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dkooda
January 21st, 2003, 12:18 PM
Hello,

Does anyone know how hot a normal electric dryer vent gets? I had my house sprayed with expanding polyurethane insulation and it's right up against my dryer vent.

The installer (of the insulation) said it's safe to about 180 degrees, but that sounded like a guess. He said it would be fine, but I have to have something to worry about <g>. Anyone have experience with this stuff?


Thanks in advance!

Dan Kooda

Wgoodrich
January 21st, 2003, 04:45 PM
High limit thermo in the dryer should be 200 degrees.

180 degrees should be maximum operating temp.

At the output of the dryer if you put a cooking thermometer in the exit vent of the dryer right behind the dryer then run your dryer on high temp about 15 minutes and take the temp reading. This should be the maximum normal temp output right at the dryer. The following are approximate temp statements. Once you leave 3 feet past the dryer whether in plactic or metal vent [both flexible plastic and metal vents are allowed to serve dryer venting] past 3 feet should have dropped about 25 degrees minimum.

I would say if plastic dryer venting is allowed then you insulating foam should fine also. I would say the thin plastic sheeting used in flexible dryer vents would be less than the 180 degree foam rating.

I would keep the foam a minimum of about 2 feet from the dryer in case of a malfunction and a fire did happen in the dryer due to plugged venting etc. Then the foam 2 feet away would not be available to feed the fire of an overheated dryer.

Hope this helps

Wg

jeff1
January 21st, 2003, 06:32 PM
High limit thermo in the dryer should be 200 degrees.



Hi all,

Just wanted to throw in my 12 cents worth ( Cruddy Canadian dollar! )

High limit thermostats in dryers can vary from as much as 200F - 325F depending on make, model#, age.

But, the average temp seen in the exhaust should be between 110F - 160F when the heat cycles on and off....average regular cycle temp is 135F - 150F.

jeff.

dkooda
January 22nd, 2003, 10:34 AM
I did a bit more research. According the fine folks at Whirlpool (very helpful, actually), they said the normal operating vent temperature (right behind the dryer) is 150 to 160 degrees. The high limit thermo is 250 degrees.

I guess the question is thus, considering the worst case scenario: How hot will the vent be at the point it meets the insulation, if the dryer overheats? I'll have an 7 1/2 foot vertical rise and a 8 foot run to the outside wall containing the insulation. It's probably another 12 inches or so to the actual vent outside. I'll be using non-insulated metal ducting, if that makes a difference.

If the temperature drops around 25 degrees after 3 feet, how much will it drop after 15 1/2 feet? Would it be safe to say it would drop 70 degrees?

Or, maybe that's not really the question. If the high limit thermo is inside the dryer, the normal operating temperature is probably much higher.

Am I being overly cautious?

Dan

Wgoodrich
January 22nd, 2003, 10:55 AM
It is odd you guys are coming up with these operating and limit settings. I have a 10 year old whirlpool dryer. The thermo disc for high limit is 200 degrees and the highest thermo cycling disc is 180 degrees. Temps must have changed over the years. I worked as a Sears service man from approximately 1969 through 1973. While designs may have changed I didn't notice the change. Seems the 325 degrees is pretty high for a high limit. May be true just seems high from past experience.

The person at whirlpool you talked to was he a salesman or service man?

I question your running your dryer vent straight up for 7 feet or more. If you can you should design your dryer vent to go down or straight sideways. Veritcle rise should not exceed approximately 3 feet or so.

Problem is a dryer venting has lint that goes out the vent as well as atomized moisture or steam. As this combined lint and steam travels along the vent pipe the temp coos rapidly allowing that moisture and damp lint to get heavy and fall in the vent tube.

If the vent is straight sideways or goes down then sideways then the lint most often exits the vent outside.

If the vent ran up as much as you say much of that lint will not make to the top bend thus falling back to the bottom of the vent pipe and building up eventually plugging that vent. A plugged vent prohibits air from cooling a dryer causing prolonged drying and overheated possibly scorched clothes. The overheating repeatidly invites a clothes dryer fire.

If you have a crawl space under your dryer you would be better served going down then out instead of up that far then out.

If you are concerned about heat of the vent pipe pull your dryer out. You should have used a flex vent from the metal vent pipe to the dryer for flexibility and ease of dryer installation. Run the dryer on high for about 30 minutes touching that vent hose behind the dryer. Doubt you will find a time that you can not hold your hand on the vent hose during that 30 minutes. The vent pipe does not get nearly as hot as you suspect.

YOu concern should be venting design to confirm you have not invited that vent to be plugged later as time goes by causing your dryer to overheat.

Just my experience and thoughts

Wg

dkooda
January 22nd, 2003, 11:34 AM
I talked to a service person at Whirlpool (I think it was called 'an interactive service center', or something). The guy on the phone didn't have the answers, but put me on hold and came back a few minutes later with the exact numbers.

I appreciate your thoughts on the vent. Unforntately, I don't think I have any other options. The laundry room is on the lowest level of my house. Two walls face other rooms, so they are out. Another wall has a high grade outside, so I'd be faced with a higher rise. The builder chose to put the vent on the remaining wall. To get above grade, the vent was placed at 7 1/2 feet.

The previous owner has his dryer on the adjacent wall and had the same rise, but used 3 90 degree bends. When I took that pipe down, I found it to be almost completely plugged.

For the past two years, I had a dryer directly under the vent. I had the same rise, but a much shorter run. With the help of this forum, I found I couldn't put my new dryer there, because it overlapped the main panel. To minimize my bends and turns (and still keep my washer in the vicinity of the dryer), I decided to put it on the opposite wall.

My old gas dryer was a real workhorse. In the two years I had it on that wall, I never had to clean the vent. It was over 30 years old and finally gave out.

Is there a vent that would have a lint collection area at the bottom of the rise? Something like a drip tube on a gas line? I suppose not, it would probably mess up the smooth flow of air to the outside...

Thanks

Dan

Dan

Wgoodrich
January 22nd, 2003, 02:23 PM
Dan according to the International Residential Code a screen is not allowed to be installed in this dryer vent duct. With the exceptoin of the flex hose from the dryer to the wall dryer duct the rest of the dryer duct must be metal and with the inside joints facing away from the dryer so lint does not catch on the joints. Also you must secure this duct with furnace tape and not screws. No screws are allowed to penitrate the metal dryer duct.

Hope this helps

Wg

jeff1
January 22nd, 2003, 06:22 PM
It is odd you guys are coming up with these operating and limit settings. I have a 10 year old whirlpool dryer. The thermo disc for high limit is 200 degrees and the highest thermo cycling disc is 180 degrees. Temps must have changed over the years. I worked as a Sears service man from approximately 1969 through 1973. While designs may have changed I didn't notice the change. Seems the 325 degrees is pretty high for a high limit. May be true just seems high from past experience.


Howdy,

I don't think too much has changed since '73...just different manufactures have different temps depending on thier design...I have found Frigidaire and Westinghouse to usually have the higher safety thermostats...but so has WLP...a copy...
**** Open / closed
L120 120 / 110
L125 125 / 115
L130 130 / 115
L135 135 / 120
L140 140 / 130
L145 145 / 125
L150 150 / 130
L155 155 / 135
L165 160 / 120
L175 175 / 135
L180 180 / 170
L190 190 / 150
L200 200 / 160
L205 205 / 165
L225 225 / 185
L240 240 / 200
L250 250 / 210
L260 260 / 210
L270 270 / 230
L290 290 / 250
L300 300 / 250
L320 320 / 270
L340 340 / 300

These are all WLP thermostats.

My own GE gas dryer has 225F safety thermostats and one 135F operating thermostat and a second operating thermostat at 145F.

**Also you must secure this duct with furnace tape and not screws**

Anybody else use that silver duct tape...man I love that stuff!! :)

http://www.applianceaid.com/images/venting%20a%20dryer.JPG

jeff.

Wgoodrich
January 23rd, 2003, 12:58 PM
Jeff,

Boy I would say you are on this subject. Your info is impressively complete. I seldom worked on other brands yet did to some degree. While the 225 limit does not suprise me too much you did shock me with teh 325 high limit. That just seems high to me concerning safety yet I am from old appliance shools, much can change. Glad your knowledge is available.

Keep it coming

Wg