Why does the glass on my fireplace fog up when I turn it on?

There is a temperature difference between the air inside of the fireplace and the air in the room. Warmer air has more moisture than cooler air. When the fireplace is turned on, the temperature inside the fireplace begins to warm up and condensation forms on the cooler glass. The water vapor in the warmer air is condensing on the cooler surface. As the fire gets hotter, usually within a few minutes, the glass will clear. Although it can be a bit annoying, this is not uncommon and really nothing to be concerned about.

Below is a list of fireplace and grill stores that service Ontario (ON)

Ajax, ON Topfire Fireplace and Barbecue Inc. 487 Westney Rd. S Ajax, ON L1S 6W8		Visit Store Page
Aurora, ON Topfire Fireplace and Barbecue Inc. 15483 Yonge St., Unit 1C Aurora, ON L4G 1P3		Visit Store Page
Belleville, ON Friendly Fires 69, Dundas East Belleville, ON K8N 1B9		Visit Store Page
Burlington, ON Barbecues Galore 3100 Harvester Road Burlington, ON L7N 3W8		Visit Store Page
Cambridge, ON Bast Home Comfort Inc. 471 Hespeler Rd. Cambridge, ON N1R 6J2		Visit Store Page
Carleton Place, ON Friendly Fires 11384 Highway 7 Carleton Place, ON K7C 3P1		Visit Store Page
Cobourg, ON Friendly Fires 70 King Street East Cobourg, ON K9A 1K9		Visit Store Page
Collingwood, ON Chantico Fireplace Gallery Inc 209784 Hwy 26 Blue Mountains, ON L9Y 0L8		Visit Store Page
Concord, ON The Fireplace Specialist 19-391 Edgeley Blvd. Concord, ON L4K 4A7
Etobicoke, ON Barbecues Galore 1470 The Queensway Etobicoke, ON M8Z 1T5		Visit Store Page
Goderich, ON Huron Fireplaces 308 Huron Rd Goderich, ON N7A 3A2
Hamilton, ON Chadwicks & Hacks 682 Fennell Avenue East Hamilton, ON L8V 1V4		Visit Store Page
Huntsville, ON The Fireplace King inc. 14 Howland Drive, Unit 1 Huntsville, ON P1H1M3
Kincardine, ON Chantico Fireplace Gallery Inc 6 Ashfield-Huron Kincardine, ON N2Z 2X3		Visit Store Page
Kingston, ON Friendly Fires 271 Dalton Ave. Kingston, ON K7K 6Z1		Visit Store Page
London, ON Porky's BBQ & Leisure 1075 Sarnia Road London, ON N6H 5J9		Visit Store Page
Markham, ON Kastle Fireplace LTD 8294 York Durham Line Markham, ON L0H 1J0		Visit Store Page
Meaford, ON Chantico Fireplace Gallery Inc 158185 7th Line Meaford, ON N4L 1W5		Visit Store Page
Mississauga, ON Ontario Hearth Fireplaces 3425 Laird Road Unit #2 Mississauga, ON L5L 5R8		Visit Store Page
Niagara Falls, ON The One Stop Fireplace Shop LTD 4332 Drummond Road Niagara Falls, ON L2E 6C3		Visit Store Page
North York, ON The Fireplace Company 2854 Dufferin St. North York, ON M6B 3S3
Oakville, ON Barbecues Galore 490 Speers Road Oakville, ON L6K 2G3		Visit Store Page
Orangeville, ON Its in the Shed 7 Little York Street Orangeville, ON L9W 1L8
Ottawa, ON Capital BBQ 12 Grenfell Crescent Ottawa, ON K2G 0G2		Visit Store Page
Pembroke, ON Performance Woodburning & Gas 204 Boundary Road East Pembroke, ON K8A 6W4
Penetanguishene, ON Home & Cottage Centre 4 Centennial Drive Penetanguishene, ON L9M 1G8		Visit Store Page
Peterborough, ON Friendly Fires 971 Highway 7 Peterborough, ON K9J 6X7		Visit Store Page
Sarnia, ON A Village Fireplace Shop Ltd. 623 Broadway St Wyoming, ON N0N1T0		Visit Store Page
Stratford, ON Tri-County Brick 320 Home st. Stratford, ON N5A 7C9		Visit Store Page
Sudbury, ON Nordic Energy Systems LTD 2324 Long Lake Road Sudbury, ON P3E 5H4		Visit Store Page
Thunder Bay, ON Bob's Woodburners & Fireplaces 803 Memorial Avenue Thunder Bay, ON P7E 3Z7		Visit Store Page
Toronto, ON Marsh's Stoves & Fireplaces 3322 Dundas Street W Toronto, ON M6P 2A4		Visit Store Page
Waterloo, ON Bast Home Comfort Inc. 12-620 Davenport Road Waterloo, ON N2V 2C2		Visit Store Page
Windsor, ON Scott's Fireplace Select, Inc. 2 North Talbot Road Maidstone, ON N0R 1K0		Visit Store Page