A friend of my husband’s installed our inexpensive home theater system as a favor. He has the wires for the speakers (mounted around the room) coming up out of the vents in the floor. Granted, the vents are in a good spot for speaker placement. But is this a fire hazard?
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Some heating vents can get pretty hot, which may cause the insulation on the wires to melt or become brittle over time. Should the wires melt or the insulation crack off, i belive that there is a higher chance of the speakers themselves shorting out than the wires sparking and causing a fire. However the risk is still there.
As a firefighter myself, it is not a chance i’d take.
rubber/plastic melts at a higher temperature than the heat in your vent (the wire should show up to what temp it can withstand and mine is up to 176F). Plus its in a metal vent so it can’t spark and ignite something unless you have tons of dust down. the risk factor is about a .2 on a scale of 100. For more assurance though you can buy some wire insulation and put it over it.
My suggestion is to turn on the system, and the heat to see just how hot it gets, at the wire. If you used what wiring came in the box you could be headed for trouble with resistance, as temperature is a coefficient of resistance. If when the system is on for a while and the heat is on you can feel the wiring and it is warm to the touch then you have a serious safety issue. Just being in the vents raises the probability but again you have certain safeguards in place already.
If you use the proper rated in wall cable you will not have issue. to be safe pick a bigger gage as well, Sonic quality is a function of cable impedance and the temp coefficient comes in play. This is why most serious installs avoid temperature variations like your duct.
If it is concerning you you could run them under a area rug. Look at how a store has a living room set up to see what I mean.
You don’t have to worry about fire hazard the worst that would happen is some discoloration on the outer insulation of the speaker wires……I’ve had my speaker wires lying on top of heat vents in the past and no fires.
Under most circumstances the risk of fire due to a short in loudspeaker cables is virtually non-existent.
If your loudspeaker cables use the typical PVC insulation found on most lower-cost or generic A/V cabling then you do run a somewhat higher risk of developing a problem. Prolonged or repeated exposure to elevated temperature and airflow rates can, over time, result in degradation of the PVC insulation in large part due to plasticizer migration and volatility. This can lead to increased brittleness and crazing in the exposed portion of the insulation, which could eventually result in failure of the insulation.
Under these circumstances the most likely result is that the protection circuit that protects the output stage of the audio amplifier would kick-in, or worse, the output stage of the amplifier could self-destruct; depending on how well the unit was designed and built. There are very few (well-designed) audio amplifiers that would pose a fire hazard when the speaker outputs are shorted.
You have a couple of fairly simple choices to effectively mitigate the threat of potential problems: (1) replace the loudspeaker cabling with either a jacketed loudspeaker cabling or use polyolefin (i.e., polypropylene) insulated cables; or (2) install 1/2″ to 1″ diameter plenum rated or riser-rated halogen-free (aka low smoke zero halogen or LSZH) nonmetallic corrugated flexible conduit (aka “innerduct,”) over the (speaker) cabling wherever the cabling passes through the air ducting. Electrical and datacom/telecom suppliers, better hardware stores and A/V dealers/installers should have innerduct in stock.
One last item – you can reduce the amount of self-heating that occurs with higher cable resistances by choosing loudspeaker cabling that has a larger wire gauge. Speaker cabling is generally available in stock wire gauge sizes ranging from 4 AWG up to 16 AWG and higher; the lower the number the larger the gauge of wire. As a general rule of thumb you should always use the lowest wire gauge you can afford and never less than a single run of 14 AWG cable. Though rarely a significant issue, self-heating varies in direct proportion to the cable’s resistance, (which increases as the wire gauge decreases, i.e., smaller overall conductor cross-sectional area and/or the cable length increases,) the impedance of the loudspeaker and the power output of the audio amplifier.
Carlon Product Brochures Index
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Hal-Free Riser-Gard® Nonmetallic Corrugated Flexible Conduit
http://www.carlon.com/Master%20Catalog/Flexible_Raceway_Brochure.pdf
Belden Low Smoke Zero Halogen Speaker Wire and Cable
http://www.belden.com/search/index.cfm?q=halogen+AND+speaker
Understanding In-wall Speaker, Video and Audio Cable Ratings
http://www.bluejeanscable.com/articles/inwallrating.htm
Cabling What You Don’t Know Can Kill You
http://www.wireville.com/news/Cabling%20Can%20Kill%20You.html
Cabling Safety in Multi-Story Structures
http://www.wireville.com/news/Cabling%20Safety%20in%20Multi-Story%20Structures.pdf
Wire Management and Life Safety Articles
http://www.hhrobertson.com/ls_docs.cfm
Guide to Low-Voltage and Limited-Energy Systems
http://www.mikeholt.com/documents/lowvoltage/pdf/LowVoltBook.pdf