We live in a very old house with an unfinished basement. The heat for the entire main floor is from a furnace in that basement that blows through the square style ductwork to vents placed in each room on the main floor. These ducts have no insulation on them at all, and get quite warm to the touch near the furnace itself, but decay with distance (obviously). Right now our water heater is wrapped with probably pretty old insulation - I don't see any labels on it, but it's the yellow style with a white paper backing. It's held to the water heater with duct tape. We have a water heater insulation tube recently purchased, and are wondering if we could repurpose the fiberglass insulation on the ductwork.
The two main concerns we have come up with are:
- Overheating the insulation --> starting a fire.
- The insulation somehow makes its way into the duct through some tiny crack (currently we have the fancy duct tape for heating vents around all the cracks, but this is likely imperfect) and gets into our air.
We think these are both unlikely but wanted to ask. Having trouble finding this exact question on the internet. We know this is not an optimal solution, but it's available now and free, so our main concern is safety. Can we get away with this, or is it critical to purchase the foil-backed insulation for use with duct work for heat?
If it matters, these ducts only connect to the furnance; there isn't any air conditioning set up in this house, which was built in the early 1800s (for sure before 1830).