Dust Collector- direct exaust to outdoor
twotowers
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Hi All;
I have an 1980’s vintage Harbor Freight 1 1/2 HP, single bag dust collector-Single bag units have one large bag below for collection and filtering. I believe the microns to be high and have been thinking of just building a plywood box to surround the unit and put a vent in the box arer so that all the excess dust exits the shop rather than being blown into the shop environment.
I was thinking of a 4″ by 4″ vent; does that sound logical? As it is an out building shop that probably would result in out side temperature in the bottom of the collector. Anyone see a problem with the idea?
Best
TT
Replies
We did a big thread on this a while back and their are potential down sides. Not least that the air could draw in things you do not want drawn in, like exhaust gas from a fireplace, or a hotwater heater or furnace. I would look up the old thread. It was pretty long and covered the issues pretty well I think.
PS are you a JRRTolkien fan or do you use the TwoTowers name for another reason?
Doug
One router to rule them all, one router to shape then, one router to router them all and in the Woodshop stain them. In the land of moldings where the finish lies.
Sorry could not resist. It has been a long day.
Doug et al, I remember a thread about makeup air and I don't remember it covering the topic all that well. I'm not an expert in the area, but I still have trouble believing that exhausting a hobby-size DC (1 or 1.5HP) would be a danger in most homes. I did some research a while back as I replaced my furnace and bought central vac and DC. If the DC exhausts at about 400 CFM and you fear your furnace or hot water heater, you must also fear your kitchen exhaust fan (100 to 300 CFM) or your bathroom fans (50 to 100 CMF) or your clothes dryer exhaust (150 CFM), etc. There are standards that suggest minimum house ventilation (leakage if you will) of 50 CFM for a typical 2500sqft home. That means at least that much to allow for these appliances and offer clean air to enter the house. Mine is much higher than that and I stopped looking for ways to lower it (energy savings) when I needed to research indoor air quality for my son. A tight home is not a safe one for that reason. Unless you have a very new house, it is probably much higher than the minimum already. My furnace (natural gas), as I suspect most modern ones, has its own ventilation (inlet and exhaust pipes). Wood burning appliances like furnaces and stoves might be a problem if you have a tight house which is why they should always have a CO sensor in the home. I have not directed the exhaust of my DC outside yet, but when I do, I might consider installing a reverse dryer vent with a diaphram (from outside the garage). Perhaps just installing it in the garage and running the inlet into my basement shop would be even better. That is the way most central vacs are installed and they draw 100 to 200 CFM from the house. I believe the original poster said he has a separate shop building with a wood source. If the building was not built as a residence, it probably has enough ventilation and probably only needs a CO monitor. The biggest concern should be to those in modern homes that have real fireplaces (rare now?) since that might be the appliance most affected by negative house pressure. Just a thought. :) Andy
Raising the issue of make-up air is valid, but it's hardly a make or break issue. Any shop with a spray booth most likely exhausts air directly to the exterior and one doesn't hear of many of them imploding. And spray booths exhaust far more cfm than a dust system. It's all cause and effect. Simply deal with it.
Andy;
thanks for your comments. I have electric heat - no furnace, or open flame. My thoughts were direct vent to the outside would substantially improve the air, and this would be true even if I went out an bought the best collector with a 1 micron bag. It is the small stuff that is the worst.Best
TT
Don't know about you but my DC moves a bit more then 400CFM. And even that to use your numbers is about 3 times what a kitchen exhaust will move. Also most houses have some sort of make up air near the furnace (if it is not elect) and is a newer house.
If you wish by all means go ahead and do what you want, and if it goes wrong and you live close perhaps I will be able to pick up some nice tools cheep from who ever inherits your stuff. Personally I would not do it for many of the reasons listed, first off it would make gods own mess, second it would reduce the efficiency of the system and last but not least it is a potential danger.
I know that now HVAC designer I know of would allow (and for all I know code may not allow) for a 400 CFM or greater deficiency in air supply. So if they were doing this professionally I would expect they would require a make up unit. And I would not chance it. The gain (what little their may be) is not even close to the hazard. I mean what is the benefit?
But as I said feel free to take a chance and if you are lucky you will not have an issue, but if you are not lucky you could end up in a wood box, not making thinks from wood, I would not chance it but have fun.
Oh just noticed one other point. Just because you are moving air in a pipe that is 4" dia, does not mean that a 4" dia hole will allow it to be made up, their is a bit of a large difference in pressure involved in this. Have not done the numbers but this would be noticeable.
Doug
Edited 11/24/2007 10:33 pm ET by DougMeyer
Doug, If by a 'bit more', you mean its specified at 650 CFM, then it probably pulls about 400 CFM. That is NOT alot more than a kitchen vent, not to mention running more than one of those appliances at the same time. The point I was trying to make was one of common sense instead of being alarmist. > If you wish by all means go ahead and do what you want, and if it goes wrong and you live close perhaps I will be able to pick up some nice tools cheep from who ever inherits your stuff.That's a sick remark. Is that how you normally discuss things? Perhaps I was interested in a rational thought on the subject. Maybe someone with a clue can provide some credible information. Andy
The dust collector has a one to one and one half HP motor. I haven't looked at the ratings of the kitchen or bath fan but I don't see how they could exceed one fiftieth HP. How can they pull a comparable amount of air?
> I haven't looked at the ratings of the kitchen or bath fan but I don't see how they could exceed one fiftieth HP.Well I've never done veneering and I've done very little handplaning so you don't hear me giving tutorials on their use here. Why would you comment on something you've never looked at? Kitchen/bathroom/dryer exhaust fans run in the neighbourhood of 0.3 to 1.5 amp which would likely put them around 1/50 to 1/6 HP, but that would be an extrapolation and assumes that relationship is linear. However, extrapolations from one type of system to another are obviously flawed, right? > How can they pull a comparable amount of air?Probably the biggest reason is that they operate on very little suction. Might also have to do with the open inlet and constricted outlet as opposed to the restricted inlet on a DC. In comparing electrical specs, you are looking at apples and oranges. The important point I was trying to make had to do with the amount of air moved. Andy
OK so the listed rate of a fan that sells for $50 or so (a bath fan) is expected to be close to the numbers given but we reduce the amount of a more powerful system buy 1/3? I don't understand that.
The point some are over reacting to that I was making with the so called sick comment is that we are not talking about something as simple as 'oh look my DC is not getting the dust out of my saw" if we get this wrong. We are talking about (worse case here) Oh look someone (or several someone's) DIED. This is a point that has came up more then once in the little over a year I have been here. It is something that the pros I have worked with (in the HVAC design business) take very very seriously but that some people here seam to ignore. Make the wrong assumptions here could KILL someone. Call it alarmist if you want.
We have people going on and on and on about the dangers of a Table saw. But I can not think of the last time one of these killed someone. Cut off something, yes, broke something, sure, but an eye out, yeah, but killed them, I don't remember that happening much. But pretty much every year when the furnaces kick in you get the story about someone being killed because his furnace did not vent right. Most the time this is the fault of bad maintenance but you can (and do) have other things causing the gasses to go the wrong way.
Is it likely? No, but why take the chance? What do you get for the risk you are running? Not to have to clean a bag? As I said you want to take the chance, well it is a free country, but if you do take the chance and you (like some have wanted to do) do this in the same building that you and your family live in, then all I can say is that you are nuts. The risk (however slim) is not worth what ever little advantage you may get from it.
Go talk with a pro (it will cost a few hundred to do so) and maybe he will say I am nuts and this is safe in that instance but the point is we do not know, and the gamble here is not a missing finger or an eye but in could be a life or several of them. I have had carbon Monoxide poisoning and until I was so sick I almost past out I had no idea it was happening. I was lucky and nothing happened other then a big head ache and getting sick, but these are the types of things that most people will not know about until it is to late.
So good luck and I wish you the best.
Doug
>but we reduce the amount of a more powerful system buy 1/3? I don't understand that.
You've made that obvious Doug, even though the answer has been provided. Do you realize, fwiw, that a typical window/room fan moves around 1000 CFM with only a 1/10 HP motor? I've explained why that is but I don't expect you to get why that little guy is 'so much more powerful' (clearly not) than your DC. Anyone who has been following rather than just finding bits to react to will.
> The point some are over reacting to that I was making with the so called sick comment
Grow up and discuss the issue directly if you believe you have something concrete to contribute.
> I have had carbon Monoxide poisoning and until I was so sick I almost past out I had no idea it was happening.
The little white gadget is only $50 Doug, and common sense was free, yet you chose neither. I'm not surprised you're so paranoid.
If you're concerned and want to debate/understand the issue, that's fine. That's why I brought it up. If your pros even work residential, bring them online. If you just don't like my opinion, block me out. Click on my name and then click "Ignore posts". That should solve your problem. I deal with facts and numbers. If you can't handle that and look me in the eye, stop listening and do your own thing.
Andy
Remember, if you live in a cold climate you will be exhausting heated air and you will be pulling in cold air so your heating bill will go up if the collector is used a lot.
Doug;
A huge Tolkien Fan, and have read everything I can get my hands on. Have you read him?
TT
Doug;
+++One router to rule them all, one router to shape then, one router to router them all and in the Woodshop stain them. In the land of moldings where the finish lies.
DOUG Or perhaps:Three Deltas for the wood-masters under the sky
Seven Hammers for the stone wrights on their walls of stone
Nine novices lost in plans;
One for the dark architect on his dark throne.
One plan to rule them all , one phone to find them,
one contractor to bring them all and in the contracts bind them.
In Law courts, where the shadows lieTop That!
TT
The main consideration which is always raised with an external exhaust is that you need to ensure sufficient fresh make-up air is available to your shop. If you don't , you risk drawing in exhaust from the furnace or water heater and killing yourself with CO2. The 2nd consideration is that you will be pushing a lot of heated air outside in the winter and taking in a lot of colder air, which can be a problem for your heating bill. The question of a 4" square outlet is easy to answer. The area of your DC inlet is calculated as pi times the radius squared. For a 4" inlet this is roughly 2x2x3.14 sq inches (a bit over 12). For a 5 inch inlet it is roughly 2.5x2.5x3.14 ( a bit over 18). The area of your proposed 4" square outlet is 16 sq inches.
Al;
Thanks! You raised some issues that were a surprise.
I have electric heat in free standing building and don't run the dust collector a lot. I do have the start of some breathing problems, so I think clean air wins!Thanks Al
TT
Hi again ALL. I don't really want to get to deeply involved in what looks like it is becoming an emotional topic. However, my thought when I first saw the 'kitchen fan / bathroom fan comment' was as follows: In my house the kitchen is on the first floor and the bathrooms on the 1st and 2nd floors while my shop is in the basement right beside the furnace room. If make-up air is needed for the exhaust fans (and I accept that it is) I assume that the entrance doors and normal leaks around doors and windows are a 'path of least resistance' for make-up air to the kitchen and bathrooms (as opposed to air being drawn up from the furnace room). In the case of my DC however, I would have to assume that make-up air from the furnace room is a likelier outcome.
> I don't really want to get to deeply involved in what looks like it is becoming an emotional topic.
Emotional? What, people being told they're going to die? You're overreacting. ;)
> If make-up air is needed for the exhaust fans (and I accept that it is) I assume that the entrance doors and normal leaks around doors and windows are a 'path of least resistance' for make-up air to the kitchen and bathrooms
Interesting thought but I suppose there are different factors in each case such as whether or not the basement door is closed and if the furnace is in its own closed room. In my case, the furnace does NOT draw air from the house, I have electric water, and I've disabled the wood stove. With other appliances already exhausting outdoors with airflows in the same ballpark, I can't help but think my little DC would not be a problem. Still, I've had two CO monitors for years (upstairs and down).
Those with older furnaces and water heaters (and real fireplaces) should take note, however. The DC is not the only appliance that draws an appreciable amount of air from the house. Assuming otherwise is the mistake, imo. Put your hand under the dryer exhaust outside and consider where that air is coming from.
As others, I believe this is an important topic but, as with discussions on shop wiring, I'm interested in sorting the truth from the fud (http://en.wikipedia.org/wiki/Fear%2C_uncertainty_and_doubt).
Andy
thanks for the note Andy. I realized that the topic doesn't specifically fit your situation (wish I had a separate work shop!), but when the shot was fired over my bow after my original reply I was a little concerned that that strongly worded opinion might lead someone down a dangerous path. Folks like Oneida feel strongly enough to post a warning on their machines about the dangers of external venting.
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