Recently finished upgrading to a 200A panel and replacing all the
wiring in the house. Instead of Al entrance cable I used 2" conduit
to get from the meter to the panel and ran copper feeds to the panel.
The electric company replaced my old ham slicer meter with a digital
meter.

First, can I putty or caulk around the wires inside the conduit to
stop the cold air from coming in?

This is actually required by the NEC (300.7-A). Mix of warm and cold air
can condense the moisture out of the warm air producing water. The common
building entry is for conduit down from the meter can to an LB fitting and
conduit out the back into the building. Common practice is to pack "Duct
seal" (a UL listed a commercial product) around the wires inside the LB
where they go into the conduit into the building. Also common practice
around here to hacksaw a small slot in the bottom of the LB to drain water
if any accumulates.


Second, my electric bill is up about 15% since I started. The only
additional load I added was six 75watt bulbs on two dimmers that
replaced one 100watt table lamp, these run 16 hours a day. Also three
hard-wired smoke detectors. Are the digital meters more accurate? Is
there a way I can test the meter?

The digital and mechanical meters should both be very accurate. You can
shut everything off except for a known wattage and read the meter before
and after a timed interval. A 1,000 W load for 1 hour will register 1 KWH.
For real accuracy you would probably have to check the "known" load with
something like a "Kill A Watt" meter
http://www.p3international.com/produ.../P4400-CE.html



*Bud is correct about the Duct Seal. I think it the best way to go because
it can be removed years later if needed. I've drilled holes in weatherproof
boxes to let water drain out, but eventually they become clogged with crud
and water accumulates anyway. If you're so inclined you can open the LB
every year and clean out any condensation. Have an extra gasket standing
by. You can also pack some Duct Seal inside of the weatherhead to prevent
rain from getting in. I also caulk around the fittings and the hub.

If you think that there is a problem with the new meter, you should ask the
power company for a replacement. However you did increase your load by 350
watts which is on 16 hours a day. Do you have a day rate and a night rate
with the new meter? I have Time of Day Service for my electric and
consequently have a higher rate during the day than at night and on
weekends.