I disagree. Most rack units are designed for heated rooms that are maintained at the desired ambient temp. This is why they just come with a strip of heat tape for the hot spot. T8s and similar enclosures allow you to put a heat source (such as an RHP) inside to maintain ambient temp as well as using heat tape for a hotspot (or using the RHP for a hotspot and letting it heat the cool side to desired ambient - this only works sometimes...).
I have heard of some AP racks now coming with an RHP side mounted for ambient temp, but I'm not sure how well that works or how it's implemented.
Either way, cold house = use enclosures, not a rack. *edit* Unless, as Neal said, you can use a space heater to heat just the room your snake is in.