This reconstruction of a Viking house in Schleswig is from an article on Open Hearths, Ovens and Fireplaces. Among other topics, it reviews studies in how much wood it takes to heat reconstructed Viking dwellings. Conclusion? No one could have lived in the famous long houses during the winter. They required far too many tons of fuel for medieval woodcutting technology to meet. In contrast much smaller houses, like the one here, are bearable—for modern graduate students, at any rate.
Historical fiction and fantasy writers take note: if you want a feast in the Great Long House, set it in the warmer months. If you want to imagine dwellings, make them smaller. For an evocative two-minute tour of the Hedeby (Haithabu) reconstructed countryside and town, click here.