View Full Version : Range Hood
Does anyone know why it is nearly impossible to find a house with a range hood that vents outside in it? I just bought a house in the Fayettenam/Raeford Metroplex and it has a microwave with a vent built in. This is the third place I have resided in that has this absurd feature. In most cases all it does is blow the exhaust in your face or onto the cabinets above. This is beyond irritating.
Dozer523
06-22-2012, 06:56
I think with microwave ovens the vent has more to do with the cooling fan.
Not a building contractor - or county code enforcer but........
Back in the old days of Ranch homes the vent hood had a straight run up and out exhaust. Look in the cabinet above the stove and there was the big old pipe. Some homes with the stove on the exterior wall had a short pipe with a 90 degree turn out the side wall.
Nowdays the kitchen is more towards the interior with a snack area by the exterior wall. Exterior venting would require longer runs which means more space. And then there is two story homes.
I would expect - with the amount of grease that builds up over time in my micro wave vent - any long run system could get pretty guncky over time and be a good place for bugs to hide out in. Be a mess to clean that out.
Generally many current microwaves are set up to adapt to either external venting or interior through a filter. Generally speaking, most of the mountable appliances I see are vented inside just as yours.
Exterior vents (hoods, cook tops or microwaves) require that they be vented to the exterior of the dwelling, not the attic, not a wall or floor cavity. Proper ventilation requires duct work and a penetration through the roof or a exterior wall. If you have a multiply story house and/or a large house exterior venting my not be an option because the length or height of the duct would exceed the capacity of the fan.
That can be quite expensive and time consuming.
Or you can switch the vent plate around for interior venting. Venting inside just requires mounting the device, plugging it in and you're done.
So it comes down to home design, ease and cost effectiveness for the builder or previous homeowner.
IMO.
longrange1947
06-22-2012, 13:43
Think energy efficiency and think about the expense of having an energy efficient vent to the outside along with all the others that are mandated. :munchin :D
My home built in 72, originally had a range hood which was vented through the roof via 8" pipe at a point approximately 10' above the ground. I replaced the hood with an over-the-range microwave (extra cost item). It uses the same exhaust fan, and filters that the the internal exhaust system uses. The top of the micro is about 68" above the floor, so the total length of the vent pipe is about 4.5 feet. Been living here more than 24 years and have never had a problem with grease build up. Both internal and external vent reqiure the use of grease filters (washable) which need to be cleaned on a regular basis , with the interval depending on how much frying you do on your range.
Think energy efficiency and think about the expense of having an energy efficient vent to the outside along with all the others that are mandated. :munchin :D
To my knowledge, most, if not all microwaves use the same fan motor, for internal or external venting.
BTW, if it's not externally vented the use of a recirc air charcoal filter (some cost about $50) that needs to be replaced every 6-9 months (depending on frequency of use) is required.
IMO external venting is the way to fly!
I think with microwave ovens the vent has more to do with the cooling fan.
Not if its an over-the-range model. External venting is for the range (exhaust fan ) hood function (when cooking on the range), not for the operation of the microwave itself.
mark46th
06-22-2012, 21:40
The last one I installed had an option of venting out the front of the Microwave or opening up the back of the oven and redirecting the duct upwards to the vent....
Here is the current code and the highlight is the opt-out.
M1503.1 General.
Range hoods shall discharge to the outdoors through a single-wall duct. The duct serving the hood shall have a smooth interior surface, shall be air tight and shall be equipped with a backdraft damper. Ducts serving range hoods shall not terminate in an attic or crawl space or areas inside the building.
Exception: Where installed in accordance with the manufacturer's installation instructions, and where mechanical or natural ventilation is otherwise provided, listed and labeled ductless range hoods shall not be required to discharge to the outdoors.
Here is a good example of confusion on the subject of range hoods and ventilation....among inspectors.
http://www.inspectpa.com/forum/showthread.php?7394-IRC-Ventilation-of-range&
And this is what they are debating:
http://publicecodes.citation.com/icod/irc/2012/icod_irc_2012_15_sec001.htm
Golf1echo
06-25-2012, 05:59
Good answers above. Mostly cost and convenience. The perspective of the appliance manufacture comes into play also, they generally want their products to go into as many applications as possible.
With vent runs it requires more power than you might think and keep in mind fans pull better than they push.
The energy considerations do play a big part. If you left a fan vented to the exterior on it could suck out lots of cool or warm air.
Keep in mind with commercial design HVAC systems work with air pressures ie: more pressure at dinning areas and less in kitchen and restroom areas. This send undesirable gasses to where they can be vented and resupplies fresh air to where patrons are as health concerns would dictate. Many times venting occurs above the ceiling plane.
Thanks for the info guys. Trying to get used to my microwave vent and the window.
If you do decide to re-install ventilation, I would inquire about the place of manufacture. I worked for a manufacturer of Swedish dishwashers, washers and dryers in the Dallas area for about three years and one of the companies that the mother conglomerate acquired was Antonio Merloni based in Fabriano, Italy. I visited the factory once and saw one assembly line and at the end of the line, 30 different name brand badges could be applied. The quality control was the weakest point and eventually led to the bankruptcy of the Italian conglomerate and ultimately the breakup and demise of the company. Fabriano is such a little town that everyone in town is involved in appliance manufacturing.
I have since learned that the Merloni corporate entity resurfaced after the bankruptcy and are again churning out well thought out, innovative designed but poorly inspected pieces of crap just as before. However, this iteration has no American based company to do the warranty bailouts with regular infusions of American investment dollars.
Research and stay away from pretty yet unreliable Fabriano made ventilation products.
I can get away with bad mouthing this company because I was once on the inside and also, that company sank in the 2007 meltdown.
1. With vent runs it requires more power than you might think and keep in mind fans pull better than they push.
2. The energy considerations do play a big part. If you left a fan vented to the exterior on it could suck out lots of cool or warm air.
1. I've owned 4 or 5 OTR microwaves and all of them used the same exhaust fan motor whether they were installed with external venting, or used in the recirc mode. So how can it require more power. The fan is pulling the same hot moist (and sometimes greasy) air off the range top when either operating in the vented or recirc mode.
2. If the HVAC system is operating in the AC (cooling) mode, then the externally vented range hood is reducing the amount of hot wet air the HVAC must cool and dehumidify to keep the house comfortable. It costs far more to do that than it does to run the fan motor of the microwave. Remember we are talking about a home kitchen here, not a commercial kitchen. The cfm of air removed by a microwave range hood is miniscule.
BTW, hot moist air recirculated into the interior of the house promotes the growth of mold. IMO, the benefits of venting far outweigh any negatives.
If your vent run is more than you want you can also install a midline booster fan. The best ones are American made in Michigan and can boost the throughput of your moist greasy air.
I have been through this with my wife. She insists on turning on an over the range fan that just sends the smoke out into the kitchen instead as outside.
Golf1echo
06-27-2012, 19:38
WCH
1) To be more specific: If longer runs are required to vent to the exterior you would need larger vents and bigger fan to get that accomplished efficiently, similar to hydraulics ( movement of liquid ). Fans don't generally use that much electricity but I doubt a fan built into the micro wave would effectively push air that far down any vent. More than likely you would use a vent fan at the exterior if there was much of a run.
2) You are right about venting undesirable air out of the living environment to prevent problems the trouble is if left on it would vent more conditioned air out than you might realize. In HVAC design it is important to consider where losses occur. Take the cooling you mentioned, in a warm climate we look at things like the treatment between the bottom plates and the pad or deck. I would make sure I sealed that detail well with some kind of foam or sealant because cool air sinks and can be lost through any cracks or openings. The BTU losses are significant on untreated bottom plates and it all adds up over time and the accumulative openings. You can calculate what kind of losses you would have depending on the fan output. These issues are less important in homes where energy efficiency is not a priority.
WCH
1) To be more specific: If longer runs are required to vent to the exterior you would need larger vents and bigger fan to get that accomplished efficiently, similar to hydraulics ( movement of liquid ). Fans don't generally use that much electricity but I doubt a fan built into the micro wave would effectively push air that far down any vent. More than likely you would use a vent fan at the exterior if there was much of a run.
It would have to be one hell of a big house to need more than the standard motor/fan. GE specs say not to exceed the equivalent of 140 ft using either 3-1/4 x 10 inch rectangular or 6" round duct. My house has 8" round duct venting straight up thru the roof. Hot air rises, so how hard does it need to be pushed?
If the micro is installed without being vented, the recirc air must be pushed through a charcoal filter (adds friction and cost).
I'm off to bed....
Golf1echo
06-28-2012, 06:36
Sounds like your 8" vent is going straight up and out through the ceiling, that is a good size vent. Situations vary from house to house if one could not go straight up and out you would need a 9" wall to enclose that same vent or go rectangular, if bends or a slanted horizontal venting was needed they all add resistance. You are also getting a tug from the top as air passes or turns your vent cap. Whats for breakfast?
My system is a recirc system. I have a window in the kitchen which apparently is to aid in this issue I despise. After looking, it seems to suck the air off the range, through two roughly 3"x5" filters under the microwave then blasted out an exhaust at the top of the microwave, directed slightly away from my cabinets and my face. I have yet to experiment with greasy or smoky cooking (I think thats a good thing) but as soon as I do Ill post appropriate results.
Greasy cooking complete.....Results? I am about to knock a hole in my wall for a vent system that is worth a damn.