Heating 22x20 attached Garage

[Inca32]

I have a 22x20 attached garage, insulated, 10 foot ceiling, 4 post lift 3 classic cars. I have a sears 40K direct vent wall heater 30 years old that is done for. It’s the tall one, 16 inches wide. Williams is makes the only one that would be a direct replacement at 50K BTU. Would a Rannai unit of 11K BTU be an option or would I have to go a 18K or larger.
On it gets wider than 20 inches it would be blowing near the rear of a car. Also ceiling is not an option because of a pull down stairway and lights on opposite side of 4 post lift.
I am in the Detroit area so winters do get cool.

 

[nadogail]

Was the original heater adequate for its purpose?

If so, IMHO, The Williams should be a suitable replacement. I have seen several Williams heaters that were very well regarded.

A consultation with a professional who is familiar with your local environment will be worthwhile.

 

[cpttuna]

I have a 60,000 bTU mobile home furnace heating my 24x20 garage.

 

[Jackfre]

For Detroit, at 400 sq ft you may be okay with an 11, but the 17 will give you a 50% boost of the top end and start-up and the low end is 8200 vs the low of 5500 on the 11. Another thing, given that the 11 is more of a vertical configuration you have less wiggle room on the vent location. The 17, 22 & 38 give you more latitude in vent location and that can help with snow clearance.

 

[arindom]

Awesome...!!!!

 

[nafterclifen]

I'm in NE PA. I heat my 22x20 attached garage, insulated, 9' ceilings with a 7,500W 240V heater which is just over 25k BTU. Works great and is more than sufficient. I keep it on low and it maintains about 65 in the winter. I can't imagine 40k BTU. You could probably leave an overhead door open and still maintain 60+ with something like that running on high.