On Tuesday, February 17, 2015 at 10:29:50 AM UTC-5, Ed Pawlowski wrote:
On 2/17/2015 1:13 AM, Tony Hwang wrote:

Hi,
Mod mid-efficiency furnace haad fresh air insulated dampered intake duct
for combustion. In this case intake can be inside the basement. Our
local code allows this.

CAN BE does not mean SHOULD BE.

Using outside air for combustion is more efficient. You are using air
that you paid to heat and sending it up the flue. Sounds to me the
contractor for the OP is just lazy.

The difference in heat may not be that great. One factor is where
the furnace is located, ie is it in the heated space, an unheated
basement, garage, attic, etc. Even assuming worse case, it's not
clear to me how much difference it makes. Yes heated air is used
for combustion. But the alternative, bringing in cold outside air,
just means less heat is generated in the furnace. You're getting
more heat of a furnace with 60F air going into it than with 20F air.

I know relatively new, circa 2007, expensive houses built here that
have furnaces in unfinished basements that use the basement air.