How to estimate the BTU/h for automotive radiators with fan?

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monteville

Feeling the Heat
Nov 23, 2019
435
Dallas
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Automotive radiator is an affordable and available alternative to hot water room heating radiators. It is also lightweight, enabling women, elders and the physically challenged to carry and install. They have matching fan and shroud to blow air through.

How to estimate the BTU/h for a certain automotive radiator for 75F ambient air and a certain CFM of the fan?

I know they are not rated for the maximum power of car. Can we use car's highway MPG as a ball park estimate?

For example, assume highway speed is 60mph, a 30mpg car use 2 gallons of gasoline per hour, or 230K BTU per hour. If engine has 10% thermal power carried away by coolant, it's 23K btu/h through the radiator with coolant temperature 195F, so we can use this radiator instead of a 23K heating BTU PTAC unit.

However, the above have not considered the 60mph airflow while car is going 60mph. Radiator fans typically only blow air by 5mph. How much BTUs should be discounted from the air speed difference?

so let's further estimate the numbers:
Radiator size = 400 square inch, at 60mph there is 2.14 million mol of air passing through it per hour, air's thermal capacity is 30J/mol*K, put 23K BTU in, in this condition, temperature rise of air is 0.37K.

If we blow it 5mph instead, the temperature rise will be 0.37*(60/5) = 4.44K, right? Seems not a significant rise of outlet temperature, or thermal conduct rate. Point out my mistake if I am wrong.
 
Last edited:

E Yoder

Minister of Fire
Jan 27, 2017
598
Floyd, VA
Sounds like a complete shot in the dark. Normal unit heaters are pretty low cost, I'd use a rad with a known output and with copper tubing (v. aluminum). ?
 

SpaceBus

Minister of Fire
Nov 18, 2018
7,047
Downeast Maine
I think any automotive radiator and fan setup would be too big for most home heating applications.
 
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monteville

Feeling the Heat
Nov 23, 2019
435
Dallas
I think any automotive radiator and fan setup would be too big for most home heating applications.
yes, too large for room heating, what about in duct plenum that heats the whole house / building? What about heating a commercial building's hallway?
 

SpaceBus

Minister of Fire
Nov 18, 2018
7,047
Downeast Maine
yes, too large for room heating, what about in duct plenum that heats the whole house / building? What about heating a commercial building's hallway?
Sure, it's probably close to commercial heating needs, but even still, I think most people like to use UL tested/approved components in the event of a failure.
 

salecker

Minister of Fire
Aug 22, 2010
1,836
Northern Canada
Unless you live in the middle of nowhere...
And have the ability to do your own work...
Why look for alternatives to proven components?Especially for your home.
I thought of making a basically free greenhouse heater out of used tires on rims and a bunch of garden hose and an old rad.Free except for my time.
 
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monteville

Feeling the Heat
Nov 23, 2019
435
Dallas
Unless you live in the middle of nowhere...
And have the ability to do your own work...
Why look for alternatives to proven components?Especially for your home.
I thought of making a basically free greenhouse heater out of used tires on rims and a bunch of garden hose and an old rad.Free except for my time.
I think automotive radiators, especially for popular cars, are proven far more in real world use than HVAC radiators. They have far more hot/cold cycles than HVAC radiators, frrom near boiling to freezing cold, and we see very few of them crack without collision.
 

SpaceBus

Minister of Fire
Nov 18, 2018
7,047
Downeast Maine
I think automotive radiators, especially for popular cars, are proven far more in real world use than HVAC radiators. They have far more hot/cold cycles than HVAC radiators, frrom near boiling to freezing cold, and we see very few of them crack without collision.
I have had a spontaneous radiator failure in my life, but generally speaking they are rare. I have never heard of a home heating heat exchanger spontaneously fail, ever, so even more rare. Aside from getting a setup from a junkyard, I don't see the advantage of using an automotive radiator. Getting the plumbing to mate up will also be frustrating. Automotive systems run at lower pressures than my home plumbing as well.
 
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E Yoder

Minister of Fire
Jan 27, 2017
598
Floyd, VA
Hot water coils have been used by the 10's of thousands so I don't think I'd rig up a car radiator. I would guess the car rad would be aluminum which brings another metal into the system. And the piping wouldn't be 1" copper like a standard coil.
A regular copper tube coil is available in many many sizes all over the internet. Search for outdoor boiler coil or water to air heat exchanger.
 
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woodsmaster

Minister of Fire
Jan 25, 2010
2,885
N.W. Ohio
I’d check the pressure rating, don’t think the are made for the max psi of a heating system