You've probably heard that older style, open masonry wood fireplaces can lose more heat than they provide, but there are ways to address those problems. Here's a few options you might want to consider, gain real benefits from your fireplace, and maybe save a little money too:
- Keep the hot side hot / cold side cold. One of the biggest issues with an open fireplace is that they can be extremely drafty. When not in use, find a way to keep your warm indoor air from literally going up the chimney. A piece of batt insulation behind the flue opening or a chimney balloon can be a good way to close the draft - just remember to remove if you actually build a fire.
- Open a window. As counter-intuitive as this may seem, providing a small level of outdoor air for combustion (such as opening a window slightly in the same room and closing off the room from the rest of the house) can help prevent warm air in the rest of your home from being pulled out the chimney while a fire is burning and your flue is open. This option is intended for those looking for ambiance from their fireplace - not heat. Alternatives exist to create a separate air intake that performs the same function without closing off from the rest of the house, but this is a more expensive approach.
- Glass doors. A modest step towards keeping warm air from being pulled from other rooms. Inexpensive and easy to install. However, this is also more of a fix when the fireplace is used for ambiance as opposed to gaining any real heating efficiency.
- Inserts and hearth stoves. There are a wide variety of choices (and prices) for installing a "closed" system that will preserve the heat created from a fire and put it into the living space. These can be as simple as installing a "heat exchanger" that captures the heat and uses a fan to push it into your living area, a "stove" that sits on the hearth and makes use of your existing chimney, or even a fully enclosed firebox that is installed in the existing opening (this last choice usually being the most efficient - but also the priciest).
For more info on inserts, check out these websites: