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Thread: Heat Detector in attic

  1. #1
    Sr. Systems Engineer, Biotech
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    Default Heat Detector in attic

    Iím putting in a 135 deg F heat detector in an attic. The house is in New England and the temps vary greatly. The attic is used for storage and the gable ends are vented. I need some detection device up there. There are no ridge or soffit vents and there is also no ventilation fan. This is as the house was built in 1962. I know it gets hot up there normally, but how hot Iíve never measured. Might I worry about nuisance trips with using a 135 deg heat detector? I'm considering trading this one for a 200 deg one.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    WITH soffit and ridge vents, my townhouse (used to) get over 135-degrees in the attic. I put in a radiant barrier, and that dropped it a fair amount. I think you'd find 135 is too low. I'd be very careful about what I put up there for storage...some things just don't like the temperature and humidity extremes common for up there. You really should consider some ventilation, and a radiant barrier would help as well. A typical asphalt roof can get way too hot to touch in the summer, and that will heat up the roof decking a LOT on a clear, sunny day.
    Jim DeBruycker
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    In the trades Dana's Avatar
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    What is the intended purpose of the heat-detector?

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    The environmental conditions of the attic are too extreme to put a std. smoke detector so I'm adding the heat detector. I've updated the whole house with interconnected detectors and want the protection / detection up there as well.

    After a little research, my thoughts are being confirmed, 135 is not high enough and I'm going with the 200 deg heat detector. A ridge vent isn't a big deal (the carbide blade is in the skill saw box). Just need to find a close match to the shingles. That's an afternoon project for later on this spring. The soffits are all capped in vinyl so putting vents in there are a little more work than I think I want to get into (this isn't my house). Convincing the home owner after 48 years of living there that they now need an attic fan won't go over well

    Thanks

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    In the trades Dana's Avatar
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    Quote Originally Posted by helix3 View Post
    The environmental conditions of the attic are too extreme to put a std. smoke detector so I'm adding the heat detector. I've updated the whole house with interconnected detectors and want the protection / detection up there as well.

    After a little research, my thoughts are being confirmed, 135 is not high enough and I'm going with the 200 deg heat detector. A ridge vent isn't a big deal (the carbide blade is in the skill saw box). Just need to find a close match to the shingles. That's an afternoon project for later on this spring. The soffits are all capped in vinyl so putting vents in there are a little more work than I think I want to get into (this isn't my house). Convincing the home owner after 48 years of living there that they now need an attic fan won't go over well

    Thanks
    A ridge vent might be a bigger deal than you think- easy to install, but probably not be the right thing- it won't reduce attic temps by more than a couple of degrees, but will likely increase the mold hazard here.

    A better (but more expensive) solution is to spray the interior of the roof deck & gables with 4-6" half-pound foam, ensuring that it's air tight at the soffits & ridges rather than adding attic ventilation. That will lower the summertime attic temp considerably, without increasing the stack-effect infiltration drives on the building. Typical 1962 construction had maybe 4-6" of batts or loose fill insulation which may have been upgraded to something better in the interrim, but unless it was air-sealed at religiously at the attic floor when upgraded, opening up attic ventilation will create a real wintertime heat leak, pulling moist conditioned space air into the attic to condense. Opening up attic ventilation to the point where even that dries becomes a HUGE heat leak. Attic ventilation is something of a solution-problem: It solves some of the humidity problems related to stack effect, but can also drive those same problems unless done massively (usually at a cost in energy-efficiency.)

    If the house experiences ice-damming in winter, roof-deck insulation will reduce that considerably as well. In most of the NE states there are subsidies for adding attic/roof insulation. Half-pound (open-cell, "Icynene","Sealection 500" et al) foam is preferable to closed cell on the interior, since it won't trap moisture in the roof deck creating rot conditions, and roof leaks are more easily detected & located (find the staining &/or drip.)

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    I live in a row of townhouse condominiums. After installing a radiant barrier on the bottom of the roof rafters, and after a snow storm, I have snow remaining on my roof as much as a week after all the others have melted...so, it does help keep heat from the attic from getting to the roof surface. In the summer, it dropped the attic temperature considerably, enough so that at the end of a long sunny summer day the ceiling temperature was no higher than an interior wall. So, it was a cheap and easy (partial) solution to a really hot attic. That radiant barrier might shorten the shingle life since they are getting heat from both sides. Foam would be better there, I think, but can't confirm. If you don't have enough vents for the fan to exhaust properly, you decrease the efficiency considerably. A big fan can cost a fair amount in energy costs as well.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    The insulation was updated a while back and there is a thick blanket of it sitting up there covering the ceilings and it is tight. I built a few raised platforms above the insulation and have some items stored up there (Christmas tree, decorations, luggage, etc..) There is no issue with the roof or moisture or mold or anything else. I have previously replaced all of the windows (new construction, not replacements) and outside door units. Every exterior wall, window and door are well insulated. The house is efficient, the oil burner less than 5 years old and oil consumption was low over the last winter. There are no issues except for that the attic will be getting hotter than 135 deg F, so I'm putting in a 200 deg heat detector and will take it from there.

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    In the trades Dana's Avatar
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    If it hasn't been having moisture issues, don't create them or reduce energy efficiency with a new ventilation scheme.

    A perforated aluminized fabric type radiant barrier mounted between on the rafters (with a space between the rb & roof deck) would lower the peak attic temps (and lower the AC load) without changing the moisture issues. The shingle-life issue is small- it would have no more than ~10% reduction in average shingle life if the roof pitch is over 2:12 (which most are in the snowy NE), and shingle COLOR would have an as-large or larger effect. But simply going with a 200F heat detector is probably the "right" thing to do- radiant barrier will never pay for itself in energy savings with a super-insulated attic- you'd only want to go there to reduce the magnitude of thermal cycling of the stored goods.

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