shop HVAC

[brenthenze]

There's been a lot of discussion lately about dust control, and I have a question somewhat related to that. In my new building (which is stand-alone and will be insulated), I'm going to need to have some sort of heating and air conditioning--either window a/c units and space heaters or an installed system.

Initially I'd planned to use window units for the first year, just to see how much I needed, and then--if needed--put in an HVAC. However, for a couple reasons, I'm now thinking it might be smarter to install an HVAC system right from the start. I don't have any insulation or wallboard in place yet (or even any electric), so it'd be comparatively easy to install something now rather than later. Plus, if I do window units, I'd have to install double-hung windows. That had been my plan initially, but I'm now thinking that I may just build casement windows rather than double-hung. The window openings are relatively small (so as not to take up too much wall space, and also because small windows look more architecturally appropriate in a traditional barn), and double-hung windows would be overkill. The only advantage of double-hung is that I could use a window a/c, yet if I do that, I'm sacrificing natural light. (Yes, I should have built bigger window openings, architecture be ****ed!)

So, assuming I go with HVAC from the start: do y'all just use regular home HVAC systems, or is there something that's specific for woodshops? I don't want to spend $1500 on an HVAC setup, then kill the thing because of dust. I'll get a DCS eventually, but even with a good DCS, I assume there's still enough dust floating around in a workshop that it'd quickly clog a traditional home HVAC system. Or am I wrong about that?

I'll talk to an HVAC crew abbout this, too, of course, but I'd like to know what's standard among woodworkers before I talk with a sales guy who might want to sell me more than I need. Is there somehting specific I should be asking for?

Brent

 

[RayH]

Brent,

Congratulations on the new shop to-be. HVAC makes all the difference in the world.

I'm don't know of any "standard" in use, although many seem to use window units. Cost and the "add-on" nature of heating/cooling an existing unconditioned space seem to be the general reasons.

Given that you can stand the increased cost, I would suggest other alternatives. A central, "split" system is my choice.

The central system generally carries a 5 or 10 year warranty on the major components. It also can heat and cool evenly without the noise or wind of a window type unit. IMHO a central unit also offers you a host of options to use it as part of a dust control system. Add lots of standard pleated filter surface area in the air returns and locate them (and the air inlets) with dust control in mind. You can do much of the work by boxing in standard returns so that you triple, or more, the filter area.

Hope this is helpful. I already envy you your new shop. Just imagine being to put your windows where you want them.

 

[Charles Lent]

I have a small shop (14 X 26) that is moderately insulated, and have had a window style 24,000 btu unit installed through the wall (high on the North wall) for about 12 years now. It does a great job for my small shop but it would be much better to use a central system in a larger shop. I have replaced the original foam filter with a 12 X 20 X 1 pleated filter that just fits between the plastic grill and the coil, but this filter is so small that I have to clean/replace it very often.

The biggest problem that you will have unsing an HVAC system in your shop is air filtration. You will need to use good high efficiency pleated paper type filters, and you will need to change them often, or your HVAC system efficiency will suffer. From what I have already learned from my system, if I was to put a central system in my shop I would put both the supply and return registers in the ceiling, or as close to the ceiling as possible too keep them out of the main flow of sawdust, and I would try to find a very large (to keep the velocity low) return register with the capability of using at least one, and possibly 2 layers of filters, or maybe even put in 2 big registers with filters to keep the return air velocity very low. By increasing the return air register size the heavier sawdust won't collect on the filter media, it should just fall off when the unit shuts down. You will still need to change the filters often if your shop gets as dusty as mine. Even with good filters, about once a year you will need to blow out the heat pump coil with compressed air. It's amazing how much dust gets around/through the filters and collects there. Keep the electric elements of any booster heat unit clean too, as accumulated sawdust can easily catch fire when these heaters turn on. Since they don't operate very often they can collect quite a bit of sawdust and then ignite it on one of those especially cold nights when you aren't in your shop. That said, I think that a heat pump is the safest way to heat and cool a wood shop.

Charley

 

[Alan in Little Washington]

Go full split HVAC- depending on the size of your shop, either one of the mini-split systems (Panasonic, Sanyo, etc.) that mount through the wall or a standard split heat pump system. My shop is insulated well enough that I seldom need heat, and never need the electric coil back-up/emergency feature, but to handle the NC summer heat and humidity, I use, and couldn't live without, the AC. If you have a contractor install it, give some thought to the filter(s). I have a great DC system but still get some airborne dust from ROS and hand sanding, etc. which quickly clogs up my standard HVAC furnace filter. I don't know how an electronic air filter would handle this dust or how often you would need to clean it, but it is something I wish I had discussed with my contractor before we shoe-horned the HVAC unit into my shop. (yes, I could have located everything in the garage, like I did with my DC blower, cyclone, and ductwork)

The air handler

The "industrial" looking ductwork:

Compressor/condenser unit:

Edit: Looks like RayH, Charles and I have the same concerns about filters!!!!

 

[brenthenze]

Thanks for all the great advice...it sounds like I should bite the bullet and just get the HVAC. Even with good insulation, the area is going to be too big for a window unit to help much. The square footage of the main shop (insulated) area is 768 s.f., but it's also an extra-tall room--I used full 10' studs--so the volume is even more than in the average 24x30 room. And I don't want to have to fill up two or three windows with separate window units.

When you talk about a "split system," that's where the air handler is not integral with the condenser, right? What's the advantage of that as opposed to an integral system?

One option that I have is that I could run the duct (and mount the air handler) above the shop, in the "loft" level, which is just going to be lumber storage (and uninsulated). If I go with ducts in the ceiling (along the sides of the building), I could have the duct run on the floor upstairs rather than running along the ceiling downstairs. Any advantages to that option, or would you recommend just running the duct in the insulated space?

Cost is a concern...I'm already a ways over budget with this project, and I'm getting to the point where I'd even consider trying to buy a used HVAC and do the duct myself. I'll almost certainly have to use "shop vac"/mobile dust control for a year or two until I can afford to get a good system.

 

[RayH]

One option that I have is that I could run the duct (and mount the air handler) above the shop, in the "loft" level, which is just going to be lumber storage (and uninsulated). If I go with ducts in the ceiling (along the sides of the building), I could have the duct run on the floor upstairs rather than running along the ceiling downstairs. Any advantages to that option, or would you recommend just running the duct in the insulated space?

IMHO that's one of the big advantages of the "split" system. You put the air handler close to where you want the conditioned air. I think the least expensive ducting is insulated tubing used in attic/crawlspace, so for short distances it's no problem being in uninsulated spaces. You will need a condensate drain line to the outside, but that's usually not a problem.

768 sq ft? Man, now I really do envy you!

Good luck,

 

[Alan in Little Washington]

As Ray said, you can use "soft" insulated ductwork if you put it in the attic- my house has soft duct in the crawl space and the attic. With a split system small copper refrigerant lines (and a low voltage control wire) run from the condenser to the air handler which has the cooling coil and fan. Both the condenser and air handler need 220V (some air handlers have 120V fans).

There is a limit to the length of the refrigerant lines, but my run 30' or more.

Non-split systems for something as big as your shop are about the same size as a "gas pack." They must have ductwork running from the unit.

As far as cost- for a shop your size maybe as high as $3-4K, maybe higher? but I am not sure.

 

[Travis Porter]

If you can afford it, I would definitely install a heat pump or gas pack unit. Prior to my current shop I had used kerosene heaters, electric heaters, etc to heat the shop when I wanted to go out. A lot of the time it took from 1/2 hr to an hr to get the edge off and at times I no longer felt like going out. It can be hard to swallow up front, but you definitely won't regret it.

I was fortunate that I found someone on the side to buy from and have them install it. They provided the refrigerant lines up front and I was able to put them in the walls before I finished them. If you do go this route, don't forget drain lines as well. I sheetrocked my ceiling first and put a cat walk in the attic so it made it easy for them to run the soft lines and install the unit. At least here I had to run two drain lines, one primary and one back up. My shop is around 800 square feet and I put a 2 ton unit with 14 seer in it and have no regrets. In the winter I turn it down to around 55 so I don't have any issues with freezing of my glues and paints.