Found a way to run coax through old ducts that actually worked

I had a job last week in a 1970s apartment building in Denver where the walls were all concrete block. No way to drill through them. The customer wanted cable in two bedrooms on opposite sides of the unit. I remembered an old HVAC guy told me once that some buildings have unused ventilation ducts from before they sealed things up. So I popped a register cover off in the hallway and sure enough there was a metal duct that went nowhere. I fed a glow rod through it and pulled both lines in about 15 minutes. But here is the debate part - some installers say running cable through ducts is against fire code or can mess with air flow. Others say if the duct is sealed off and not used it is fine. Does anyone else take shortcuts like this or do you stick to drilling through block every time?

2 comments

2 Comments

irisross13d ago

Jumped on this trick a few years back when I was running cable through an old warehouse. There was this sealed up duct from an old boiler system that hadn't been touched in decades. I popped a couple vent covers and ran coax for three security cameras through it in under an hour. The duct was completely dead ended so no air flow to worry about. I get why people say it's not code for active ducts but if it is sealed off you are just using empty space really. The building inspector actually saw it later and said it was fine as long as it was abandoned. Saved me from having to rent a hammer drill for the block walls in that place.

the_mia12d ago

Oh man that brings back a memory. I tried something similar in a old church building where they had these decorative metal ducts that were literally just for show, not hooked up to anything. I slid some Cat5e through there for the office remodel and it worked perfect until the pastor decided to hang a giant cross right where I needed to access the end cap. Still got the job done but had to fish blind for like 20 minutes with a coat hanger. Your inspector sounds way more chill than the one I dealt with later who made me pull it all back out because the duct was technically "accessible" even though nobody had touched it in 40 years.