For the winter we keep our lowest thermostate heat setting on 55 and I want to change it to 50 but my husband says that he heard if any lower than 55 the pipes can freeze or burst. Is this true or simply an old wives tale? What would be the least temperature with the least amount of worry? We usually keep the temps down to 55 for sleeping in the winter... can the pipes tolerate lower temps all day and all night long?

Assuming you are in F, it is the temp of the pipes, not the house, where are the pipes, are they in the walls, are they insulated, are they in a crawl space, a basement or where.

Water starts freezing at 32 degrees, so what is the outside temp for all of this,

I mean I keep my utility room at about 40 degrees, just above freezing, nothing in it freees.