how do i look after a kumquat tree?

I've never had a Kumquat plant before but it sounds like it's suffering from shock due to the change of climates.

I would suggest keeping it next to a window that receives the most light and keep the soil moist. My little orange tree is in a room with a deactivated radiator and is doing great; I would've thought they'd like similar conditions.

I agree. Plants are very sensitive to temp and environment change. Sometimes it's best to take the cellophane off a pot plant gradually over a couple of days to avoid shock. When I was little I bought my mum a Pointsettia and cycled home with it in the basket.....guess how long it lived!!! Give your plant some tlc and it should recover. Citrus need good light and can be stood outside from June to Sept.