Insulating the exhaust from a microwave and stove: advice?
November 16, 2015 3:57 PM Subscribe
I have a microwave above my rangetop stove. Its exhaust runs through the back of the cabinet above the microwave. In the winter, this cabinet can get pretty cold since that exhaust is open to the outside of the house. I'm worried about wasting energy (ala, this cabinet is letting the hot air out of my house). What can I do? Should I bother?
I planned on insulating it and got some of this rigid foam insulation. I just noticed that its "max service temperature" is 165 degrees (F). Would it catch fire if I was blasting away on my stovetop? I don't know how hot a stove/microwave chimney gets.
Here is a photo of the exhaust/chimney in the cabinet
I planned on insulating it and got some of this rigid foam insulation. I just noticed that its "max service temperature" is 165 degrees (F). Would it catch fire if I was blasting away on my stovetop? I don't know how hot a stove/microwave chimney gets.
Here is a photo of the exhaust/chimney in the cabinet
Second the flapper valve at the outside opening. If the vent doesn't have one get one for sure, and if it does, check that it swings down into place and seals properly when the vent isn't venting (and that it swings freely open when it is).
I wouldn't expect a range hood vent to get to 165F under normal use, but if you're concerned maybe fire up the range at full blast and take a thermometer to the duct.
posted by MoTLD at 5:09 PM on November 16, 2015
I wouldn't expect a range hood vent to get to 165F under normal use, but if you're concerned maybe fire up the range at full blast and take a thermometer to the duct.
posted by MoTLD at 5:09 PM on November 16, 2015
I wouldn't hesitate to do that. I looks like you have room to leave an air gap between the insulation and the ducting and still clear that outlet cover. I would glue up a "U" shaped foam insert with Gorilla Glue and pop it in there.
You are still going to have cold air coming in through the exhaust vent intake. I think I've seen foam inserts that you put into the outlet, but that leaves the whole thing inoperable.
posted by humboldt32 at 5:16 PM on November 16, 2015
You are still going to have cold air coming in through the exhaust vent intake. I think I've seen foam inserts that you put into the outlet, but that leaves the whole thing inoperable.
posted by humboldt32 at 5:16 PM on November 16, 2015
You can't block the vent pipe by code most places.
You shouldn't use a flammable material to insulate a hood duct. If the duct catches fire a flammable insulation can catch fire. Also polystyrene insulations need to be covered by a non-flammable layer in residences (in Canada anyways, your profile doesn't say where you are located) because the fumes given off when burning are toxic.
Insulting the duct with a fiberglass batt designed for the purpose is a good idea to cut down on losses and reduce condensation. The foil/plastic backed wraps both insulate and provide a vapour barrier. Use an aluminium metal duct tape to secure the insulation to the duct and seal any gaps.
The physical arrangement of the duct means you shouldn't get much cold air coming in; chimney effect is going to encourage warm air to leave instead of cold air coming in. Make sure the exterior flap is functioning to prevent air from blowing in. Often they will get blocked by insects or even mice.
posted by Mitheral at 5:24 PM on November 16, 2015 [2 favorites]
You shouldn't use a flammable material to insulate a hood duct. If the duct catches fire a flammable insulation can catch fire. Also polystyrene insulations need to be covered by a non-flammable layer in residences (in Canada anyways, your profile doesn't say where you are located) because the fumes given off when burning are toxic.
Insulting the duct with a fiberglass batt designed for the purpose is a good idea to cut down on losses and reduce condensation. The foil/plastic backed wraps both insulate and provide a vapour barrier. Use an aluminium metal duct tape to secure the insulation to the duct and seal any gaps.
The physical arrangement of the duct means you shouldn't get much cold air coming in; chimney effect is going to encourage warm air to leave instead of cold air coming in. Make sure the exterior flap is functioning to prevent air from blowing in. Often they will get blocked by insects or even mice.
posted by Mitheral at 5:24 PM on November 16, 2015 [2 favorites]
Response by poster: Thanks, all! The exhaust is 5" PVC pipe, so I will look for a circular flapper.
Mitheral - I don't even know what a batt is, so I will probably skip all that and leave the hood as is :-)
posted by cgs at 5:58 AM on November 17, 2015
Mitheral - I don't even know what a batt is, so I will probably skip all that and leave the hood as is :-)
posted by cgs at 5:58 AM on November 17, 2015
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I'm surprised about the maximum service temp of the foam insulation since polystyrene melts at 240C.
Our microwave exhaust has a flapper valve to cut down on back drafts. If you don't have one of those, that's honestly your best bet.
posted by plinth at 4:12 PM on November 16, 2015 [2 favorites]