In the winter should you heat a low/dirt floor crawl space with a furnace vent?
In buying a old house with a low/dirt floor crawl space and plumbing under the home, would heating the part of the plumbing area cause any mold or other problems in the winter?
No, its quite the contrary. Heating a crawlspace will prevent mold. But heating a dirt floor crawlspace without taking any steps towards insulating the crawlspace and creating an air seal is going to cost dearly, so there are a few things I would do first to prevent heat loss, air leakage, moisture damage and mold. This page here will have most of the answers you need –
Best Practices for Insulating Crawlspaces
So here are a few questions that will help us get you more specific answers about how to best proceed:
There are two main ways to insulate a crawlspace floor, either you can separate it and keep it cool, or treat is as part of the conditioned space and keep it warm. Where your plumbing is may help determine which is best for you, as well as what your budget is for the work that you may perform. To be clear- we don’t perform work so I’m not trying to tap into your budget to fill it, just trying to find the best path forward for you. Insulating it would be best, that could be either between the joists, or also insulating the floor.