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OT: gas dryer basics

CC.Rob Member Posts: 128
So what's the deal with gas dryers? Just saw one. Says 20k BTU/hr input, but no idea what combustion efficiency might be, whether it's fixed fire or not, etc.

And whether it's reliable and/or more efficient over the long haul than an electric.

Any insight appreciated. TIA.


  • Steamhead
    Steamhead Member Posts: 15,331
    edited September 2010
    A gas dryer

    exhausts its combustion products with the moist air leaving the drum. So the exhaust will have a considerable amount of excess air. But you can test for CO. In general, they fire at a fixed rate and turn the burner on and off to maintain temperature.

    Being relatively simple machines, gas dryers are pretty reliable. And in most areas they are cheaper to operate than electric dryers, since electricity costs more per BTU.

    Given the choice, I'd go with gas. Actually, that's exactly what I did when it was time to replace our old electric dryer.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Brad White
    Brad White Member Posts: 2,393
    Steamhead is right

    the dryer is 100% efficient for the reasons Steamhead stated; all input goes into the dryer.  The fuel cost depends on your area, but if you are spending say $2.20 per therm for gas, an hour with the dryer on will cost you 44 cents. (Actually half that because the burner cycles on and off, burning about half the time.)

    An equivalent electric dryer uses about 6 kW and at 18 cents per, depending on your actual rate, will cost you $1.08 per hour (or half that, assuming cycled control). But 44 cents to a dollar-eight speaks to me.

    One thing about gas and having the combustion products included in your clothing: There is a good bit of water vapor in the process. This is why when you tumble clothes to release wrinkles (Bachelor's Iron!), the moisture from the combustion process assists to relax the fabric. All the more reason to vent it.

    The key to happy drying though is airflow, you have to move it outside. If close-coupled to the exterior, great. If an interior dryer and ducted some distance, an in-line booster fan for the purpose is essential, not to mention a source of combustion air.  The point here is, do not restrict your airflow.

    And no starch please. :)
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    Something a lot of people miss

    concerning dryers is the need for make up air in the zone the dryer occupies especially if the heating and water heating equipment is located in the same area. Code actually specifies this requirement and even most inspectors do not know of the requirement.

    This is air in addition to air for combustion to replace the air being removed by the dryer. The dryer actually is considered as an exhaust not a vented appliance.

    Dryers actually should be isolated from other fossil fuel burning appliances in order for everything to work better.

    If there is a down side to today's gas dryers they are a nightmare to service. The access door to the burner that used to be on the front has gone away due to an accident with a child a while back. In some cases to service the dryer you have to remove the drum.
  • CC.Rob
    CC.Rob Member Posts: 128
    great stuff

    Wow. Thanks guys for the great perspectives. It's going in shortly.

    The guts do look simple (modular, anyway), and not impossible to access.

    The actual numbers pencil out pretty much as Brad described. Just a hair less favorable, but still impressive.

    The space in question has no other appliances requiring combustion air, and it will have plenty. And short, all rigid exhausting.

    Thanks again.
  • rlaggren
    rlaggren Member Posts: 160
    dryer vent material

    When running the vent hard pipe is best; the corrugated silver "snake" is dirt easy to run but reduces flow somewhat and collects lint. Not a big deal for a short run but as you approach 15-20' you want all the flow you can get; 20' is about the max run recommended w/out a booster fan.

    Besides requiring some thoughtful routing and cutting and assembly hard pipe has one disconcerting property - it leaks lint at every conceivable joint. When I install a dryer vent I tape _every_ joint with silver tape, including all the joints on any adjustable el's used in the run. I also tape the seam in the pipe - I purely hate to find lint piling up! Finally, technically you're not supposed to assemble the vent with sheet metal screws because the bit they protrude into the pipe collects lint; I don't know of any actual issues one way or the other but I've been "corrected" on this by a couple inspectors so I pass it on.

    Cheers, Rufus
    disclaimer - I'm a plumber, not a heating pro.
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    Correct no sheet

    metal screws in dryer exhaust pipe.
  • Brad White
    Brad White Member Posts: 2,393
    I second that

    MA Code and most codes, IMC, etc. prohibit any intrusive fasteners. Pop rivets are ok and probably the most intrusive thing I would use. But for our specifications, including commercial dryers, we specify Lindab and other gasketed duct and fittings. These fittings have twin rubber rings which seal well, yet come apart for inspection and cleaning. Of course cleanouts at changes of directions, (wye fittings so you can peer downstream) are essential. Just another way to comply with code.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
This discussion has been closed.