Most fireplace mantels will help deflect the heat from above the fireplace. If you have a wood burning fireplace be aware that the ash created will increase the need for the TV to be cleaned regularly and the heat vents will need to be checked for dust build up.
Samsung LED TVs have an operating temperature range of 50° F to 104° F (10° C to 40° C). Temperatures outside this ranges will affect the operation of the TVs and can cause damage. Consequently, you can mount your LED TV over a working fireplace or a heater so long as the tempture where the TV is mounted does not exceed the operating tempurature range.
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