A garage thermodynamics question.

 So my garage is notoriously cold in the winter and, where I live, it is very cold. But, in my garage, I have the panel in the ceiling that leads to the attic, which is historically very hot. So, check my understanding of the laws of thermodynamics. Could I leave the attic access panel off, and that would cause the warm air to migrate toward The cold air down below, even though we know that hot air rises and cold air sinks? Or, would this just cause the warm air of the garage to go up, and the cold air of the attic to go down making the situations even worse?

well, if the bottom of the attic is warmer than the top of the garage, then not much air will move (unless you force it with a fan). If the bottom of the attic is colder than the top of the garage, yes, it will fall into the garage displacing the warmer air at the top of the garage into the attic.

as always, I don't know anything about anything, but I'd say if you opened a porthole into the attic you would lose any thermal layer you had going on in the garage.

your best bet is to move your garage items into the attic and move the hot air down into the garage where it will heat the floor from below.

Is your garage attached to the house? More importantly, is the attic over the garage shared with the rest of the house?

If it the attic is vented, which it should be, in the winter time it should be pretty close to ambient. If you leave the panel off in the winter and the garage space is warmer than the attic, then it will cause a bit of stack effect and probably pull the heat up faster. The kicker is then infiltration has to keep up with the draw of the stack effect and you have cold air coming in around windows/doors/sill plate.

In reply to STM317 :

Yes to both. 

Kinda looks like I’ll need to get a couple remote thermometers and place them on the ceiling of the garage, and then floor and ceiling of the attic. Test accordingly. 

I know hot air always moves toward cold, but I also know hot air rises and cold sinks. But which law takes dominance?

_ said:

I know hot air always moves toward cold, but I also know hot air rises and cold sinks. But which law takes dominance?

the second is the only 'law'. The first is logically contrary to the second.

 

I know hot air always moves toward cold, but I also know hot air rises and cold sinks. But which law takes dominance?

Hot air does not move towards cold... Hot air is less dense than cold air, which is why relatively colder air hangs around low spots and relatively hotter air hangs around high spots. It's also why your car makes less power when it's hot.

If your goal is to make your garage warmer, get a heater. Cutting a hole in your ceiling can only make it cooler.

Agreed.

Any heater you get will be dramatically improved with the use of a fan.  The only caveat is with radiant heaters which don't heat the air, they heat surfaces.  But even then, the hot surfaces convect heat to the air, it rises, and then a fan would help.

The radiant heater in my shop at work does wonders, but I still have a fan blowing down as there is a pretty good thermocline at about 10' up.

Cutting a hole will only remove an extra layer of insulation and allow cool air to pour in from the attic and allow the air you've heated to escape up.  Less shared air space means less need for heat energy.

If the sun shining on the roof shingles all day is heating the attic space, and the cold ground is cooling the garage space, then a fan and duct system might eliminate the need for a heater.  You could blow the hot air down to a vent at the floor of the garage, aimed across the floor.  Then add a vent in the roof on the opposite side back into the attic.  You could set up a cycle where hot air is forced down, then blow across, then rises back up. Once the circulation is established, the fan would not even have to work hard.  This is of course based on a complete an utter lack of understanding of the laws of thermodynamics, but Red Green would approve.  

The hot air rising will radically trump the heat flow from warm to cold.

The first is convection involving actual movement of air molecules.  The second is only the radiant energy transferred from molecule to molecule.

You need to be looking at why your attic is getting so  hot. 

If the ceiling is properly insulated the heat from the living space would not be heating the attic a lot. 

I don't live in snow country but have read that a roof that won't hold snow because it melts off of it is a sign that the attic is getting heated from a poorly insulated ceiling above the living space. 

I have a mr. heater. The propane is headache, literally. The fumes suck. The only way to reduce fumes is opening a garage door, which defeats the heating. The attic is always “warm”. Not abnormally hot. In comparison to the garage cold. That’s why I think a blower to the garage floor would be best, with a return to the attic. 

I think a couple of radiators with box fans attached, some tubing, and a plug in water pump could make you a quick heating loop to steal that heat from your attic and put it in your garage.

In reply to MrJoshua :

Water in the attic... not a fan. Lol. 

_ said:

In reply to MrJoshua :

Water in the attic... not a fan. Lol. 

I think it would work better with the fan.