Putting Nat Gas furnace on floor, or?

54FordPanel · Jan 11, 2010

Hey All. I scored a nice used natural gas furnace on Craigslist for $100. I will be putting it in my garage. My question is, can I just put it on the floor, or is that a no-no in the garage? I wouldn't have it on while I was painting, but I know other fumes can flow around the floor and cause a possible danger.
However, if I build a platform to set it on, and raise it 18"-24", I would have it pull the fresh air from out the bottom and the floor anyway. So, would I have made any improvement? Or do I have to hang it way up high in order to not burn or combust dangerous fumes?

tigmusky · Jan 11, 2010

hang'em high. its nice to have the floor space.

It depends on what kind of work your doing. gas carb cleaner painting

Daye

rickairmedic · Jan 11, 2010

The furnace needs to be a minimum of 18" off the floor in a garage by code . Doesnt matter where you draw the air your heating from its the burners that they want to make sure are high enough up to not make you go BOOM.

Rick

54FordPanel · Jan 11, 2010

rickairmedic said:
The furnace needs to be a minimum of 18" off the floor in a garage by code . Doesnt matter where you draw the air your heating from its the burners that they want to make sure are high enough up to not make you go BOOM.

Rick

So if the burners are at least 18" up, it's ok? Hot water heaters burners are at the bottom of the tank, so I can see why they would want them up. My furnace burners are 30" from the bottom of the furnace to start with......does that count?

I have been painting in a house and smelled the fumes from the paint being burned by the hot water heater. So I was thinking if I drew the air supply from somewhere higher than the floor, and didn't pick up the heavier than air fumes, that's what I should be concerned about. Is that right or is it all about the burners?

Improved700 · Jan 12, 2010

Just installed a 75Kbtu Nat Gas house furnace in my shop over Xmas. Code in my area says burners need to be 18" off floor, but 24" recommended. I put my furnace on those cement blocks that you use to build a deck with, and a piece of plywood on top of that. Works just fine.

54FordPanel · Jan 12, 2010

I decided to go ahead and build a platform to raise it off the floor. I built a frame out of 3/4 plywood....

The furnace will sit at the front, with the air intake in the back.....

The furnace will draw from the bottom, so I built little shelves for the filters to sit on....

I finished the platform the furnace rests on with 2x4's.....

The furnace sits on top of the filters. I have a little door in the front that comes down to change out the filters....

I put a plywood "wall" on the left side, so I can use that area for storage and a 2x4 to protect my gas line and the 120v and low voltage wiring...

And right now I think the burners are 32" off the floor.
I paid $100 bucks for the furnace on Craigslist. The guy swears it works...but I had to replace the ignitor already. We'll see. I'm going to have a guy build me a plenum with several pointable elbows coming out. I need to run the gas, electrical, and the flue. 125,000 btus should heat the garage quick!

redsky49 · Jan 13, 2010

Looks good but I have a suggestion.

If your furnace is 125,000 btuh, it is likely to be around 2000 cfm supply air. As such, you will also have a need for 2,000 cfm return air. The slot at the back of your plenum stand does not appear to be large enough for 2,000 cfm. Perhaps you could add some openings around the bottom of the unit.

As a rule of thumb, a return air duct or opening is sized at a maximum of 800-1000 fpm. That would mean that you need at least 2 sq. ft. of return opening as a minimum. In the case of return air ducts or openings, you are on the backside (or suction side) of the fan, and restrictions can be more detrimental to fan performance than further downstream.

Additionally, I would not recommend wrapping the cabinet. There is nothing to gain and it will likely be flagged by an inspector.

as always, offered only as opinion

54FordPanel · Jan 13, 2010

Thanks, and I'm sure you are right. I was trying to draw my air from "above" the floor. I understood that the reason for having the burners higher up was that combustible gases hug the floor, and I didn't want to draw directly from the floor. If it doesn't really matter, I can put 3" holes all around the base to open up the air flow.

Is the code only about having the burners elevated, and it doesn't matter where the air is drawn from?

If it makes no difference where the air is drawn from, and it's only about the burners, I can change the whole thing and move it closer to the wall and lower to the floor.

As far as my little plywood wall, it's not really against the furnace, but about 1" away. Is it still a bad idea?

redsky49 · Jan 13, 2010

Sounds like a plan!

If you have forgotten the formula, a 3" dia. hole is about 7 sq. in.

I would suggest some hardware or chicken wire to keep the varmints out.

Follow the manufacturer's installation requirements, available online if you don't have a copy. :thumbup:

54FordPanel · Jan 13, 2010

Shoot, I can start over and make it wide-*** open, if it doesn't matter where the air is drawn from.

So, does anybody concern themselves with drawing air straight off the floor as far as combustible gases?
Or is it strictly about how high the burners are?

If it's only about how high the burners are, I can make it completely different.

Thanks for the input!

tdkkart · Jan 13, 2010

Personal opinion, if it matters for anything.
Since that unit is so short vertically I would have seriously considered hanging it up higher. Seems like floor space is always at a premium in shops, hanging the furnace would have free'd up some floor space.
Of course if you're garage has low ceilings hanging the furnace 4-5ft off the floor would mean that it would be a place to bang your head, in which case it's fine where it's at.

Charles (in GA) · Jan 13, 2010

The way I see it, I would want the location where the air is drawn for the burners at least 18 to 24 inches off the floor. The main blower is drawing air to be heated, but that air is not exposed to the fire. It would appear that the combustion air is drawn in at about the level of the horizontal black tube that runs across the front of the unit. I would assume that there are louvers on the front of the panel that covers this upper area, to allow the combustion air in, and to supply that forced vent air blower.

Main problem with drawing air close to the floor is dirt. The filters will clog much faster, the closer to the floor that the inlet is.

Charles

54FordPanel · Jan 13, 2010

Charles (in GA) said:
The way I see it, I would want the location where the air is drawn for the burners at least 18 to 24 inches off the floor. The main blower is drawing air to be heated, but that air is not exposed to the fire. It would appear that the combustion air is drawn in at about the level of the horizontal black tube that runs across the front of the unit. I would assume that there are louvers on the front of the panel that covers this upper area, to allow the combustion air in, and to supply that forced vent air blower.

Main problem with drawing air close to the floor is dirt. The filters will clog much faster, the closer to the floor that the inlet is.

Charles

Oh, nuts. (slaps head) D'oh! You are right, I don't know what I was thinking. Brain fart. Of course...the air I'm pulling in from the bottom is not the air I'm burning. I feel really stupid now.
Ok.......anyway.......I'll be opening that lower box way up for intake, and that will solve my problems.
Thanks everybody for the input.

Ok, how does one delete a thread that he now realizes was one big stupid question?

jvitez · Jan 13, 2010

54FordPanel said:
Ok, how does one delete a thread that he now realizes was one big stupid question?

That is precisely where the biblical parable of the log and speck come from :bounce:

No worries. I ask a bunch of sometimes dumb questions too. Dumb, until I get an answer that makes sense

Great pics. Snap a few after you've done your new install. I'd love to see it.

rickairmedic · Jan 14, 2010

Just for Laughs the huge hole you covered up on the side of the unit with the great view of the blower motor was where the return air duct mounted originally and would make a GREAT place to mount a filter rack to hold an air filter for getting fresh air into the unit to heat up

.

Rick

sillyhillbilly · Jan 14, 2010

54FordPanel said:
Shoot, I can start over and make it wide-*** open, if it doesn't matter where the air is drawn from.

So, does anybody concern themselves with drawing air straight off the floor as far as combustible gases?
Or is it strictly about how high the burners are?

If it's only about how high the burners are, I can make it completely different.

Thanks for the input!

two things
1. keeping combustible fumes away from the heat source, if your spraying laquer thinner no height will be good, in pro shopps ALL COMBUSTION AIR MUST COME FROM OUTSIDE THE WORK AREA, in your case not from the garage, if your spraying or storing flammables

2. you air intake will pick up less flamable fumes and burn them to the heat exchanger, and over time that bad all around, machine,, your lungs yadda yadda yadda

3. however as previously stated you fresh air intake must be the same square inches or more than the opening in the bottom of the furnace, I saw the old return air opening you covered, so your drawing from bottom, I am sure it has hole or knock out, that size is minimum size or every place the air has to squeeze thru, if you slot on the rear has enough squre inches your good, if not, more is needed. drawing from the bottom picks up every smell, i dont want that in my place

54FordPanel · Jan 14, 2010

Now that my brain is unlocked, I will be redoing it. That was just a mock-up. The revised version will feature 4x the air inlet.

I won't be doing any serious painting with it on. If I was using any product that puts out fumes, I would heat up the garage and then turn it off.

I did consider putting it up high, but the highest I could possibly get it would be eye level, and there's a door right there, and my head hurt just thinking about running into the corner of it.

In fact, my head hurt so much thinking about it I forgot how a furnace worked. :headscrat

redsky49 · Jan 14, 2010

Just to add to the overload of information -

Rickairmedic is correct about the casing opening. You also probably have an alternate opening on the side that is not visible. I had assumed (silly me, again!) that you were aware of that.

Many of these units are "multi-poise", being able to be mounted in several configurations; upflow, downflow, or horizontal. I can't tell, from looking at your unit, if yours is able to be mounted in several different ways, but that information would be available from the manufacturer's website. If this is the case with your unit, you may want to reconsider the placement of your unit. A horizontal location, suspended from the ceiling, might be the most space conscious for you.

Going back to the basics again:

Follow the manufacturer's recommendations regarding venting, even with a powered vent, for items such as elbows, vent length, outlet, sealing, etc. CO kills people every year.

The gas train must be in accordance with manufacturer and local requirements. Check with your Authority having Jurisdiction for confirmation of what is acceptable.

Observe minimum installation clearances, remembering that you will have future service requirements that may require such things as fan removal.

If you didn't get an installation manual, obtain one before proceeding further. The manual will have a "Test, Check and Startup" checklist which should be followed.

You should have an emergency shut-down switch located next to the exit from the garage. Provide a red face plate for the switch and label "Emergency furnace shut-off".

It doesn't appear that you will require a condensate drain but confirm that prior to installation.

In another thread, someone had asked about drip legs for gas piping. Technically these are dirt legs and should extend 6" below the tee fitting at the unit.

Post pics as you proceed and we will help to keep you on the straight and narrow path.

As always, offered only as opinion

54FordPanel · Jan 14, 2010

rickairmedic said:
Just for Laughs the huge hole you covered up on the side of the unit with the great view of the blower motor was where the return air duct mounted originally and would make a GREAT place to mount a filter rack to hold an air filter for getting fresh air into the unit to heat up .
Rick

If I'm drawing from the bottom, I wouldn't need the side open, would I? The bottom opening was 2'x2'.
I could cut out that side plywood, and mount another filter there if it would be better, but isn't 4 sq' on the bottom enough? That's as big as the outlet.

rickairmedic · Jan 14, 2010

54 My thoughts were if you opened the side back up and drew your air from there you wouldnt be drawing in dirty air off the floor and that opening was plenty big enough to feed the furnace before so you could leave your base alone just as it is .

Rick

54FordPanel · Jan 14, 2010

Ok, I understand. I will be re-doing it, but I think I will still use the filters off the bottom. and I will post pics when I get it hooked up. Thanks, everybody.

54FordPanel · Jan 16, 2010

Ok, Part Deux. I drilled 22 holes, 3 1/2 inches, to open up the air flow. I hooked up some 120v with a switch, I dropped my gas line down, and I put up an exhaust duct to the previous exhaust ducting. Put on a cheap thermostat, and..vola! Heated garage!

I had to move the gas line from the right to the left.....and other little things.

I know I guy that can build me a plenum, and I can plumb off of that for heat ducting.
I want to figure out how to slow the fans down a little bit. I know it's a matter of switching some wires.

Thanks everybody for your input.

rickairmedic · Jan 16, 2010

54 there should be a set of wires comming from the blower motor to the control board should be Black = High Blue = Medium and Red = Low . The board should be marked where these wires hook up should be one spot marked cool and one marked heat and up to 2 spots marked park. You want the Red wire on Heat as that is the lowest fan speed setting .I wont swear to it but I think the wires in question are on the left side of the board as your facing the unit in your first picture .

Rick

54FordPanel · Jan 16, 2010

Thanks, Rick.
Looking at the board, it says Black=High, Blue=Med High, Yellow=Med Low, and Red=Low.
And looking at the chart on the furnace, it seems with the 125K btu furnace, they recommend a Blue=Med high fan speed. Does that sound right? Right now, the Yellow=Med Low wire is wired to heat.
Should I move it to Red=Low? Or should I leave it alone? I was told the slower speed would be better for getting hotter air out....is that right? I hold my hand over the output and it seems that there are cold jets of air mixed in with the warm ones.

rickairmedic · Jan 16, 2010

54 I think putting a plenum ontop of the unit will help alot in your air mixing but give the Red=Low a shot and see what you think for now till you can get a plenum put together. The only adverse effect the Low speed may have if any would be cycling the burners more often as the high limit kicks them off more often to cool the heat exchanger.

Rick

54FordPanel · Jan 17, 2010

Ok, gotcha. Probably putting a little back pressure on it helps, huh? I'll wait until I have the plenum on, and then experiment.

Thanks.

Kevin54 · Jan 17, 2010

For a more aesthetic look to it, you could have cut 4 rectangular holes and mounted register grates in it. If you may the holes snug enough you could put silter material in the grates / grilles. This would also keep critters out and dirt from getting in. Pulling the air off of the floor is going to drag in a lot of dust. You know how dusty garages get anyways. I would have also mounted it up a little higher but you could still have left the box to the floor. Could you mount it up 2-3' high at the bottom? If so, then you could pull air in from a lot higher area and eliminate a lot of dirt going into it. It would also keep you from going to your knees to change out the filter.
One thing to also remember is that some fumes and gas can creep across the floor, so drawing air from up higher is a little added insurance.

cghsparky · Jan 18, 2010

Might also change that flex gas line going through the furnace cabinet to black pipe,after time they can rub a hole in the flex line.

cghsparky · Jan 18, 2010

After looking around i found a old pic of my furnace with the return air elbow and filter rack.

Putting Nat Gas furnace on floor, or?

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