Will my car heat up, or cool down the garage?

Factual Questions
21

Because she can’t back out.

No calculations necessary, I lived, and worked as a mechanic in Ohio for half my life.
And I’ve seen vehicles through thermal imaging cameras.

It’s a warming effect , a very noticable warming effect on v8s and the like. At least for a couple hours

Even a small car with wheel wells packed full of snow pulled into an unheated garage will melt most snow off itself.

You have to use those heaters only because the heat of the car cannot sustain nor overcome the heat loss of a typical garage overnight.

By and large it’s a warming effect. Very little of the mass of a car is at outside temperature if it’s been driven.
Depends on how long it’s driven too.

Heat soak is a factor . A car at operating temperature doesn’t have all the heat energy a car that’s been driven an hour has.

Let’s take a manual Civic just for example , the engine plus drivetrain is 400-500lbs of steel and aluminum.
30-40 of those pounds are at 450+ f
Probably 80 or so at 280f

Cooling system is 185f 12lbs or so of let’s say water bc it’s close enough plus 10lbs rubber , plastic and copper.

Hood will average 100-110f so will everything around the engine, maybe a bit higher.

Rotors are about the same most likely.

Interior is room temp or higher.
The doors and everything surrounding the passenger area is higher than outside temp.
Wheels are too, so are tires, in fact they are probably 40-50f
So is the roof and glass.

Pretty much the trunk ,rear axle, fuel tank are close to outside temp.

Basically of a total of 2700 lbs probably 1200 is over 100f With large parts at 200-300 and some at 450+
And maybe a total of 300lbs is at outside temp
With the rest at somewhere around 40-50f.

Specifics obviously depend on how insulated the garage is.

Ive seen 7-8 degree rise in air temp an hour and 45 minutes later from pulling a Camaro in to a small garage.

22

By unheated I mean detached garage too so starting at outside temp.

Though it never fully warms the air top to bottom because you also have a several ton chunk of concrete at 40(bottom side) to a little cooler (topside) sitting under it that will win eventually

23

Yes.

Opening the garage door allows for a massive cool down.

It takes awhile for a small Rad or forced air vent to warm the space again.

The mess afterwards from ice melting off the car used to irritate my dad. But, a little mopping is a small price to pay to have a nice cozy car to use in the morning.

24

The door represents almost an entire wall that’s being removed for several minutes.

It used to take longer when people had to manually close the door. Thank goodness for modern door openers.

I’m not sure how that factors into the minimal heat loss from a cold car.

It would be an ideal mythbuster episode to find out.

25

Bad news.

26

Do you have a portable thermometer you can place in the garage to assist your test?

Just in the interest of scientific accuracy, I think you’d better stay in the garage the entire period, to avoid having heat leak into the garage when you open the door to the house to check the temp! :wink:

In my neighborhood, about half of the houses are split-levels, with bedrooms above the garages. Our master bedroom is considerably cooler than the rest of the house due to a combination of poor garage ceiling insulation, and ducting issues. Some of our neighbors will leave their garage doors open for extended periods, even in the winter. Besides the potential for theft, it often makes me wonder what the effect is on their heating bill.

27

My garage is fully insulated and has one insulated wall attached to the house. (9 foot insulated ceiling)

Parking 2 hot cars in there at -20c (-4F) outside temperature, the snow still melts off the cars and puddles on the floor. I’ll concede there’s some slat in the mix, but generally that puddle never freezes, even in the coldest (-30C) temperatures, even though it’s the lowest point in the garage, except maybe a foot or so of it nearest the door. Engines add a lot of heat to a garage (if they are warm). heat leakage from the house also contributes a lot. I rarely see garage temps 0 after being undisturbed for a long time - below about -2C (28F)

Plus, if you watch Holmes on Homes - those under-house garages’ ceilings seem to be a fairly common area of poor insulation, since insulating under floors is not as common a construction activity as regular walls or ceilings. Do you have serious heating issues in the room above the garage? I recall at least 2 shows where they open up the ceiling to find either the heating ducts are outside the house insulation, or there are significant gaps in the area above the garage door so cold air floods the ceiling airspace. If this is the case and if you have an insulated garage door, then you are heating the garage whether intentionally or not.

28

It used to be common to see a small Rad in the garage. Just enough heat to raise the temperature a few degrees.

Some builders leave a duct pipe in the ceiling to get some heat in the garage. HOH always gripes and says it’s not code. But a little heat is better than none.

29

Several minutes? Maybe one, or most likely less in a situation like this. While opening the door does let out some heat, keep in mind that the garage is pretty cold before pulling the car in, so there’s not as much of a drop as if it was room temperature. Also, something I don’t think anyone has mentioned yet, is that the car also displaces the volume of the cabin and trunk (but not the hood) when it pulls in. So it’s entirely possible that the car pushes a good fraction of the cold air that came in from opening the door right back out again.

Also why can I select any text on this website, even when typing my own reply?!?!

30

When I owned an old car, I used to talk w/ a lot of folk whop worked in their garages. Cheap heat was a common topic. ISTR hearing that even leaving an incandescent bulb on generates a significant amount of heat for minimal cost.

31

An incandescent bulb turned on is exactly the same as having a space heater of the same wattage. This applies to other types of lighting fixtures, but you have to look at how much power the lights actually use, not the wattage of the equivalent incandescent. So CFLs and LEDs don’t produce nearly as much heat. BTW, the same applies to power tools. The energy used to turn the drill bit or whatever ends up as heat.

32

Still costs way more to operate than your gas/oil/heat pump furnace or boiler. Of course if you don’t have any ductwork or radiators to tap into, then yeah. If I were serious about working on my car in a garage I would want under-slab heat.

33

My guess is that most space heaters ware higher than 60W, no? I think a bulb costs only a couple pennies a day. Which folk said was pretty cheap compared to alternatives. I’m sure there would be limits - such as during our recent “polar vortex!” :wink:

I recall some of the more “creative” sorts advocating setups where they cut the ends off of cans, fastened them together, painted them black, and fixed them to a plank facing south and leading to the garage window, using a computer blower fan.

Never tried it myself, but stuck with me all these years later as a creative kluge. :smiley:

34

Hijack - Its threads like this that keep me at the Dope. I can get frustrated as all get out about other topics in the forums, but seeing these threads reminds me why this place is awesome.

Thank you for this thread. :slight_smile:

/End Hijack

35

I don’t think that is quite accurate.
A certain amount of the electricity used is turned into visible light, which isn’t an efficient form of heating, the rest is wasted as heat. CFLs & LEDs turn more of the electricity into visible light and less as waste heat, which makes them more efficient light bulbs, but less effective in this use. Compared to an electrical space heater, nearly 100% of the electricity used is turned into heat, with very little wasted as visible light.

Here in Minnesota, we have a much more efficient way to do this: we have* ‘tank heaters’ installed on our cars. This is a electrical heater that heats just the engine itself, mainly the oil supply, and is plugged into the electric supply. Often wired to a timer or a remote switch, so you just have it come on an hour or two before you need to drive off, rather than waste energy on heating the engine all night long. (These electrical outlets will be handy when we move to all electric cars.)

*Or we used to have tank heaters. They’ve become much less common as new, computer-controlled auto engines are easier to start even in very cold weather. (Yesterday, it was -29ºF here.)

36

Opening and closing the garage door is basically negligible. Even if you do a full air exchange.

So it’s 10 outside , the 9tons of concrete that is 45 degrees exposed to the entire underside of the room does a great job of very easily making that 30 degree difference back up.
45 is convenient in this case since the below Frostline footers are making sure the concrete never gets to freezing and they keep it about 45 which is tge same as the air temp in the OPs case.

37

This is also where the you can’t add cold part comes into play.

Once you’ve done the air exchange , you now have a hot floor, relative to air temp. That heat easily gets exchanged as the heated air rises and is replaced by cold. But it takes very little of the stored heat energy of 9 tons of Earth connected concrete.

The car can heat the air further as heat causes it to rise
Making for a very inneffecient transfer of hot air to cold floor.

38

Visible light is not a waste of the heat. The power consumed by lights all gets turned into heat sooner or later. The light is absorbed by the walls and everything in the room and that becomes heat. Except for any that shines out the window, it all heats up the room. Garages usually don’t have much in the way of windows, so pretty much all of it warms the garage.

Yes, CFLs and LEDs don’t produce as much heat. They can make the same amount of light as an incandescent with much less power. So a CFL that consumes 13 watts and produces the same light as a 60 watt incandescent, will only give 13 watts of heating. But the reason is not because the power is converted to light.

39

Fuel burning heaters though produce more heat per dollar than electric heat. Sure, they cost more to operate when they are heating a whole house - but they are producing thousands of watts of heat, not just 60.

40

Uh. Yeah. This was my first thought. Your going to go from 45 degrees to 10 degrees (the outside temp) when you raise the garage door. Your gonna lose heat overall I think.