Which type of pipe should not be used for connectors passing through an unheated space?

The use of single-wall pipe in unheated spaces is discouraged primarily because it lacks sufficient insulation and may not adequately prevent condensation or freezing in colder conditions. Single-wall pipes are typically more susceptible to temperature fluctuations, which can lead to moisture accumulation on the outside of the pipe. This is particularly problematic in unheated areas, where the risk of freezing and potential damage to the system increases.

In contrast, double-wall and vented pipes are designed with additional insulation and protective features that help maintain appropriate temperatures inside the pipes and reduce the risk of condensation forming. Flexible pipes also typically have better insulating properties that allow them to perform safely in various conditions, including unheated spaces.