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  1. #1
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    Default Are covers required for filters?

    This may not be a big deal, but would like confirmation.
    Furnaces in most newer homes seem to usually have a cover over the filter opening, so I assume that it is required. It makes common sense, both to protect household air from gas fumes etc, and also from an efficiency point of view, but am not sure if I can see the applicable code in IRC.

    2006-IRC M1602.2.5 - "Prohibited sources" regarding return air states that a return air supply cannot be in same room or space containing a fuel-burning appliance. But this really is not a "return air" vent, just a gap in the ducting around the filter housing. (see pic).
    Or, is this covered by M1601.3.1 regarding "Joints and seams"??

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  2. #2
    Join Date
    Mar 2007
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    Default Re: Are covers required for filters?

    Terry,

    You are kidding right? A gap would be a small opening. What you have there would indeed put the return air immediately adjacent to the furnace. There is no way that air is going to travel down a duct when it can take the path of least resistance. If this is in a closet, the blower will depressurize the closet and pull the combustion exhaust back down the flue pipe and distribute it throughout the house. If it is in the garage (like many around here are), it will pull vehicle exhaust into the household air.

    Makes me wonder what nimrod put this together.

    Department of Redundancy Department
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  3. #3
    David Banks's Avatar
    David Banks Guest

    Default Re: Are covers required for filters?

    Quote Originally Posted by Terry Beck View Post
    This may not be a big deal, but would like confirmation.
    Furnaces in most newer homes seem to usually have a cover over the filter opening, so I assume that it is required. It makes common sense, both to protect household air from gas fumes etc, and also from an efficiency point of view, but am not sure if I can see the applicable code in IRC.

    2006-IRC M1602.2.5 - "Prohibited sources" regarding return air states that a return air supply cannot be in same room or space containing a fuel-burning appliance. But this really is not a "return air" vent, just a gap in the ducting around the filter housing. (see pic).
    Or, is this covered by M1601.3.1 regarding "Joints and seams"??
    You are correct. Filter should fit properly and have cover. Should be sealed system.


  4. #4
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    Mar 2007
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    Western Montana
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    Default Re: Are covers required for filters?

    Gunnar,
    Furnace is in a vented crawlspace, with a fresh air supply for combustion/dilution. (contruction 2003)
    There are lots of nimrods around here, nimords that install furnces, nimrods that install fireplaces, nimrods that do electrical, nimrods that install water-softeners, nimrod general contractors are our speciality. Most the really interesting nimrods do their best work outside of city limits where the nimrods are only see an occasional state electrical inspection. What you see in the picture is pretty much normal around here, except for newer homes built inside city limits in the last 2-3 years (there's a lot more homes outside than inside cities in Montana). Probably some nimrod home inspectors as well.

    So, I take it that the anwer to my question is covered by M1601.3.1 regarding "Joints and seams"


  5. #5
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    Exclamation Re: Are covers required for filters?

    Yes, you can address it in M1601.3.1 You can also pick it up in ANSI Z21.47 Gas Fired Central Furnaces, which requires an interlock to prevent furnace operation if the blower (filter) access panel is not in place. This is why there is a microswitch on the lower panel which covers the blower. If the filter is located in the return next to the blower, you could make the case it, too should be interlocked. Otherwise, why do one and not the other?
    FYI, I have NEVER seen an interlock on a filter cover. I find most wide open. You can also explain the dirt that bypasses the filter will clog the A coil.
    HTH,
    Bob

    Keep the fire in the fireplace.

  6. #6
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    Default Re: Are covers required for filters?

    Bob is right again (not that anyone is surprised). I had forgotten the blower door/cover switch.

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  7. #7
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    Exclamation open filter slots

    Thx Gunnar.

    Just to elaborate on this important topic, let's explore the consequences of an uncovered filter slot located in the return right next to the blower-
    1- You can depressurized the Combustion Appliance Zone to the point it induces flue gas spillage or even backdrafting. I find it kills fireplaces all the time. Can pull exhaust out of a water heater's draft hood right into the return and then you have a nice carbon monoxide distribution system. That's why the codes require ducts sealed for at least 10 ft. from the appliances.
    2- Dirt can blow right past that filter, due to the sloppy fit, where it clogs the A coil on the supply. The result there is short term drop in airflow, whether heating or cooling, reduced cooling capacity, straining the blower, higher temps. in the heat exchanger (HX), which can lead to premature failure resulting in CO spillage, and whack out the delta T (temp. difference of convection air in and out, which whacks out the combustion numbers, which can cause drop in efficiency or increased CO production. Whew!
    3- If you have an opening at the return plenum, then as the path of least resistance, you will suck in CAZ air instead of air from the distant rooms. Aside from the CO issue in #2, you get air stagnation in the other rooms. Meanwhile, whatever is in the air in the CAZ such as moisture, mold, odors, radon, stored chemicals such as paint, etc. all gets circulated around the house. Bad for indoor air quality (IAQ)
    4- You system was (ideally) designed, installed, tested and balanced. If you open a breech in the return, it throws off the static pressure in the return so you get a false External Static Pressure (ESP) reading. The tech reads the max. ESP on the rating plate then makes a judgement based on improper data as far as adjustments go. He may think the duct system is well designed when in fact it is asthmatic. Since it cannot breathe from the far reaches, it chooses the path of least resistance and breathes in basement air fooling the tech into thinking everything is hunky-dory.
    5- The delta T has an effect on the combustion efficiency and thermal efficiency of the unit. A trained tech, such as Davidr, can tweak a unit so it optimizes combustion efficiency and overall energy efficiency. He takes into account multiple combustion analysis, duct pressure readings, calculate CFM, measure pressure drop over the filter, humidifier, and A coil, adjust the blower fan speed-all to maximize performance, increase durability and longevity and minimize the chance of CO spillage and problems.
    6- If you are pulling air from the basement pumping it into the rooms with inadequate return air, you can pressurize some rooms. This can force air under high velocity under doors and walls leaving the telltale black stripes in the carpet as it filters dirt. It can, in extreme cases, force moisture into interstitial wall spaces where it can grow fuzzy stuff.
    7. If you aren't getting comfortable, you tend to run the furnace or A/C more, which results in wasting energy.
    8. the more hours your system runs, the more maintenance it will require. Not only will your filter clog faster due to extended run times but everything else I mentioned will wear out sooner.
    9. If the CAZ is depressurized from a lack of adequate makeup air (MUA), aside from killing you with CO spillage, it will kill the blower on your air handler as it struggles to keep up.

    I hope Davidr reads this can corrects me and adds his own flavor to this discussion. He's the tech you want to come to your house.

    Just trying to stir some thoughts,

    PS- the filter in the OPs photo, is, of course, too big. They can comply with the sealing requirement by using foil tape over a steel sliding cover. Another trick I've used to make a removable cover is magnetic sign material cut with scissors to overlap. Doesn't have the interlock but, hey, it seals and is removable.
    PSS- that filter is installed backwards!
    Bob

    Last edited by Bob Harper; 07-07-2008 at 12:08 PM. Reason: another burst of brilliance
    Keep the fire in the fireplace.

  8. #8
    Join Date
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    Default Re: Are covers required for filters?

    Bob you need to write a book if you haven't already that was awesome!

    If you want to see if the blower in any air moving device in a building is going to affect draft all you need is a 20$ dwyer 460.

    By placing this in the flue and watching the appliances draft while it is firing start kicking on the fans.
    If the ball in the 460 drops you have flue interference from that air moving device.
    If the ball goes up that room is being pressurized by that air moving device.
    Unless there is a fresh air duct tied into the return that means the rest of the air is coming from another source which is probably not good.
    Keep in mind a fan is a constant volume machine, for every 1 CFM in you will have 1 CFM out.

    BTW just because you have draft in a flue doesn't mean that appliance is venting.

    Measured Performance more than just a buzzword

  9. #9
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    Talking Re: Are covers required for filters?

    Hah!, if I do write one David, I'll certainly include you in the credits!

    "BTW just because you have draft in a flue doesn't mean that appliance is venting. "

    This is a great discussion point for this group. We've discussed many methods inspectors use to ascertain if an appliance is venting properly or not. I've argued against using smoke/ mirrors/ open flames etc. near a draft hood because the most they can tell you is if room air is getting entrained up the stack or if some humid air is spilling out (mirror). None of these prove flue gases are making it out of the house. So, to follow on Davidr's point, explain how too much draft can cause carbon monoxide to enter the home. I think ya'll will enjoy this!
    Bob
    __________________

    Keep the fire in the fireplace.

  10. #10
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    May 2007
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    Frankfort, KY
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    Default Re: Are covers required for filters?

    Just to add a little more to Bob's comments there is a suggested checkout procedure for draft hood equipped appliances that is included with most of the GAMA venting tables I ever received. It is the procedure to test for spillage at a draft hood.

    If I am not mistaken the procedure is based off of text in the National Fuel Gas Code.
    With the amount of knowledge here regarding codes I'm sure someone can point to the exact section.

    If this procedure is followed exactly as written and the situations in the field are right the person performing the test might not walk out of the room the appliances are located in.

    Just something to think about.

    Measured Performance more than just a buzzword

  11. #11
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    Default Re: Are covers required for filters?

    Bob & David,

    Whew! While all of that is valid, a lot of it is beyond what most of us are looking for.

    Department of Redundancy Department
    http://www.FullCircleInspect.com/

  12. #12
    Join Date
    Aug 2008
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    Pleasant Hill, Iowa
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    133

    Default Re: Are covers required for filters?

    Alot of information for just a filter cover, put the dang cover on!
    Good information though !


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