Question
We are in the planning stages of a new shop with showroom and (finally!) enough room to comfortably build, finish, stage and display. I am in east Tennessee and most of our winter is fairly mild. Coldest days are usually a low of 25 degrees. But the average winter temp is probably 40-45 degrees. I have searched the Knowledge Base and read a lot of posts about shop heating and I'm confused. I want to maintain a shop temp of about 60, a little higher in the spray room - probably 70-75 degrees.
There will be a small (I'm thinking 10'x7') area outside the main spray room, separated from the rest of the shop by a door, for the finish to flash off before being rolled back into the staging/hardware area. I want to control the shop heat, spray room heat and humidity, and dust. This building will probably be the last location and I want to make it as user-friendly as possible from the start. What are your considerations and suggestions for the most efficient means to heat this space? Should I use one means of heat for the main shop floor (maybe radiant in-floor) and something else for the spray room?
I'm not very schooled in air exchange issues, etc. Our spray room now is vented only with an explosion-proof fan and the spray area is open to the rest of the shop, so you can imagine the dust issues. I want to keep it separate as well as have space for the finish to flash off to eliminate dust problems. I have also thought about an open front type spray booth that would be in the back part of the spray room with a partition wall and opening to get the cabinets in and out of, then the whole thing partitioned off from the rest of the shop. Get me started, guys - I'm really lost on this.
Forum Responses
(Cabinetmaking Forum)
From contributor D:
I put in a Munchkin boiler in my shop last year. It replaced a forced air unit and it cut my heating bills in half over that 15-year-old furnace. I like it for a few reasons. It has a sealed burner, so it draws in fresh air from outside and exhausts outside, so there is no chance of explosion from inside vapors or dust, plus no filters to change.
It also has a variable output so that on warm days it may run with as little as 66000 btu and on those cold January Minnesota days, this model can go up to 199000 btu. There are also smaller units. I had no good way of doing radiant heat due to the existing shop configuration, so I found some old cast iron radiators for free and used them, but if I were building, I would not do it any way other than radiant heat.
In the booth, you can use the radiant heat too, and if you are spraying a lot, put in a make-up air unit. I have so far gotten by with just the boiler. When I know I am going to be spraying, I bump up the temp to 80 degrees in the morning and that gives me a buffer that allows the boiler to keep up.
A make up air fan pumps outside air into the space to make up the air exhausted by the spray booth exhaust fan. If the capacity (cfm), of both fans were exact, the pressure in the spray area would be neutral. By that I mean neither positive nor negative, the same as all other areas around the shop.
Your biggest concern along with venting the spray area is to keep dust and dirt from entering the finish area. To accomplish this, you need a slight positive pressure in the finish area. The make up fan needs to bring in more air than you are exhausting. (This air also needs to be filtered). When doors to the finish area are opened, air will flow out. The same applies to leakage of air around windows or other small openings to the surrounding space. If the finish area were in a neutral or negative pressure, dirt and dust would enter the area.
Fan pressures are measured in very small amounts. A pressure of 0.3 psi is generally sufficient to provide a positive pressure and keep out dirt and dust.
Just think about positive and negative pressures, and remember that air at a higher pressure will always try to flow to a lower pressure area, equalize, so pressures are equal. Like air in a balloon, the air inside is pushing against all sides of the balloon, attempting to get to the lower pressure outside. Also, remember that as air flows, dust and dirt flow with it.
This is pretty general information. I hope it helps!
Air should always be filtered before it enters a fan. Filters placed on a fan discharge create a resistance to air velocity and quantity, making the fan motor work harder. Depending on other factors, cfm can be reduced by amounts of 20% or greater. Also, this resistance to air flow overheats fan motors and causes a fan motor to draw more current, (power), resulting in more energy usage. Unfiltered air moving over the fan blades or squirrel cage over time will deposit dirt on the blades, causing further load on the motor and reduced fan performance. All of these conditions shorten motor life. For proper and maximum fan performance, the space being ventilated should be on the negative, (suction) side of the fan. Spray room air should move through the filters, into the negative side of the fan, then out the positive side of the fan to the outdoors.
Contributor R, I had thought about dehumidifying but never about cooling. We just always toughed out the hot weather. How do you accomplish this? Also, how do you control humidity in a heated environment? Just relying on the colder weather to be dryer?
Based on your first post, it seemed you might need some background and facts about fans and ventilation. My purpose was to give you a few basic and general facts about fans, fan performance, and make up air. Since retiring from a thirty-four year career as a mechanical engineer in HVAC, I turned my woodworking hobby into a small business. There isn't much I have to contribute here as a finish carpenter. You all know a lot more about that than I do. So, I was motivated at the opportunity to make a contribution in an area where I had much experience.
