# Vent or Heater

My husband seems to think that the car heats up in the cab just as fast by having the heater set on low. I have proven time and again that setting the vent on high (after the car has idled for a minute or so to warm up) heats up the cab faster. Can you please tell us who is right?

Is it worth really arguing over? Probably both, perception is key.

Well, perception about what’s worth arguing about too. I go with Mrs. Heater is just another radiator cooling
the engine. Faster to fan - cooler the radiator (heater core) - warmer the cab.

The faster the fan, the more heat is extracted from the heater core into the flowing air. The faster the fan, the cooler the air will be. The faster the fan, the faster you drive already heated air out of the cab. There is an optimal speed. It probably depends on the temperature differential between the cab and outdoors and what the coolant temperature is.

What you need to do is get a couple of thermometers to measure cab temp and outdoor temp. You also need to install a relatively precise coolant temp gauge. It would be best to use a circulating heater to pump coolant through the heater core at a fixed temp after unhooking it from the engine while you are making observations. Start to make observations varying the fan speed. Make a big table. If you keep at it, you might have enough data by the end of this winter. Let me know when you are ready to present it.

Here is another possible solution. Heat transfer engineering specialists make calculations like this all the time. Maybe you can find one and borrow some computer time.

I vote with you.

The engine warms up at almost exactly the same rate regardless of the speed of the heater fan. However, with the fan turning faster it’s drawing more heat out of the heater core and pushing it into the cabin.

But, there is a perception issue as noted. Until the air hits 98.6 degrees, in adition to drawing heat from the heater core and sending it into the cabin it’s also cooling your body parts. So, if the outside air is 20 degrees, and the engine is still warming up and the air coming out the heater is 50 degrees, the air blowing out the heater will be cooling your body…and the faster it blows, the cooler it will feel. If he’s wearing low sneakers and you’re wearing high boots, you may be okay and he may be freezing his ankles off.