buildings with CAZ results in the -35 area +/- area are concerning to my thinking, even though they are within limits for closed combustion appliances. What happens as those appliances age, or an unnoticed crack develops in the combustion or heat exchanger, or in the flue? What if a new exhaust fan is added, unknowingly reducing the depressurization beyond -50? What if an appliance with a -15pa limit is installed in the home at a later date? Observing a CO monitor properly placed in the home is another important item I make sure to check and document.

My energy code testing has expanded beyond simply doing a blower door test, as required by our energy code. I include a CAZ appliance test plus confirm that a CO monitor is properly placed. We have a CO death here every few years, so home safety is an important issue beyond code testing.

BTW, I’ve only had one time I couldn’t reach -50pa on my blower door, and that was a very large commercial dining area with numerous leaks.

when you consider that 50pa is like putting a 20mph force on the entire surface I just don’t see a bathroom fan or kitchen fan achieving that no matter how tight the home. Perhaps complete supply leakage into unconditioned space on a large air handler would be a jump.

I have a bit of experience with pressure testing.

  1. any time a house under natural conditions is at a negative pressure I am concerned your house should not suck

  2. I always take elements one at a time during caz beginning with smallest bath fans then hood fans then air handler note each change open close doors to achieve greatest pressure delta

Anomalies and I can only think that a 50pa Caz test is an anomaly I would doubt my findings and double check.

I would think on the tightest of buildings the normal fans of a home cannot achieve -50pa I would expext them to choke out and not have the power to achieve -45. CFM in = CFM out

Home Energy pros would be a good place to go with this there are poster there that have more expertise than I. I am not an engineer or a phd but a fairly competent technician own a BD since 2007 and have done my fair share of testing. You are in a different region

I do suspect something went wrong with your testing


Wondering if you’ve had buildings in San Diego that test under 1 or 1.5 ACH-50? The two buildings with a CAZ in the -45pa area were both under 1.5 ACH-50pa. A lot of older buildings around here test about 6/7 ACH-50pa, so the high CAZ is not possible.

I’m confident with my readings. I follow BPI procedures, and I’m very skeptical, back checking for errors and looking for other evidence to support an unusual reading. Your comment to the issue of an error is important. These particular buildings are rare and unusual. I’ve probably done almost 50 blower door tests, and I’m talking about maybe 5% of these tests.

Maybe I can find some more local folks doing this kind of work and see if a high CAZ on a tight building is something they find now and then.

Well with our weather 72 degrees inside and out most of the year our construction is rarely designed tight. There are a few passive hus projects here and there but thus far I have not tested on them. Boutique type buildings and not common. I have tested some tight homes. I am not always running caz test though as different tests for different programs.

Like I suggested the Home Energy Pros website or at one time there was a BPI group on linkeden run by David Butler where a question like this would get better answers. It used to be guys like David whom is a retired engineer and has immersed himself in building science and was quite knowledgeable. Allison Bales of Energy Vanguard and Colin Gauge of Retrotec would chime in on answers at times. It has been a while not sure who is in those chat rooms now but much more experience in that field i believe than you will find elsewhere on the web

Notice I say I suspect not that I know. I was not there and am not putting down your experience nor methods.

And perhaps it is possible but it would seem to me the fans activated during a caz would choke out before reaching that pressure. I think you were questioning it yourself hence the post

I am curious if it is possible. It might be and common and my doubt misfounded I question myself often when testing

Building Science is a bit different than the HI in my view and I would ask Building Science questions there rather than here

Thanks much for those links Glen! Found the Home Energy Pros site, but maybe the BPI group on LinkedIn is gone.

And about your “suspect”, I appreciate that comment. Unusual building issues are not always obvious, and one has to keep an open/questioning mind.

The group it appears is no more. I was active there in I think like 2009 -2012

There were great discussions and David Archived them. Worth browsing through not sure how to search them.

Home Performance Forum Archives

It looks like David is active on Home Energy Pros that is a good thing he has the ability to take complex ideas and simplify them. He was always good at moving discussions forward rather than dominating like some experts or no experts do.

Allison and Energy Vanguard is worth while to subscribe to.

is been a while for me I think I will get my feet wet there again

Also if not already on your bookmark visit here

Building Science Corporation | Consulting & Architecture

I was luck enough to be small class with John Tooley

Anything you can find from him is informative and interesting. One of the pioneers of testing and Home Performance and quite possibly the greatest trainer in the industry Peter is the marketing guy who has been in this space for a long time