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  1. #1
    Join Date
    Nov 2008
    Posts
    30

    Cold air convection issue

    I've been scouring posts dating back to 2005 and have not found an answer to my current issue.

    I have a brand new home that has a Heat n Glo SL-550 direct venting fireplace. It is installed in an insulated bump out which has been properly insulated in all 6 spots(even spray insulation underneath the sheeting from the basement). This unit is configured to use the Intellifire system so it does not have a steady pilot on.

    My issue is that when the fireplace is not in use, it is convecting cold through the combustion air pipe which cools off the the bottom of the fireplace and creates a cold spot in my living room. While my hairy fluffy dog loves it, us humans don't so much. I've had the service tech from the company who installed the fireplace come out and was told nothing is wrong and it's the nature of the design. I've taped up all knockouts for the gas line and electrical and any other open spots with foil tape to minimize any cold air infiltration.

    My folks live down the road and have a Vermont Castings DV. Their fireplace is installed in a corner configuration and has a bit more piping(elbows, length, etc) and a different termination cap and there is no cold convection issue at all. Their knockouts are actually wide open.

    So long story short, is there anything I can do to stop the cold besides installing a always on pilot to counter the cold effect?

  2. #2
    Join Date
    Aug 2011
    Location
    Ontario
    Posts
    381
    Air from a direct vent intake cannot enter the room as it is a sealed firebox. Cold air entering bottom at knockouts is from leakage in the chase or where pipes exit the structure.
    There is no bad beer, some just taste better than others.

  3. #3
    Join Date
    Nov 2008
    Posts
    30
    Quote Originally Posted by talktowags View Post
    Air from a direct vent intake cannot enter the room as it is a sealed firebox. Cold air entering bottom at knockouts is from leakage in the chase or where pipes exit the structure.
    It seems the cold air is not leaking from the sealed firebox rather convecting cold out of the bottom through the metal. Should I have the insulation double checked?

  4. #4
    Join Date
    Aug 2011
    Location
    Ontario
    Posts
    381
    How cold is it there.? Your firebox can get cold when not in use, but to the point of feeling it in the room. ?? Do you have the option of standing pilot.? This would keep firebox warmer. I have never seen what you are describing. My guess would be leakage somewhere outside of the firebox.
    There is no bad beer, some just taste better than others.

  5. #5
    Join Date
    Nov 2008
    Posts
    30
    It's 20C in the room and 11C at the fp. I would have to add the standing pilot option.

  6. #6
    Join Date
    Nov 2008
    Posts
    30
    Actually it's more like 9C now. Only -7C outside.

  7. #7
    Join Date
    Aug 2011
    Location
    Ontario
    Posts
    381
    If everything is sealed up like you say then I would go with standing pilot option. This will help but not totally cure it. A standing pilot will help limit condensation on inside of glass as well.
    G
    There is no bad beer, some just taste better than others.

  8. #8
    Join Date
    Feb 2003
    Posts
    27

    Calling cantilever chase a Bump out ?

    If so its is the key variable. You can insulate a cantilever to high heaven, and it will always be cold especially when the surface above is cold also. You have three sides of the chase exposed to the exterior with no conditioning of the chase this heat loss will conduct into the room. The other set up you are comparing to is inside the envelope that is why they do not experience the cold issue.

  9. #9
    Join Date
    Nov 2008
    Posts
    30
    gordy - so assuming everything is installed correctly and there is adequate insulation, what estimated temperature would be considered "normal" at the bottom of the fireplace(inside taking a reading off of the far back metal) if let's say the outdoor temp is -20C(-4F) and inside temp is +20C(68F)? With these temperatures my reading was 0C(32F) using a infrared thermometer gun inside the bottom.

  10. #10
    Join Date
    Nov 2008
    Posts
    30
    Any takers?

  11. #11
    Join Date
    Feb 2003
    Posts
    27

    Correct

    If the cantilever is not conditioned from inside the room then yes it is possible to have those temps. Remember the wall above the chase interior one is insulated from allowing heat to transfer into the chase/fireplace. So the only heat that gets in the box is what ever can transfer through the doors.

    Gordy

  12. #12
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,226

    Cool weatherization and cold climate function

    You need to be thinking about 'weatherization' and not just insulation, which is only part of weatherizing. You can insulate all you want but if you don't air seal, you will freeze. Insulation does not airflow but heat transfer. Ideally, a chase will have gaskets where the chase meets the house, foam and caulk at all seams, insulation R-value per your code then sheath over the insulation. This sheathing provides an air barrier and it restrains the insulation from falling on the hot fireplace causing a fire. The inside of the chase should be completely air sealed. I prefer thin structural panels such as Thermo-Ply or Thermo-Sheath, which make a great air barrier, hold foil tape well, install quick and easy and aren't good food for mold, unlike drywall. BTW, insulation loses much of its R-value unless sheathed on all 6 sides. Even small holes can lead to significant air infiltration.

    Try to get a snake camera into the chase to verify the integrity of it. If it doesn't look sealed, you need to open it up and do it right. Mine look like a Jeffy Pop when done. Once the chase is sealed, including the cantilever and gas/ electrical penetrations, the unit installed with the venting caulked as allowed by the listed instructions then the only other source of cold air for a direct vent that has its glass properly attached and no defects in the firebox would be reverse convection at cold standby. Warm room air enters the top louver where the ice cold firebox air cools it. This air slides down behind the unit then out the bottom. This can be demonstrated with a chemical smoke puffer.

    Since you have an IPI, get a WSK 200 or one of HG's remotes that has the Cold CLimate function and make this unit into a standing pilot using its present ignition system. This is exactly what the cold climate function was made for.
    HTH

  13. #13
    Join Date
    Feb 2003
    Posts
    27

    Hearthman is totally correct

    Quote Originally Posted by hearthman View Post
    You need to be thinking about 'weatherization' and not just insulation, which is only part of weatherizing. You can insulate all you want but if you don't air seal, you will freeze. Insulation does not airflow but heat transfer. Ideally, a chase will have gaskets where the chase meets the house, foam and caulk at all seams, insulation R-value per your code then sheath over the insulation. This sheathing provides an air barrier and it restrains the insulation from falling on the hot fireplace causing a fire. The inside of the chase should be completely air sealed. I prefer thin structural panels such as Thermo-Ply or Thermo-Sheath, which make a great air barrier, hold foil tape well, install quick and easy and aren't good food for mold, unlike drywall. BTW, insulation loses much of its R-value unless sheathed on all 6 sides. Even small holes can lead to significant air infiltration.

    Try to get a snake camera into the chase to verify the integrity of it. If it doesn't look sealed, you need to open it up and do it right. Mine look like a Jeffy Pop when done. Once the chase is sealed, including the cantilever and gas/ electrical penetrations, the unit installed with the venting caulked as allowed by the listed instructions then the only other source of cold air for a direct vent that has its glass properly attached and no defects in the firebox would be reverse convection at cold standby. Warm room air enters the top louver where the ice cold firebox air cools it. This air slides down behind the unit then out the bottom. This can be demonstrated with a chemical smoke puffer.

    Since you have an IPI, get a WSK 200 or one of HG's remotes that has the Cold CLimate function and make this unit into a standing pilot using its present ignition system. This is exactly what the cold climate function was made for.
    HTH

    It should be asked what side of the house is the chase on. Is its North, west, or northwest prevailing windage will find its way into the smallest gaps in the chase. Fiberglass insulation is pretty much like an air filter once convection starts in a stud bay with fiberglass insulation the r value goes south.

    Another thought is that if house is well sealed, and the chase is not. Cold air could be pulled into the room when exhaust fans are going for baths, kitchen.



    Even after doing everything Hearthman suggests there will still be a difference in temps inside the fire box verses interior. The fact of the matter is that the chase has three sides (4 including bottom, and 5 with the top 6 if the chase extends above the roof line) exposed to the exterior, and an interior side seperating the chase. The only possible warmth to the chase is the heatloss from the wall seperating the chase from the homes interior..



    Fireplaces be they masonary, or what ever other type the worst placement is exterior walls that project from the envelope.


    Gordy

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