Do Magnetic Heating Vent Covers Work?

Discussion in 'Off Topic' started by Dirigible, Dec 11, 2007.

  1. Dirigible

    Dirigible Diamond Member

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    The questions:

    - Has anyone used magnetic heating vent covers to stop heating a room or area of a house?
    - Do they work?
    - If so, do you have any recommendations on specific brands or things to look for or are they all pretty much the same?
    - Any other alternatives that would work better?

    The reason for the questions, if you're curious (yes the below is obvious, but this lets me waste more work time):

    So now winter is upon me and it's incredibly freezing cold outside. Today's high is supposed to be 54 F! Holy cow, that's colder than a witch's teat! Subarctic, even! Awright, I admit I'm a wimpy native Californian who'd die if exposed to temperatures that are even remotely chilly. To prevent said death I've turned on my furnace.

    The attic in my house is finished and heated, but I almost never go up there and would prefer not to spend money heating it up. I closed the vents up there, but there's still a significant amount of heated air whistling through.

    So I'd like something that would more effectively seal off the attic vents, but are not permanent. I formerly had my home office up there, and may make use of the space again.

    Thanks for your help!

    Edit for more detail: My vents are on the wall, so any vent cover would be fighting gravity.
     
  2. Maximus96

    Maximus96 Diamond Member

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    i bought a pack from home depot the other week...they're cheap pieces of soft and rubberized magnet. trimmed to fit two of my closed vents but both fell down when i turned on the heat. end up wasted $3.50...
     
  3. Dirigible

    Dirigible Diamond Member

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    Thanks for the info. That's the sort of thing I fear happening and why I posted before purchasing.

    Anyone know of any magnetic or other types that actually work?
     
  4. bonkers325

    bonkers325 Lifer

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    cover it with a large garbage bag and put a heavy box over the vent
     
  5. sdifox

    sdifox No Lifer

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    actually, you are not supposed to cover any heat, it's whole house heating, if a section is not as well vented, the heat will move toward that spot, which defeats your intention.
     
  6. spidey07

    spidey07 No Lifer

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    say whhaa?

    Cover the vents on places not used/in need of heat to improve the rest of the place, makes a huge difference and is more energy efficient as well.

    As as the magenetic things mine fell off as well.
     
  7. dandruff

    dandruff Golden Member

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    huh? are u saying you have thermostats measuring temperatures everywhere in ur house? most standard houses below 3k sqft have one or two zones.

    we have closed vents in our master closets / guest room ... u can even use duct tape or get better magents or vents that close tightly. hth!

     
  8. Dirigible

    Dirigible Diamond Member

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    I don't think this is true. If a section of the house is pretty well sealed off, as my attic is, it'll stay colder and save me moolah. It's not like it's a portion of an open floor plan that I'm cutting heat to.

    Curses.


    It's ghetto, but I dunno if it's fabulous.

    Since my vents are on the wall, this'd be trickier than if they were on the floor. If no one has any other ideas I may give this a shot, maybe using some foam that'd conform to the vent/wall/box contour and give a better seal.
     
  9. sdifox

    sdifox No Lifer

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    http://www.consumerenergycenter.org/myths/vents.html

    Usually, you have a main trunk that goes vertical (usually centre wall of the house) and then it splits off. unless your attic is hermetically sealed off from the rest of the house, it is part of the system. Bottom line, sealing a port just forces the heated air to find a way out, which usually means the joints of the duct system. No, they are not air tight. Don't ask me why they don't silicon the joints and fasterner holes.

    But if you really want to close the vent, just tape some plastic sheet over it. Since you are not up there, aesthetics is not an issue.
     
  10. Dirigible

    Dirigible Diamond Member

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    Wow, that article's counterintuitive. If my reading is correct, the losses are mostly due to duct leakage.

    Not sure if it's true for my house, because (a) it was built in 1910 and has no insulation that I'm aware of (from the article: "this may have worked with older, non-insulated homes"), (b) it is the ducts furthest from the furnace, (c) the ducts heading up there are in conditioned space, not outside conditioned space, (d) it is a small percentage of the registers that are closed, and (e) the system was supposed to be two zone with the attic having internal automatic air valves that close off the attic but it broke and I'm too cheap to call the repair man. So it seems like some of the assumptions of the article are wrong, and just about every factor indicates that if anyone has a shot at saving cash, I would.

    Hmmm... Do I have old utility bills so I could do a comparison? Might be an interesting experiment.

    I don't like the duct tape idea, because it leaves residue when removed and the space may be used in the future.

    Edit: But on the plus side, that article gives me a reason to be lazy and just do nothing. Sweet! You rock, sdifox!
     
  11. dandruff

    dandruff Golden Member

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  12. Dirigible

    Dirigible Diamond Member

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    Ducts heading to the attic are inside conditioned space. Ducts leading elsewhere in the house are in unconditioned space (the crawlspace under the house). I'd need to crawl around down there to see how things are connected and if closing off the attic vents would increase the pressure in the other ducts.

    Edit: to fix quotes.

    Right now I'm thinking that closing the vents closed off most of the air flow, but allows some pressure release. So that may be a good compromise and I'll not completely seal the vents right now. Hopefully I'll remember to check my utility bill and compare my natural gas usage.
     
  13. Amused

    Amused Elite Member

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    This is very easy.

    Stop thinking of the vent and think of the duct.

    Unscrew the vent cover and stuff the opening with newspaper. Use enough to wedge it in tight and block all airflow. Also, use large peices and ball it up tight so you don't lose any in the duct.

    No tape, no mess, no unsightly plastic and quickly reversable when you need cold air up there in the summer.
     
  14. Dirigible

    Dirigible Diamond Member

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    That would work well. If I decide to block it completely I'll do something like that. Open vent, seal the inside so pressure would keep sealant in place.

    Not really relevant, but I have no need for cold air. I have no AC. Even without it my house only gets up to 80 degrees at most, and days that hot are rare. I live directly east of the Golden Gate and get plenty of fog in the summertime.
     
  15. Jeff7

    Jeff7 Lifer

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    All my vents are on the floor, so the magnetic things work ok. Only issue - the air will still try to find a way out of the vent, so if the joint between the vent and the duct is loose, air will whistle out of there. Solution: double-sided tape plus some insulating felt, wrapped around the perimeter of where the vent fits inside the duct. That kept the air from hissing through there, and the magnetic thing seals it up completely.

    For wall vents - maybe get some neodymium hard drive magnets? :D

    I close off the vent in my apartment's bedroom during the day, which keeps the warm air downstairs in the livingroom.

    What about duct-taping the seams or joints on the ducts themselves? Are they easily visible? Maybe you could try foil tape instead, it might not leave as much residue, if you want to keep the ductwork tidy.
     
  16. jagec

    jagec Lifer

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    The heat has a plan, just like the Cylons!



    Use a garbage bag and some duct tape to seal off the vents. If you want it to look prettier, use a piece of thick glossy paper instead.
     
  17. Uppsala9496

    Uppsala9496 Diamond Member

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  18. Thegonagle

    Thegonagle Diamond Member

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    Don't forget to cover the return air vent, too, otherwise warm air will get sucked into the room under the door, somewhat defeating the purpose.

    Also, don't try to cover too many vents, otherwise you could block so much airflow that your furnace overheats. (I've heard not to close off more than 10-20% of your vents as a rule of thumb.)

    Sorry I don't have brand advice for the magnets, but if the $4 covers from Home Depot don't work for you (possible, since that type of magnetic material tends to be fairly weak), I'd just use a plastic bag and some masking tape.
     
  19. sdifox

    sdifox No Lifer

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    nope, just plain old thermodynamics. I meant the air will slowly average itself out in terms of temperature, that is how forced air heating works.
     
  20. jagec

    jagec Lifer

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    Funny you should mention thermodynamics, seeing as how I've taken LOTS of those classes.

    The closed vents, closed door to the attic, and solid walls/ceiling present a very decent thermal barrier, slowing heat transfer significantly. This is more than enough to allow an unheated part of the house to be quite a bit cooler than a heated part, although it won't cool all the way down to ambient temperature in most cases. This will save you money.

    Now, if he blocked off the vents and then left the door open, the "unheated" room wouldn't be nearly as cold, and that would defeat the purpose of blocking the vents in the first place.
     
  21. sdifox

    sdifox No Lifer

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    Except houses are not air tight on the exterior envelope and we can forget about room to room. Stupid ducts themselves lose a lot of heat, be it radiant or leakage. If you had airtight low loss ducts, windows and doors (interior) , and are about to shut off branches at the branch as opposed to the end point and not create too much back pressure for your blower, then yeah, you can save some money. Except every single item I listed in the average house is leaky as hell.
     
  22. jagec

    jagec Lifer

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    Orders of magnitude. Air sucks for heat transfer, and so you need a fair bit of flow to make a difference. A bit of leakage isn't gong to do much.

    Even without SEALING the vents, simply closing the vents in one room and locking the door will result in a VERY perceptible difference in temperature compared to the other rooms in the house. This is an easy experiment to prove. Sealing the vents just makes it ever so slightly colder.