Thread: Correct term for electric dryer air requierment

Just realized I'm uncertain as to the correct term for the air required by a non-combustion (electric) dryer... "makeup air?"

Also, is insufficient "makeup" air and efficiency issue only, or is a fire hazard as well? (This is an all electric condo unit, so I'm not concerned about backdrafting gas appliances).

Thanks

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As with any exhausting type appliance, make-up air is required so as to make up for the amount of air being extracted from the interior space and relieve the negative pressure which would otherwise occur.

Being as few, if any, dwellings provide for sufficient make-up air, the interior spaces go under negative pressure when exhaust fans, range hoods, clothes dryers, and the like, are operated. Cheap bathroom exhaust fans do not exhaust much, however, there should still be make-air provisions built-into the structure.

The only real problem is creating a negative pressure and drawing in unwanted moisture and other contaminates.

At least that is what I think I know. We'll see how much is wrong by other responses.

Tracked down what GE says....

(This is one of those times when I feel the need to justify my existence, this was about the cleanest condo ever seen, the only other issue I could find was a tub spout that dripped pretty badly when the shower diverter was engaged ("The horror. The Horror!")... the listing Realtor showed up up part way through the inspection and said the only defect found at the previous inspection was a "buzzing refrigerator" (seems it was a actual defect though, as replacing the compressor fixed it) so I suspect the previous inspector felt about the same.

A 1/2" Gap under the door (3.0) will allow 300 cfm

Originally Posted by Michael Thomas

Tracked down what GE says....

(This is one of those times when I feel the need to justify my existence, this was about the cleanest condo ever seen, the only other issue I could find was a tub spout that dripped pretty badly when the shower diverter was engaged ("The horror. The Horror!")... the listing Realtor showed up up part way through the inspection and said the only defect found at the previous inspection was a "buzzing refrigerator" (seems it was a actual defect though, as replacing the compressor fixed it) so I suspect the previous inspector felt about the same.

MT: Most, if not all, dryer manufacturers have similar requirements for their equipment. How many times do you actually see vents in a laundry closer to room door? I almost never do.

Originally Posted by Stephen Meyer

A 1/2" Gap under the door (3.0) will allow 300 cfm

While that may be true (I have no idea if it is or is not) that would not meet the manufacturer's installation instruction's requirements (as posted by Michael Thomas).

Originally Posted by Stephen Meyer

A 1/2" Gap under the door (3.0) will allow 300 cfm

Do you have a source for that info? That figure is about three times as high as I would have figured, even under some fairly high pressure differences between the two rooms.

Jim Brewer

Make up air, for dryer. Why not install a door with louver panels.

I another note, I seen door with a panel was cut out, and steel louver
grill panel was installed in its place, to allow make up air inside the closet and bathrooms.

Originally Posted by Jerry Peck

While that may be true (I have no idea if it is or is not) that would not meet the manufacturer's installation instruction's requirements (as posted by Michael Thomas).

+1

This was never a big deal until we started to stuff these stackable washer dryer combos in a 3x3 closet. I would think a louver door would be appropriate and would accept it all day long. In the CMC, which is modeled after the UMC which was written by the NFPA, it is addressed in section 905.3. They talk about two different Types of dryers in this section. A Type one is primarily used in a family living environment and may not coin operated; a type two is commercial or business use. Bottom line, in the CMC/UMC per section 905.3A, make up air provided for Type 1 dryers shall be in accordance with the manufactures’ installation instructions.

Originally Posted by Jim Brewer

Do you have a source for that info? That figure is about three times as high as I would have figured, even under some fairly high pressure differences between the two rooms.

Jim Brewer

Just a guess, but this is how I calc it.
36" wide door, * 1/2" = 18 Square inches of vent...
so that is the same as 4" x 5" vent hole in an air tight door (20" sq inches).
That hole is bigger than the exhaust hole for the dryer so it would be fine...

A 4" round hole is 12.5 sq inches.

--Personally I would do a 1", just in case someone added carpet and that 1/2" disappeared.
Code in my area is 1" min for door under cuts to avoid vents (36 sq inch vent= 6x6 vent = 3.6x10 inch vent).

Originally Posted by Ken Lyons

Just a guess, but this is how I calc it.
36" wide door, * 1/2" = 18 Square inches of vent...
so that is the same as 4" x 5" vent hole in an air tight door (20" sq inches).
That hole is bigger than the exhaust hole for the dryer so it would be fine...


--Personally I would do a 1", just in case someone added carpet and that 1/2" disappeared.

Except that usually there are minimum opening dimensions, such as 3" for the shortest side, to reduce restrictions.

And a 4" diameter hole in a door will not suffice to allow the same make-up air in as the dryer is pushing out that 4" diameter hole it is exhausting through - that is under much higher pressure.

Like Jim, I too would like to know how he arrived at that and what back-up documentation/information he has for it.

To abide by the manufacturers installation instructions you need 120 in² net free area, divided between the top and bottom of the door. (And by the way, that's the manufacturer's requirement for an electric dryer):



So you if you wish to meet those requirements by trimming the door , you need a 1.6" in x 36" opening, top and bottom.

It may be excessive, but that's what the manufacture requires, and I'm pretty loath to put myself in a situation where I'm telling the client to disregard the manufacturers written installation instructions on something it's arguably a safety issue.

Originally Posted by Michael Thomas

To abide by the manufacturers installation instructions you need 120 in² net free area, divided between the top and bottom of the door. (And by the way, that's the manufacturer's requirement for an electric dryer):



So you if you wish to meet those requirements by trimming the door , you need a 1.6" in x 36" opening, top and bottom.

It may be excessive, but that's what the manufacture requires, and I'm pretty loath to put myself in a situation where I'm telling the client to disregard the manufacturers written installation instructions on something it's arguably a safety issue.

There you go..

OK, first the reason:

SECTION 504
CLOTHES DRYER EXHAUST

504.1 Installation.

Clothes dryers shall be exhausted in accordance with the manufacturer’s instructions. Dryer exhaust systems shall be independent of all other systems and shall convey the moisture and any products of combustion to the outside of the building.

And now the requirement:

504.5 Makeup air.

Installations exhausting more than 200 cfm (0.09m3/s) shall be provided with makeup air. Where a closet is designed for the installation of a clothes dryer, an opening having an area of not less than 100 square inches (0.0645m2) shall be provided in the closet enclosure.

That is the extent of the 2003 International Mechanical Code pertaining to residential dryers.

As a municipal building inspector this is what is required at the time of the original installation or construction. I hope this helps.

Originally Posted by Ray Norton

As a municipal building inspector

Ray,

Welcome to the board.

"As a municipal building inspector" you also know that you are quoting the IMC and not the IRC, and that the IMC is not applicable to one- and two-family dwelling units and townhouses, right?

Ray: Welcome to the board, now DUCK!

Thanks Jerry and A.D.

Yes I am aware of that. I offered it up as help in determining what to do if instructions are not available to us when we inspect existing installations.

The IRC does not address make-up air. Typically when a code is silent on a subject it is considered allowable. But the manufacturer's instructions must be followed. So, I just wanted to share the reason make-up air is required and a standard that helps us when we lack the required information.

I'll be more specific in my future posts.

I am very happy to see home inspectors that are knowledgeable of the code.

Ray,

Some of us are also code inspectors or have been code inspectors.

We can always learn from others, regardless how much or how little we know. Collectively we know much more, and individually we learn from that collective knowledge base.

Originally Posted by Ray Norton

Thanks Jerry and A.D.

I'll be more specific in my future posts.

I am very happy to see home inspectors that are knowledgeable of the code.

Ray,
Welcome to the board, and be prepared to be re-educated on the things you thought you knew. These guys are not only pretty well versed in a variety of codes; they can debate the meaning of "is" until you're pretty sure "is" means a color between "skunk" and "Thursday".

tc

I'll be more specific in my future posts.

RN: In this dδjō that is the mantra.

Originally Posted by archivoyeur

they can debate the meaning of "is" until you're pretty sure "is" means a color between "skunk" and "Thursday".

I thought that was "Thoisday". n'yuk, n'yuk, n'yuk

Originally Posted by archivoyeur

Ray,
Welcome to the board, and be prepared to be re-educated on the things you thought you knew. These guys are not only pretty well versed in a variety of codes; they can debate the meaning of "is" until you're pretty sure "is" means a color between "skunk" and "Thursday".

tc

Peeper Boy: Wow! This is Friday! I thunk is was Skursday!

Thanks Arch,

It seems this is going to be a very positive experience. I welcome constructive criticism and am constantly honing my abilities. Having spent most of my career "being inspected"; experiencing a wide variety of inspectors (good, bad and "it's my way or the highway" type) I believe accuracy, professionalism and accountability are of the utmost importance for inspectors.

I believe accuracy, professionalism and accountability are of the utmost importance for inspectors.

RN: So do we.

I have been a member for several months and must say that viewing the q@a on here has been a real learning experience. I am new to the home inspection field and don't have the experience in the building industry as most of the folks who post and respond on this site.
Frankly I am almost afraid to post a question as I think most of you will wonder why I got into the game at all. That said,I will continue to read and learn from all of you and I hope that if I post a question in the future you will cut me some slack and know that I am trying to learn as much as I can just like you. In the mean time I will sit on the sidelines and soak up your experience and wisdom.

ardent observer

Originally Posted by Gary wellborn

I have been a member for several months and must say that viewing the q@a on here has been a real learning experience. I am new to the home inspection field and don't have the experience in the building industry as most of the folks who post and respond on this site.
Frankly I am almost afraid to post a question as I think most of you will wonder why I got into the game at all. That said,I will continue to read and learn from all of you and I hope that if I post a question in the future you will cut me some slack and know that I am trying to learn as much as I can just like you. In the mean time I will sit on the sidelines and soak up your experience and wisdom.

ardent observer

GW: Just close your eyes and picture yourself growing very thick skin; almost like Kevlar. Now again picture yourself not taking offense to any of the slings and arrows that folks will let fly in your direction should you ask a question here. They are just words in cyberspace and cannot harm you.

Now that you are properly outfitted, go ahead and ask away. You have nothing to lose and an education to gain.

Gary,

In addition to what Aaron said, keep in mind that YOU know things WE do not ... so DO NOT hesitate to jump in.

Thanks for the advice and I am sure I will have cause to ask a few questions in the near future. Do any of you have experience in Thermography used in Home Inspections? I have found it is nice to have in many instances.Thanks again for the posting advice.

GW

Originally Posted by Gary wellborn

Do any of you have experience in Thermography used in Home Inspections? I have found it is nice to have in many instances.

I agree.

I bought my infrared camera in November 2004 (I think) and took my Level I class in January 2005, and used it at all inspections until I retired, then I sold my camera (for a fraction of what I paid for it, and I now wish I had kept my camera - oh, well).

Per ASHRAE 62,2-2007, all mechanical exhaust are required to have balanced MUA. This could be a slave switch or current sensing switch that energizes a power MUA ventilator to pump back into the house what is being exhausted. As for the size grilles, you have the mfrs. listed instructions first. Also, it plain must work. A gas dryer in a closet would be a "confined space" and subject to those MUA requirements. However, you would also need to check the listing for approval for installation in closets or alcoves and any special requirements such as the one Michael provided.

As to what problems could be caused by a lack of MUA: Fire! If you do not have the requisite airflow through the appliance, the internal temps will rise as will vent temps. With insufficient airflow into the compartment, you could get untoward heat signature in the appliance causing either heat related component failure or ignition of lint. I've seen melted wiring from a closeted dryer. Now, add a 1/2" of lint to the vent. You just reduced the flow capacity by just about the cube root. That's a lot. With the combustion chamber at the same firing rate with markedly reduced airflow (which in a gas dryer provides combustion air, dilution, excess air and cooling air), you have markedly higher appliance and vent operating temps. At the very least, it will take longer to dry clothes or more than one cycle, which will consume excessive energy. If the MUA is severely restricted, the blower motor can burn out from the low static pressure.

To calculate a CFM across an orifice, you would need to know the pressure gradient and actually air temp. Keep in mind there is a lot of turbulence in the corners and at any louvers or vanes, which markedly reduce effective air flows. That's why those severe penalties in the gas code for louvers and why you don't count the cold corners in chimney flues in the effective flue area. Actually, there is a boundary layer of air (static pressure) that does not contribute to airflow but rather restricts it. In a conduit, you can measure the CFM with a manometer, pitot tube and thermometer. In a larger opening, an anemometer is often used. However, both have inherent inaccuracies and require a little training such as doing a duct traverse for a grid of pressure readings.


Now, where's that plastic vent slinky?

Welcome Ray!

Bob Harper, most interesting post on gas dryers.

So with gas dryer in closet enclosure, keep the door open while in used?

But the larger the room area, the better the gas dryer will operate, even
with the room area door or doors closed?

Originally Posted by Robert S. Mattison

keep the door open while in used?

I saw many house here open a 8" or 6" dia. hole on the exterior wall called "Fresh Air Intake" in the laundry room, by the gas fireplace or in the wok kitchen. (Sometime called spicy kitchen, it is a small second kitchen mainly with sink and stoves separated with the main kitchen by a door. That is very common in Vancouver BC which is designed for Asian cooking, always equip with a hood fan of 600-1200cfm and gas stoves.)

Daniel Leung

8' or 6" Dia. hole on exterior wall call a, "Fresh Air Instake".


Perhaps, if your able, could post a MFG. listing for this product you saw.
Or better yet, an E-mail address link to the company.


Thanks for your post, and sharing some photo's.

Originally Posted by Robert S. Mattison

Bob Harper, most interesting post on gas dryers.

So with gas dryer in closet enclosure, keep the door open while in used?

But the larger the room area, the better the gas dryer will operate, even
with the room area door or doors closed?

What Bob said about those closets apply to ALL rooms and spaces, always has (and has applied to those closets with gas dryers too).

Most residential gas clothes dryers are rated 22,000 Btu/hr and if the room or space is smaller than 1,100 cubic feet then make up air is required, and the code addressed that in several options.

The 1,100 cf of space is the result of the requirement for 50 cf of space for each 1,000 Btu/hr, reducing the formula to its simplest form and you simply divide the Btu/hr input rating by 20, or, simply drop the right hand "0" and divide by "2" ... 22,000 = 2,200 / 2 = 1,100 (my KISS method, makes it real easy and quick to determine the cubic feet of space needed.

Let's say you have a laundry room with a gas dryer and two 75,000 Btu/hr gas water heaters: 22,000 + 75,000 + 75,000 = 172,000 = 17,200 / 2 = 8,600 cf of space required.

Let's presume that laundry room is 20 feet x 20 feet (which is a decent sized laundry room) and the ceiling is 10 feet high: 20 x 20 = 400 x 10 = 4,000 cf of space ... less than half of what is required for that not to be considered confined space, which means that laundry room, as large as it is, still needs make up air for combustion.

And that is just for the combustion make up air, not the air being exhausted by the dryer.

At first glance you probably would have thought that 20' x 20' x 10' high ceiling room would have been "no problem", right?

Originally Posted by Daniel Leung

I saw many house here open a 8" or 6" dia. hole on the exterior wall called "Fresh Air Intake" in the laundry room, by the gas fireplace or in the wok kitchen. (Sometime called spicy kitchen, it is a small second kitchen mainly with sink and stoves separated with the main kitchen by a door. That is very common in Vancouver BC which is designed for Asian cooking, always equip with a hood fan of 600-1200cfm and gas stoves.)

That might work for make up air for the exhaust air, but not for make up combustion air.

Originally Posted by Robert S. Mattison

Perhaps, if your able, could post a MFG. listing for this product you saw. Or better yet, an E-mail address link to the company.

RSM, here are some mfr. links:
Furnace fresh air intake vent - Ultimate Vent - combustion air vent
Fresh Air Intake Wall Vents With Screen
Air Vent Valve, Air Diffusers, Hvac Parts, HLM6305