An electric fireplace is a fantastic addition to your home. It's clean, decorative and energy-efficient, and will get you through those brisk fall and winter nights in comfort and style. There are many different brands that offer electric fireplace installation kits, so you'll want to check with the manufacturer's instruction booklet for specific details on how to properly place your specific device. But if you've got a traditional fireplace in your home that you'll be replacing, here's how you'll want to go about installing your new electric fireplace.
Your old, traditional fireplace is not a detriment to your new electric model. In fact, if the electric fireplace unit will fit inside your old fireplace, you can simply repurpose your existing hearth. But you should certainly close off the chimney. You won't be using it anymore, and open chimneys let the chill drafts of winter inside, the exact thing you're trying to prevent. Do a quick online search and you'll find several sites that will walk you through the process of closing off traditional chimneys.
Whether you use your existing hearth or construct a new one is entirely up to you. Electric fireplaces are considered "zero clearance" devices, as they don't produce a flame or require any sort of venting through a chimney or flute. So you can choose to place it in your previous fireplace, or simply close it off and construct a new one wherever you desire. But chances are you'll want to put your electric fireplace in roughly the same position as your old one, or that you didn't have any sort of fireplace to begin with. In both situations, you'll need to construct a hearth.
That means it's time to break out the measuring tape. Measure the floor directly in front of your existing hearth and build a 2x4, U-shaped frame around the hearth's opening. Again, height and ventilation do not matter, so you can build this new hearth as large or small as you want. But you should build it high enough to allow for clearance underneath for the electric cabling. Once the area is framed out, reinforce the inside corners with triangular blocks, then screw the new frame into the floor. Cut a plywood board to fit over your new 2x4 frame, extending it backwards so it rests within the existing fireplace, or against the wall if no fireplace exists. Level the top board and use construction adhesive to lock it in place. Now you've got the beginnings of your new hearth. Apply molding along the edges to give it a more finished look.
Now that you've got your hearth in place, look to your electric fireplace's instruction manual and locate the mounting hardware. You'll want to test the fit before final attachment, and make sure the whole thing is level. Once you're clear on the positioning you'll need to cut an access hole in the hearth so you can run the electric fireplace's plug and cord through the back. Drill or chisel through the existing fireplace or back wall as necessary, then route the wiring through the hole to the closest outlet. Now you can reinstall the firebox on top of the hearth. Make sure you take full measurements of the firebox, so you can construct a mantel and surround that fit your décor. Once all is in place, 2x4s will finish framing the top and sides of the firebox. Then you're ready to install the electric fireplace. The strategy will be similar with corner electric fireplaces, but the measurements will of course be different. Have the wood professionally cut to the right specifications if you want to insure a proper fit.