Fireplace Live HD Free is exactly as it sounds -- an app that will display a digital fireplace onscreen. It offers a handful of options for how to display that fireplace and the core functions are all free to use; but like most simulated fireplaces, windows, or other effects on the phone, the app has some issues related to the ads.
When you open the app it will automatically load to the default fire. You can tap the settings menu at any time to change between one of four different fire options. On newer iPhones you can switch to HD mode and there are some other functions like portrait mode and sleep timer. The sound can be changed as well depending on your mood and the entire app looks and operates nicely in an iOS 7-style interface. The one major drawback of the app is that there is an ad across the screen in the free version when the fire is active. For an app that is meant to simulate ambience and comfort, the effect is jarring and will be frustrating to the point that you may want to pay for the upgrade. If you only are interested in the sound and background imagery, however, the ad bar is thin and it doesn't impede the function of the app at all.
Overall, for a free app Fireplace Live HD Free is a great fireplace simulator that has a few options that similar apps don't offer. The ad is distracting if you want to spend time gazing into your phone; but otherwise, it works as advertised.