The DOE publishes a "Sizing Guideline" for VF appliances. They rank homes as loose, average and tight construction. As well they have them as t-stat equipped or not. In Zone V (coldest) they say an average construction, T-stat would take 3.85 btu/cu ft of space, so a 20x20x8=3200x3.85=12,320 btu. A Zone III (kinda Virginia,TN) would take 2.6 btu/cu ft or 8,320 btu.
Gas logs are listed as "decorative appliances". As Falcon said, they had a set they liked a lot in Houston. You get in trouble with them when you oversize them and run them to long and don't ventilate or keep the pilot assembly clean. The log manuf or seller never uses the sizing guidelines when selling VF logs. They roll them up and use them as pointer. Reason being, big flame sells. If they made a 10 kbtu log it would look like two bic lighters on low. If you want pretty, do buy the logs. If you want comfort I'd suggest a Rinnai Fan Convector in either the 510 or 824 model. Modulating gas valve, modulating blower, t-stat, quiet and cool to the touch. Pricey, but the best. Peterson is a good outfit, btw.