Venting DC Outside?

[Greg Funk]

Greg, Be sure to wear a respirator when you go outside! That is amazing to hear, but you don't know till you test.

No, I think I'll just cut down all the trees in our neighborhood...

[David Giles]

Outside dust venting has some obvious advantages, but some disadvantages. The dust may blow away to nearby fields, but chip collection is still an issue. Try to avoid hauling those chips out of the basement if you can.

Outside venting works best with big, open, drafty shops in a warm climate. I'd second the cartridge filter idea.

[Greg Pettis]

Last fall I vented my dust collector outside. The DC is a Delta 50-850, a 1.5 HP system which, if I remember correctly is an 1100 CFM unit. The DC motor & fan assembly is mounted near the ceiling on an outside wall. The ducting from the DC is 6" PVC with only the drops reduced to 4" to connect the various machines. The unit discharges through the wall via another 6" PVC pipe and is currently dumping on the ground. I will be building a box of some type this spring to contain the chips.

My shop is 24 by 30 with 8+ foot ceilings. The heat source is a 45000 BTU vented propane ceiling mounted unit. There is no makeup air provision in the shop. The shop is located about 200 miles north of Minneapolis, Minnesota where it does get cold.

Observations:
- Without the resistance of the bags, the airflow through the system is much improved resulting in a higher degree of chip collection with very little dust escaping. Until venting outside, I was seriously considering upgrading the DC as chip collection was just OK and even with oversized 1 micron bags, there was always dust everywhere.
- In December, I planed about 200 board feet of aspen, jointed it, ripped to width and then used the router table for tongue and groove on the boards. Essentially, for two days, the DC was running for the majority of the day. Outside temps were around 20 degrees, the thermostat was set for 60 in the shop. The cycling of the heater did not seem materially different than when the DC is not running. Had essentially the same experience in January with similar temps and an extended amount of DC run time. A 25 mph northwest wind has more impact on how much the heater runs than the DC seems to.

My less than scientific conclusions are that makeup air is not needed; heat lost through the DC is minimal; and most importantly, a DC which was marginally adequate gets a huge performance gain by venting outside. This all seems contrary to the calcualations and scientific theory but, I am making sawdust without getting any on me and I'm staying warm.

In your basement shop setting, the comments about providing combustion air for the furnace should be taken seriously. Installing a carbon monoxide alarm near the furnace (don't forget a gas waterheater or any other gas fired appliances in the basement) is a basic safety measure as it takes very little to disrupt exhaust gas flow.

Now you know everything I know...

[Dave MacArthur]

Edward Warren-- I'm thinking of doing the same thing as you, interested in the replies. Greg Pettis' post above seems very pertinent.

I live in Phoenix, and so air re-circ is not needed. My DC, a Delta 50-760 1.5 HP with 1 micron bag, seems quiet to me. I was thinking of putting the thing up in my attic above my 3-car garage shop (1 bay mine...), with the chip bag below in the shop, and just exhaust via a vent out the top of the roof two stories up. I'd think a very oversized run from the DC (8"? ), longish run, would make the exhaust up high not even as loud as people's air conditioners; and any small dust should be un-noticeable up there. Inputs?

[Edward Warren]

Exactly what I was thinking. For me - I would save some $$$ and not get a cartridge filter...I'd just build the chimney instead with an 8" or larger duct. This way I wouldn't have to deal with servicing/cleaning the top filter.

[Phil Thien]

you need to be very careful when exhausting [a dust collector] outside if you have a gas furnace.

I've read this advice several times, and I've also read reports from those (with gas furnaces) that are ducting outside w/o any problems, and I wonder...

Is there perhaps a difference if one uses a newer, super high-efficiency furnace? Those that vent vertically out a PVC pipe, to the side of the house? I imagine those exhaust under pressure, whereas my older (less efficient) furnace relies on the lighter exhaust gasses to rise through the chimney (under no pressure), and the negative pressure created by a DC exhausting shop air would be more likely to pull those deadly gasses back into my shop.

I'm just worried that the anecdotal evidence ("it works for me") may lead someone to try it and have the opposite (and possible deadly) result.

Of course, maybe some of you are using older furnaces like mine. Just thought I'd ask those of you already exhausting outside what kind of furnace exhaust you have.

[Keith Outten]

I have been using an outside chip box for over 15 years in my shop. I originally did the math to calculate the cubic feet per minute of air removal....although it seems very scientific it doesn't apply because the heat loss is minimal in actuality. Most of the heat in a room is in the furnishings, in this case your tools, floor, walls and equipment. My setup doesn't use any filters or return air system.

I live in Virginia, our winters are not as cold as in the northern areas of America but we do experience some very nasty cold snaps that can bring the temps into the teens and occasionally single digits. Over 15 years I have not experienced a problem based on outside temperatures.

I have installed the same system at Christopher Newport University that I have in my shop at home. In fact I have two dust collectors at CNU, one for the ShopBot CNC Router in the shop area and one for the Laser Engraver in my office. The shop DC dumps directly to a box outside. The DC in my office feeds to a standard wall vent, the same as you would use on a clothes dryer. There are no chips associated with running the laser engraver so there is no need for a cip box.

I often run both system at the same time with the router running long periods cutting full sheets of material all day long. At the same time I am in my office running the laser engraver engraving plaques all day long. The system at CNu has been working for over a year now without any issues.

Note that both my personal workshop and my shop at CNU both are heated with heat pumps so I don't have the carbon dioxide issue to be concerned with.

Here is the bottom line.........I am not breathing the junk in the air when it is pumped outside. If there is a little bit of heat loss I can easily justify the cost.

I can purchase the cheapest dust collection equipment and experience the same performance as the most expensive units because all of the resistance has been eliminated. This has been working well for me for over 15 years but I won't claim that it will work for you but it is worth the time to experiment with your own system in order to breathe clean air even when a 3.25 HP Porter Cable Router is cutting MDF for hours and hours every day without leaving any fine dust anywhere in the shop.

Greg, it looks like its just you and me

.

[David Giles]

Let's make it the "three dustateers". Bad pun. Keith, count me in as a big proponent of outside venting. Chris, can you install a big drop box outside of house? Or can you just let the chips pile up on the ground? Resolving the chip handling issue has been the hardest and least satisfactory part of my outside DC venting experiment.

Without a drop box, Chris would locate the chip bag inside the basement or outside the window. I'm visualizing him changing a full bag in full darkness during a blizzard after digging his way through snowdrifts. If you have to locate the chip bag inside, would you still recommend outside venting or just go the more conventional canister route?

Totally agree with your heat loss position. Most of the heat is in the floor, walls and tools. A small wood stove or other radiant heater should keep the work area warm even with cold outside air coming in. The air just cycles out pretty quickly. I use a halogen lamp to keep warm. Not that us Houston boys know anything about cold!

[Matt Meiser]

Is there perhaps a difference if one uses a newer, super high-efficiency furnace? Those that vent vertically out a PVC pipe, to the side of the house? I imagine those exhaust under pressure, whereas my older (less efficient) furnace relies on the lighter exhaust gasses to rise through the chimney (under no pressure), and the negative pressure created by a DC exhausting shop air would be more likely to pull those deadly gasses back into my shop.

That's my assumption. I know that the furnaces that are power-vented have a pressure switch in the flue that shut them down if there isn't a proper draft. My shop furnace is power vented an it has never shut down, nor has my CO detector gone off.

Before I comitted to this route, I tested for several weeks by cutting piece of plywood to fit a window near my cyclone. I cut a hole in the board for the exhaust and used some foam weatherstripping to seal it up as best I could. There were no issues so I proceeded to cut a hole in the wall and install a permanent vent. I wouldn't even try this without a CO detector.

[JohnT Fitzgerald]

many of the newer high-efficiency furnaces also have piped-in fresh air.

[Jim O'Dell]

many of the newer high-efficiency furnaces also have piped-in fresh air.

Phil, some of the newer furnaces are sealed combustion units. That's what I was talking about in the last line of my post. I'd still be careful with that type of system, but if everything is working properly, then it's not as critical as a unit that gets it's combustion air from the house.
Jim.

[Andrew Duncan]

Thanks mostly to previous posts by Keith Outten, I, too, am an outsider. I threw away the filters and bags and extended the exhaust line about 10 feet through the shop wall. Periodically I rake the chips around the area they pile behind the shop in the woods. I do live in the country, so there are no issues with neighbors.

Like the other outsiders have noted, DC performance improves DRAMATICALLY without the filters and bags and I also have noted no change in heating issues in the shop since I completed the change over.

I posted a thank you note to Keith along with more details on my dust collection conversion some weeks ago. This is a great DC improvement for anyone who can find a way to do it.

[Chris Jenkins]

Thanks for all the input. I didn't even think of drawing CO from the furnace. I built a room around the furnace to keep it relatively dust free, but I didn't seal it air tight as it needs fresh air coming in. If Air can come in then CO can come out.

I initially only wanted to do this to keep my air a bit cleaner. But from one of the posts it sounds like I can keep my cleaner with a good filter, which I have a canister filter now as it is. I run 6" ducting and 1 5" drop.

I was initially thinking this would only be a "Summer / Fall" thing for me, which is why I asked the original question pertaining to the cold.

I'd love to test something like this, but I don't plan on cutting a hole in my house and trimming out the siding just for something I'm not even sure of.

I think I will just go with the Phil Thein Baffile until I get a cyclone in place.

I'm going to keep researching, but no holes in the side of the house as of yet.

[John Newell]

Not all of us are living in homes heated with the latest/greatest...so...

My less than scientific conclusions are that makeup air is not needed;

Taken at face value, that's just wrong. What I think is meant is that special provisions for make-up air may not be needed?

We live in a fairly leaky 1964 colonial in Massachusetts. Heat is oil-fired hot water boiler with a "blower"-type oil burner. Until we removed it a few years ago, the whole-house fan between the attic and second floor was capable of snuffing the oil burner if the windows and doors were shut.

I'm pretty sure that the CFM that fan was moving is greater than a 1.5hp DC, but folks need to be very careful. Even without the obvious clue of a burner being extinguished, you could definitely be sucking CO and other combustion gases into the house. I have been considering a direct outside exhaust DC setup, but when we're doing this, caution is warranted, I think.

[Ken Ganshirt]

John,

You've raised an excellent point. Greg did not give us any information about how tight his shop is. If I tried to vent that 1.5HP dust collector out of my shop without cracking a door for makeup air, my shop would implode. I built it for Canadian winters and it's Tight, with a capital T. There aren't any significant areas of air infiltration for the necessary makeup air.

Greg,

You absolutely DO need makeup air. You can't shove 1100 cubic feet of air out of your shop every minute without your shop turning into a vacuum chamber unless there's 1100 cubic feet of makeup air coming back in every minute. In your case you must have a leaky enough shop that a satisfactory amount is coming in through the leaks.

I'm one of those who was considering exhausting outside instead of dealing with the issue of how to effectively filter my dust collector as it recirculates the inside air. I even have a spreadsheet that allows you to calculate the cost for electric heating if you vent outside. Once I got my Dylos particle counter (0.5/5 micron)I changed my mind.

I have a 1HP King dust collector with a 1 micron upper bag and plastic lower bag. If I run it for two hours I can pull the fine particle count from a reading of 14,000 down to a reading of 20. That's with a filter bag that has a pretty good cake on it. If a person was using a cyclone with a 0.5 micron pleated filter on the return air, they would be easily able to filter their shop air as well or better than any air filter on the market.

What persuaded me not to bother with the option of exhausting outside was that I have taken a few outside readings. Like someone earlier in this thread, I discovered I can get my shop air at least an order or two of magnitude cleaner than my outside air just with a well-caked filter bag and an underpowered dust collector (not a combination I'm recommending! simply what I had available to measure).

...ken...