jharris

Hello all,

I recently purchased a two burner forced air unit for my shop. It is barely used and because it was offered for only $150 I bought it.

Only after I got it home did I consider the safety of installing it in dusty wood shop.

The combustible air will be from the shop and have a standard furnace filter. I'm thinking that I will use cleanable and reusable filters to maintain the efficiency of the unit.

My main concern however is the possibility of the unit kicking on when the air in the shop contains just enough dust to ignite and blow me up (fuel, oxygen, flame, BOOM!)

Any thoughts on this?

Jeff

yocalif

How did woodworkers heat their shops a 150 years ago? Thats right they burned their scraps in a wood burning stove.

Use your head and some common sense, you will figure out a way to make it work.

joesbucketorust

150 years ago they'd be creating more shavings than dust in a small shop. A factory might be producing a lot of dust, but then they wouldn't be using a wood-stove to heat a factory, they'd most likely be using a big steam boiler and piping in hot water to the radiators. Those boilers would sit in another room, or in some of the bigger factories they would take up their own building.

I'm not saying the heater is safe, or not safe, just saying that the comparison to a wood stove 150 years ago is a bit apples-oranges.

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jharris

Thanks for your input but not much help.
I guess I should have started this thread by asking if anyone else heated their shop in this manner and would be willing to advise me on my safety concerns.

This is not an issue that I care to resolve by trial and error.

Jeff

TomC

I no expert on this by any matter. However, I don' t believe you will have a problem. I use an open flam propane heater with a blower. It looks like a torpedo kerosene heater. I start it and the jet air filtration unit on to mix the air up in the shop. I have never had a problem.
Tom

Gene Howe

Not sure how it might compare, but I use a Pro Com heater Pro Com with an exposed flame on start. It's also ventless. I've had no problems at all. However, it's maybe 20 ft. away from the sanding table and I have decent
dc capability. I realize that 20 ft isn't much and that dust does linger in the air.
A concern for you might be the return air. Any way to build a box for filters, similar to a home made air cleaner, and attach it over the return air vent? Or any way to put the furnace in another area and duct the heat into the shop?
Could an air cleaner be in your future?

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Gene

'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

joesbucketorust

If this is a portable unit that plugs into one of those little BBQ style LP tanks, please shoot me a PM with the details (model, where to buy etc.) (don't want to hijack a thread.) I only need a heater for a month or so each year and that sounds like it would heat the shop up faster than the electric space heater.

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TomC

Joe, I just PM you. I had left out a letter in you address or name.
Tom

troyd1976

i have one of these propane hook up types you can get at Menard's,i have it mounted to the wall, but i believe you can also get pedestals. they also make little blowers you can put in them, but from what Ive read thats a waste of money, i just use my grizzly air cleaner to circulate air. normally i use it for quick warm up, than if i need to keep warmth in there over night for drying i run an electric portable radiator. for my application, an insulated 14x20 garage, the propane heater tends to be overkill if left run for hours on end even on low setting. i believe they are sized actually for a 2 car garage.

TomC

You are correct that you can't leave the propane heater on for hours or it will drive you out of the shop. I usually get the shop in the low 60's and then turn the heater off. There is no way I would leave it running over night; even on the lowest setting for safety reason alone.
Tom

jharris

Tim and Gene,

Thank for your input. I have considered an air filtration unit. I need one anyway. The purchase is justified for respiratory health reasons and now with this shop safety consideration I should probably evaluate this option.

Because the heater will be installed on an exterior wall I have the option of attaching a heater shed to the exterior of my garage wall, however as busy as I am I don't want to tackle that right now and I think if I'm using cold exterior air for combustion I'll lose some efficiency yes?

At this point I will search this site for info on filtration system posts.

Incidentally, I'm taking steps to control dust at the source. I have dust chutes ordered for my DW 734 planer and Delta bench top jointer.

I also used a step adapter,cut in half to enable connection to both my hand belt sander and my table saw to my Sears two stage dust collector (need a better one but cost and floor area expenditure are the snag).

The answers to my questions are really beginning to gel thanks to your input.

Any further input will be appreciated. Keep ya posted on my progress.

Thanks.

Jeff

PSDkevin

I use one of those torpedo/bbq things. Works pretty good.

I am certainly no expert. I dont know what the ratio of dust to air required for ignition but I believe you would have to have seriously high levels of dust. You cant ignore the dust but I think as long as you are capturing most of the dust at the source and have a basic filtration unit you will be okay. Never an issue with mine.
I am much more worried about flamable vapors from finishes etc. Oh and carbon monoxide. Gotta have some air exchange if you are heating with combustion. So I crack the garage door and let the heater suck in the air from outside.

One problem I also get with the little propane heater is that if I rapidly heat the shop I get condensation on my cast iron. Also try to keep about 3 feet clear around the flame. Nothing combustible.

Domer

I have an electric 220 volt heater in my garage with a rough thermostat. I checked with one of my friends with HVAC experience. He told me that the biggest threat is build up of saw dust inside the heater and to regularly clean it out inside and out.

I do not have an air filter but to have a dust collector that I use pretty religiously and I do clean up pretty often. Also all of my sanders are connected to my shop vac which has a really fine filter so I do not have a lot of air born dust.

The air born dust is a real hazard both from a fire standpoint and health risk as well. So if you create a lot of air born dust, I would definitely invest in an air filter as well as dust collection. I would check out how well the air filter works before I put in the heater.

My heater does not have a filter at all and does have a blower. I clean it out once a month or so. It only takes a few minutes.

So I feel pretty safe with it.

My 2 cents worth

Domer

rrich

Jeff,
Don't worry about the dust / explosion thing. You wouldn't be able to breathe if there was enough dust in the air to support combustion. There are other concerns.

A gas fired forced air unit has two air paths or uses.

The first is the air that supports the combustion of the gas. The gas that results from combustion needs to be exhausted from any habitable space. It is best that the air to support combustion is drawn from outside the dwelling but not absolutely. If the exhaust is allowed back into the habitable space, eventually the oxygen in the air is depleted and incomplete combustion occurs yielding Carbon Monoxide.

The second is the air from inside the dwelling that is warmed and forced from the unit and back into the dwelling.

My suggesting is to build a closet for the forced air unit keeping the two air paths separate.

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Rich (Tilting right)
Huntington Beach, California
Remember that when we have the "BIG ONE" everything east of the Rockies falls into the ocean.

Firewalker

I will tell you what I have been using for 10 years or so. I have a deerborne heater that was set up for natural gas. I pulled the orifice and connected it to a bbq grill propane bottle. With the orifice out it will really put out some crazy flames but I use the reg to make it as high as you would see one burning in grandma's house.

Until recently I have never had a DC or a filtration system. I have done a fair amount of sanding and have never had ANY trouble whatsoever. I am now running a wood stove and I don't anticipate any problems with that either.

I am not saying you shouldn't be concerned but it sounds like you are in a lot better shape than me if you are using a DC with appropriate gates and filtering the air.

My $.02 Good luck to you.

Scott

TomC

not sure I understand this. The hotter the air the more moisture it can hold. I know when you burn natural gas you get some moisture. I assume you would also get it with propane. However, heating up slow or fast should put about the same amount of moisture in the air.
Tom

PSDkevin

Good question. When heating faster im burning more and putting more moisture into the air faster. Long explanation short... it takes some time for that frozen cast iron to heat up so... viola...condensation. when i heat slower the air exchange keeps the moisture lower..well at least low enough and for long enough for the cast iron to warm enough...you get the picture

TomC

No, I don't think I do!

firehawkmph

Jeff,
I use these direct vent forced air furnaces by Williams. Have three of them now in three separate areas, garage and two shops. They are quiet, pretty efficient, and most of all, safe. They have a sealed combustion chamber and draw intake air from the outside. They are fairly easy to install and not too costly to run. I can heat up my 26' x 28' shop in the dead of winter in about 15 minutes. After it reaches temperature, it cycles on about once every 15-20 minutes, depending on how cold it is outside. Current cost is about $1200.
Mike Hawkins

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PSDkevin

I am not trying to be a smarta$$ here. Nor was it my intention to offend. I was simply trying to be brief in my explanation. I say that because I can take this quote two different ways. I will assume you mean no offense here either...

This further clarification is intended in good spirit and to help the OP as well:

I was simply saying in my original comment to the OP that I have problems with condensation on my cast iron when I use my little propane heater. I'm not Bill Nye or anything so what I think is happening here is what I described. As you said burning propane does in fact produce moisture. So when the heater is on high you are burning more propane. More propane=more moisture. My garage is completly uninsulated and unheated (when I'm not running the little propane heater). When I run the heater on low at first (and I keep the garage door cracked as I said in my original comment) I am putting less moisture in the air because of less propane being burnt and the opening in the garage door allows the cooler/dryer air to mix with the warmer moister air. (not trying to be smart here either. Just for those who want to understand)Condensation occurs when water vapor comes in contact with a surface that is cooler than the dew point tempreture. When the heater is on low it can warm the air to the point where the cast iron can start to warm. In my case I am able to warm the cast iron surface above the dew point tempreture before the humidity rises high enough. I cannot do this when the heater is on high. For those trying to make a decision on how to heat their shop this is something they should consider.

Sorry for the being long-winded