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Make Up Air with Direct Vent Fireplaces

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sirrox

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Discussion starter · #1 ·
I have installed two direct vent propane fireplaces. Both Regency models P40 and P36. I have a boiler going in the garage to avoid that combustion appliance in the house. However my HVAC technical advisor says I will need a make up air system to keep the house less than -5 Pa when exhaust fans are used as the fireplaces have no 'rating' or tests done to prove they can withstand any negative pressure so they are assumed to be the same as a classic wood burning open fireplace with a chimney (the ones you stoke and poke....).

I have searched high and low for something in the ANSI or CSA regarding tests but he claims they only test for internal pressures caused by the gases themselves not external pressures caused by negative pressure in the building envelope.

Can anyone shed any light on this or put a nail in the coffin which will force me to install a make up air system?
 
#2 ·
If your direct vent fireplaces are installed right, they bring in combustion for each fireplace and are sealed from the home. If you have any gas appl. you need to bring in combustion air if the appl. is not sealed combustion.
Energystar says a house that goes -3 pa or more when dryer, exhuast fan, ect... are running have a very good chance of back drafting gas appl. , that are not sealed combustion properly installed.
A company that does blower door test on homes should be able to tell you if you have proper infiltration to run fans ect.. and tell you if the sealed combustion unit are leaking.
 
#3 ·
I don't know specifics about the units your talking about but do know about building pressure testing. It sounds like your advisor does too. I am curious, has the building had a worst case comustion zone test done? Blower door test? That would tell you if make up air was required but keep this in mind. If my poke it and stoke it woodburner backdrafts I'll know it in a hurry. If your propane unit does you'll just sleep really well.
 
Discussion starter · #4 ·
thanks for the prompt replies...

stvc: good point on the sleepng well. I WILL install a makeup air for the health and safety of my family.

Blower door happens tomorrow am. As we are in the rough-in stages, the kitchen hood, dryer and central vac are not installed. Four bathroom fans are installed but not charged yet by electrical.

So we do not know what my worst case scenairo will be at this time. But the fireplaces are "sealed combustion". Now my units are made by Regency, but similar units such as http://www.kozyheat.com/944_unit.htm are rated for -50 Pa of negative pressure. The Regency technical director does not seem to understand why I need anything in writing cause they are "sealed combustion", explaining to him a water resistant watch will eventually leak beyond its rated depth still confused him so I turned to you guys for help.

The technlogy behind "sealed combustion" must be more advanced than each manufacturers word or interpretation I would think. I am hoping for a National Building Code or CSA spec (maybe something in CSA 2.33) regarding sealed combustion leakage or negative pressure.
 
Discussion starter · #5 ·
Suprising what google will bring to us.... I found this in the 2000 Minnesota Energy Code with regards to Sealed combustion:

http://www.state.mn.us/portal/mn/jsp/content.do?id=-536881350&subchannel=-536881494&sc2=-536882175&sc3=null&contentid=536894726&contenttype=EDITORIAL&programid=536894293&agency=Commerce

It would seem at the time (2000) there was no 'standard' in place. From what I can tell there still is not. Makes me wish I went with Majestic or Lennox over Regency to save $2000 bones with a simple letter of verification from the manufacturer.
 
#6 ·
Ansi Z21.88

The standard your Fp is listed to provides you enough info. The ANSI Std., section 2.32 Joints in Direct Vent Systems, tests to 25 Pascals positive pressure in the combustion chamber with the vent collar plugged. They decided to use positive pressure over negative because the test had to be done with the unit cold and yet replicate as closely as possible burning conditions. The unit must have passed at least one delayed ignition test before this test to insure it wouldn't flunk this leakage test after a severe delayed ignition. This delayed ignition test will scare the hell out of you! :eek:
With the unit plugged up and pressure taps in the combustion chamber and vent, it is pressurized to 0.1 wci (24.9 Pa) The allowable leakage rate for the combustion chamber is 4% of the input BTU rating in thousands times 15 cubic feet of flue products based on 10 cu ft. of wet products and 5 cu ft. of excess air per 1000 btus. The vent can leak up to 8% under these same conditions.

Since the unit expands as it gets heated, this test more accurately reflects true operating conditions than sticking it into a box and sucking it down. However, most mfrs. have conducted their own pressure house studies to know the depressurization limits of each unit and where the critical points are through IR thermography, tracer gas, and smoke puffers. This info. is proprietary and closely guarded. Beware of claims someone has "tested to a certain std.". Did it pass? Says who--the mfr. or a recognized testing lab? Biiiig difference.

Hope this helps.:D
 
#7 ·
sirrox said:
thanks for the prompt replies...

stvc: good point on the sleepng well. I WILL install a makeup air for the health and safety of my family.

Blower door happens tomorrow am. As we are in the rough-in stages, the kitchen hood, dryer and central vac are not installed. Four bathroom fans are installed but not charged yet by electrical.

So we do not know what my worst case scenairo will be at this time. But the fireplaces are "sealed combustion". Now my units are made by Regency, but similar units such as http://www.kozyheat.com/944_unit.htm are rated for -50 Pa of negative pressure. The Regency technical director does not seem to understand why I need anything in writing cause they are "sealed combustion", explaining to him a water resistant watch will eventually leak beyond its rated depth still confused him so I turned to you guys for help.

The technlogy behind "sealed combustion" must be more advanced than each manufacturers word or interpretation I would think. I am hoping for a National Building Code or CSA spec (maybe something in CSA 2.33) regarding sealed combustion leakage or negative pressure.
Click to expand...
Sounds like you are on the right track to an energy efficient and healthy building. I suspect the blower door test tomorrow is to test the envelope of the building when it will be easy to correct any bypasses detected. By the way, it will be depressurized to -50PA for that test. A final blower door test should be done after everything is done, you'd be surprised how much fan dampers etc. can leak. Also, some of those kick ass kitchen hoods move alot of air and can seriously depressurize a tight house. Are you building a energy star home? Not many people take these steps otherwise.
 
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stvc
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