Clothes dryer temperature measurements:

This article describes field measurements of a gas powered clothes dryer temperatures in the dryer and in its exhaust vent system.

This article series on clothes dryer temperatures gives the normal operating temperature at different points inside the clothes dryer appliance and its venting system. We include also unsafe temperatures that might be reached during various dryer faults or conditions and temperatures that could cause a dryer fire.

Page top image: the author [DF] measuring the approximate surface temperature of the hot air inlet of a Maytag LP gas fueled residential clothes dryer. With the dryer heat set to high and the gas burner on and stabilized the temperature was approximately 140 °F (60 °C).

Gas Clothes Dryer Actual Temperature Measurements

In July 2017, using an Exergen infrared thermometer I [DF] measured surface temperatures at key locations inside of a recent (2015) model Maytag Model MGDC21EW1 LP gas fueled clothes dryer installed in a home in Poughkeepsie, NY in May 2016.

I also measured the aluminum clothes dryer exhaust vent pipe surface temperatures at an indoor location close to the dryer exhaust outlet and outdoors inside of the metal dryer vent at the dryer vent screen.

[Click to enlarge any image]

Gas Dryer Temperature Measurement Conditions

• Measurements made at 4PM on 17 July 2017. Weather was hot and sunny.
• Estimated flat-roof cavity temperature - passage of the dryer exhaust vent (approximately 3 m) - 100 °F (38 °C)
• Approximate indoor ambient temperature - 72 °F (22°C)
• Approximate outdoor ambient temperature - 86 °F (30 °C)
• The dryer heat setting to HIGH
• The dryer in operation for at least ten minutes before measurements
• The gas burner was cycled on during measurements except for screening measurements made to demonstrate that the exhaust temperature falls whenever the gas burner cycles off
• For one temperature measurement close to the dryer vent attachment point, the surface measurement spot on the metal dryer vent was colored with black magic marker
• All other temperature measurements were made as close as possible to the measured surface but without having colored-black the measurement point
• The dryer tumbler drum was empty during these measurements - effects of wet clothing normally in a clothes dryer early in its cycle will not be shown but this measurement condition should be similar to clothes dryer temperatures at the end of a clothing-filled clothes dryer cycle.

Field Measurements of Clothes Dryer Operating Temperatures
Measurement Location	Temperature	Comments
Dryer interior / surface temperatures, gas burner ON
dryer tumbler drum surface	128 °F (53 °C)1	Dryer temperature set on HIGH, empty of clothing, stable temperature (Day 1)
hot air inlet to the dryer tumbler drum	142 °F (61 °C)1	same as above
hot air exhaust port	137 °F (58 °C)1	same as above
dryer front access door surface	103 °F (39 °C)2	Dryer temperature set on MEDIUM, normal load of clothing, stable temperature (Day 2)
Dryer exhaust vent surface temperatures, gas burner ON
Metal vent pipe surface 8" from dryer's rear exhaust port	123 °F (51 °C)1	Dryer set on HIGH, empty of clothing, stable temperature
Metal vent pipe surface 8" from dryer's rear exhaust port	103 °F (39 °C)1	Dryer temperature set on MEDIUM, normal load of clothing, stable temperature
Wood trim surface temperature adjacent to exterior wall dryer vent opening screen	86 °F (30 °C)1	(Day 1) Dryer set on HIGH, empty of clothing, stable temperature
Wood trim surface temperature adjacent to exterior wall dryer vent opening screen	88 °F (31 °C)2	(Day 2) Dryer temperature set on MEDIUM, normal load of clothing, stable temperature
Measured roof surface temperature	150 °F (65 °C)1	(Day 1) Black EPDM flat roof, hot sunny weather, roof surface in sun, range: 127 °F (38 °C) & 150 °F (65 °C)
Estimated roof / ceiling cavity temperature through which dryer vent passes	150 °F (65 °C)1	(Day 1)
Measured roof surface temperature	87 °F (31 °C)2	(Day 2) Black EPDM flat roof, hot sunny weather, roof surface in shade
Estimated roof / ceiling cavity temperature through which dryer vent passes	87 °F (31 °C)2	(Day 2)
Clothes dryer vent interior surface temperature at the exterior wall vent screen	143 °F (62 °C)1	(Day 1) Probably influenced by roof / ceiling cavity temperature
Clothes dryer vent interior surface temperature at the exterior wall vent screen	134 °F (57 °C)2	(Day 2) Dryer temperature set on MEDIUM, normal load of clothing, stable temperature
Notes: 1. (Day 1) Clothes dryer temperature was set on HIGH, dryer empty of contents, operating at stable temperature, measurement conditions: NY, hot July afternoon DESCRIBED ABOVE 2. (Day 2) Clothes dryer temperature set on MEDIUM, dryer with full load of damp clothing, operating at stable temperature, measurement conditions: NY, hot July mid-day, roof over dryer vent/ceiling in shade 2017/07/19 Poughkeepsie NY USA, outdoor ambient temperature 80 °F (27 °C), sunny conditions. 3. Measurements were made using a hand-held Exergen™ microscanner™ D-Series infrared scanning device shown in photos below.

The surface temperature of a solid metal clothes dryer vent approximately 8" from the dryer's bottom exhaust outlet port was 123 °F (51 °C) - photograph above

Above: measuring the outdoor temperature of the wall surface temperature near the dryer vent screen - 86 °F (30 °C) - photograph above

Below: measuring surface temperature of the dryer vent interior bottom 3-5" inside of the dryer's exterior vent screen - 143 °F (62 °C) - photograph below

Since heat always flows from the hotter into the cooler medium, and because I found higher temperatures at the wall exhaust point than at the dryer bottom exhaust point, I speculate that high roof cavity temperatures through which the clothes dryer vent exhaust is passing explain the higher vent temperature at the exterior wall.

At CLOTHES DRYER TEMPERATURE vs CLEARANCE DISTANCES you can see the passage of the dryer's exhaust vent through the building roof cavity during original construction / installation of the vent.

Discussion

Clothes Dryer Temperature Test Conditions: exhaust vent

The standard-diameter 4-inch clothes dryer exhaust vent materials are all solid-metal. During installation of this vent we excluded screws that might protrude into the vent interior and we taped its joints with foil tape. The total vent length is approximately 16 ft. and involves 4 90 degree elbows.

At this installation the clothes dryer vent passage and conditions are described as follows:

1. extends from the bottom of the dryer through an interior partition wall (about 6" total thickness including framing and drywall),
2. passes through a 90 degree elbow
3. extends upwards 7ft 6in on the exterior of a utility room wall (utility room interior temperature about 80 deg)
4. passes through a second 90 degree elbow to re-enter the wall, a third and fourth elbow to pass up, then horizontally through the ceiling of the laundry room
5. extends 8 ft. 2" horizontally passing straight through the interior of the insulated (open cell foam) laundry room ceiling
6. passes through the building's exterior wall at the rim joist (about 6" total thickness) to the exterior where a plastic louvered vent cover is mounted. provided by the manufacturer: this component causes rapid lint-clogging of the vent system.
7. The vent screen had been previously cleared of any blocking lint.
8. The dryer vent had been in light use approximately 14 months and sported a thin coating (1/16-1/8") of lint.

The laundry room ceiling (item 5 above) is framed with 2x10 lumber, insulated with 9 1/2" of open celled spray foam. The dryer vent passes through this space.

Photo above: the clothes dryer vent passage through the laundry room ceiling before insulation was installed.

Photo below: normal lint accumulation in the clothes dryer vent system after six months of moderate usage.

The dryer vent screen installed on this dryer vent system is discussed at CLOTHES DRYER VENT TERMINATION & SCREENS

Accuracy of Measurements of Clothes Dryer Temperature

Photo: interior of the tested Maytag LP gas fueled clothes dryer during conversion of the dryer from natural gas (factory set-up) to LP gas (field conversion). The tumbler drum, drive belt, and other components have been removed to give view of and access to the gas heating unit in the dryer. [Click to enlarge any image]

It is important when measuring temperatures in a gas fired clothes dryer system to note when the gas burner has cycled -on . The burner in this gas dryer model is not on continuously as the dryer spins. Rather the burner is turned on and off to keep the dryer within a set-temperature range as the dryer operates. It's easy to know when the gas burner is on:

• You will hear the burner cycling on and off
• During temperature measurement at a fixed location temperature will rise to a stable high when the burner is on and will fall to a fairly stable low when the burner is off.

Because the IR scanner is measuring the surface temperature the emissivity of the particular surface or conditions that effect its emissivity have an effect on the accuracy of the measurement.

For more accurate results, Exergen recommends that the user apply a black crayon or marker to a spot of a size larger than the area being measured by the scanner. I used this method only where the black spot would not cause complaints from the homeowner - that is, inside of a utility room at the dryer vent duct near the bottom of the dryer. Other locations such as the dryer interior were not blackened.

The result of measurements of a surface that was not blackened, when measuring dryer or dryer duct metal surfaces in the dryer's operating temperature range between 120 - 150°F (49 - 66°C) I observed readings that were usually 7-12°F lower than on blackened high-emissivity surfaces.

I think that the temperature sensor's close proximity to the vent interior surface and dark colour of the interior of the dryer exhaust vent (lint-coated with gray lint) may have made those measurements more-accurate.

More-scholarly and accurate clothes dryer temperature measurements using direct-contact temperature sensing devices were performed by Bonaccorso (2012) cited at CLOTHES DRYER FIRE RESEARCH.

Conclusions

The gas fired residential clothes dryer actual field-installation measurements made at a single dryer during hot weather in New York in July, 2017 produced results similar to the theoretical and laboratory results and conclusions of Bonaccorso et als (2012) and other experts. All of the temperatures remained well below the recommended maximum temperature inside the clothes dryer of 200 °C (392 °F).

One surprise is worth further investigation: the clothes dryer vent temperatures just inside the dryer vent at its exterior wall outlet were considerably higher 143 °F (62 °C) than even the temperatures measured at the dryer vent near the point of connection of the vent system to the clothes dryer where we found an outlet temperature of 123 °F (51 °C).

It seems possible that high temperatures in the flat-roof/ceiling cavity develop during sunny July weather at this building. The roof is covered with black EPDM rubber and has surface temperatures on hot sunny days ranging between 120 - 150°F (49 - 66°C) or higher. Longer periods of direct sun will produce higher temperatures on the roof surface.

I suspect that high roof temperatures contributed to the high clothes dryer vent temperatures measured at the wall exhaust. Below is an example roof surface temperature made after about 30 minutes of direct sunlight at the roof area in question.

Clothes dryer temperature & venting safety standards might consider the possible effects of the surrounding environment if the dryer vent passes through very hot spaces.

Also see DEFINITION of HEAT FLOW DIRECTION

Clothes Dryer Exhaust Vent Installation, Dryer Temperatures, Dryer Fires Research

Citations mentioned in this article as well as additional clothes dryer operation, temperature, fire hazard research material has moved to CLOTHES DRYER FIRE RESEARCH

...

Continue reading at CLOTHES DRYER SAFETY CHECKLIST or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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