Ventilation Required for Dryer, and occassionally with Exhaust fan and Water Heater

[smokiibear]

Fellows, As of recent, our local building departments are starting to require luevered doors and or makeup for laundary rooms that contain dryers. Per CMC 504.3.1 a dryer closet requires makeup ari of not less than 100 sq in. However, this section does not give any indication what size room constitutes a closet, and our building department seems to be pushing the limit of what a closet is.

Furthermore, when the dryer is present with an exhaust fan and/or a water heater, both of which draw air from the same space, conceiveably there could be a problem if the space is limited enough. I suppose then it is necessary to look at CMC Chapter 7, 701.4 for Combustion Air and Ventilation. 701.4.1, Standard Method seems way overkill. In other words, a laundary room would require a 14.7'x14.7'x8.16' room that has a few cabinets in order to provide 1750 Cubic Feet for a 35K BTU dryer.

How does one resolve what should be required for a dryer with option of having an exhaust fan and water heater? If it is Known Air Infiltration Rate Method, CMC 701.4.2, how does one determine the air changes per hour (ACH).

Any help would be greatly appreciated.

 

[willard3]

You need help from a senior HVAC person in your office.

 

[chicopee]

Add up the CFM for ventilation and the CFM's for proper combustion of dryer and of hot water heater and size that louver to that total CFM's. Assume all CFM's to be concurrent. The louver manufacturer would have technical data for sizing their product.

 

[dbill74]

Consult your AHJ for their definition of what constitutes a closet versus a room. I usually define a closet as being limited to containing just the laundry equipment, no room for sorting/folding table etc. If you have tables and such I consider it a laundry room.

Whether it is a "closet" or "room" doesn't matter, you will still need ventilation air. Dryers have an internal fan which can be supplemented with an external one if needed. The end result is you have a source of exhaust air driving the space negative. The 100 sq in. louver is to allow make-up air into the room; this assumes one dryer only.

If there is an exhaust fan supplementing the dryer's internal fan, the make-air louver needs to be sized to accommodate the EF's CFM.

When a gas fired water heater is in the same space as the dryer then you need to consider both dryer exhaust and combustion air requirements. It is safer to error on the side of caution and assume both will be operating simultaneously, thus you need to sum the air flows and provide adequate make-up air/louver free area for both.

If this is for a laundry mat with multiple dryers and heaters you can apply a diversity factor. How much of a diversity factor depends on how many dryers and heaters are present and the expected use.

One important note is that dryers and combustion water heaters need their air exhausted, meaning it has to go to the outside. The make-up air does NOT have to come from outside (at least per IMC, I assume CMC is similar), it can come from/transfer from adjacent occupied spaces. In the southeast USA and other humid environments this is preferred to keep humidity levels in the laundry closet/room at a level that does not encourage mold growth.

 

[berkshire]

One thing you have to be careful of, if you have a natural draft water heater in the same room as Clothes dryers , the air in the room must not go negative.
B.E.

You are judged not by what you know, but by what you can do.

 

[dbill74]

Negative to what B.E.?
Negative to outside? I agree with you.
Negative to adjacent occupied space, not so much.

 

[berkshire]

I meant Negative to the outside air, particularly where the end of that flue pipe is, You will end up with back drafting.
B.E.

You are judged not by what you know, but by what you can do.