An open wood burning fireplace consumes a lot of excess air which is air that is in the house and has been heated to the present room temperature. This air must be replaced by cold, outside air. The net effect on the temperature of the house is that it gets colder by using an open wood-burning fireplace. You may be nice and warm next to the fire, but rooms away from the fireplace are getting colder as the outside air is drawn in to make-up for the excess combustion air that the open fireplace is using.

A heat grate/heat exchanger is a waste of money unless in is paired with a set of glass doors. The doors minimize the amount of excess combustion air consumed by the fireplace. An open fireplace (no glass doors) with a heat exchanger still has the problems of an open fireplace noted above. Save the $500 and put it towards an insert.

The best way to get heat from a woodburning fireplace is to install a good insert. The insert eliminates the excess combustion air, burns less wood more efficiently, and usually has a fan to blow hot air out of its vents.

The trick of running the furnace fan to disperse the heat throughout the house doesn't work in many cases as it depends on the layout of the house. My wife immediately picked up on the fact that cold air was coming of the furnace vents on the second floor as I ran the fireplace on the first floor. I use the furnace fan in the summer but not winter.

Gary;
I have an open fireplace and when it is lit, it makes the house colder, just like you described. I'd like to find a way to make the fireplace work without having to expend about $3,000 for an insert or woodstove plus the required flue liner.

Would glass doors prevent the cold house effect?

I remember fireplaces with glass doors when I was a kid. To get any heat, the glass doors had to be opened. Is there any way to get heat out of the fireplace with closed glass doors? Does enough heat radiate off closed glass doors to heat a room or more?

Why does an insert heat better than just glass doors? Afterall, the insert needs to draw the house's air too. And it is just a firebox in a fireplace which itself is kind of like a firebox.

What makes an effective insert? Should it be made of cast iron or steel? Is the insert with a bay front a better design than the flat front because it has more radiant area?

Thanks. \HH

HH:

I am no expert by any means, just a homeowner trying to get heat out of his masonry fireplace. I have experience with only one insert - my own. Here's my best shot at your questions:

"Would glass doors prevent the cold house effect?"
Yes, the glass doors would prevent the cold house effect of an open burning fireplace by eliminating the excess combustion air that is consumed by the fire.

"Is there any way to get heat out of the fireplace with closed glass doors? Does enough heat radiate off closed glass doors to heat a room or more?"
The problem with getting heat from a fireplace with closed glass doors is the glass itself. Most glass doors are made of tempered safety glass which does not allow UV rays to pass through and provide heat. This is why I made the comment in a previous post to possibly combine the grate heater with a set of glass doors. The glass doors in most quality inserts are made from ceramic glass which allows UV rays to pass through. Some glass door manufacturers use ceramic glass, but it can be very expensive. I do not know if a set of ceramic doors would provide enough UV energy to heat a room (I wouldn't think so, but it's just my opinion).

"Why does an insert heat better than just glass doors? Afterall, the insert needs to draw the house's air too. And it is just a firebox in a fireplace which itself is kind of like a firebox".
An insert heats better because it is made to extract heat from the fireplace (the glass doors alone are made more for looks or when the fire is burning down to prevent smoke from coming back into the room). Similar to a set of glass doors, it controls the combustion air for the fire by providing just enough air to feed and maintain the burn (an adjusting lever controls the intake air flow). The insert eliminates the excess combustion air that makes a room cold since cold outside air must replace the excess combustion air. As previously noted, most quality inserts use ceramic glass in the doors. Most inserts have at least one fan that draws separate room air into the non-combustion passages of the unit, circulates the air around the passages, heats the air, and sends it out of the discharge vents at high temperatures. Inserts that do not have a fan rely on natural conduction from the hot surfaces of the insert to release heat into the air. Inserts that are EPA-certified also have a "post-combustion" zone which further burns the gasses from the wood to provide a cleaner burn and as well as additional btu's compared to burning only the wood. Last year, I measured the temperature of the heated room air from the discharge vents of my insert using a multi-meter with a thermocouple attachment. I measured a max temperature of 348 degrees F at the vent, 280 degrees F at one inch from the vent, and 148 degrees F at two inches from the vent. I get decent heat out of my unit.

"What makes an effective insert? Should it be made of cast iron or steel? Is the insert with a bay front a better design than the flat front because it has more radiant area?"
I only have experience with my own insert so I don't think that I can provide a good response. Maybe you can make a separate post for this question. I would want a variable speed fan that is fairly quiet. My fan can run in "blow dryer" mode if I choose to but it is fairly loud at blow dryer speed so I keep it at medium speed. I think that the bay front may add more room to the firebox (not sure about this), and may provide a surface area to keep a pot of water so that humidity can be added to the room (plus more surface area as you noted). It is a nice look but you need additional hearth floor area under the bay.

I hope my answers helped you.

One of the best things you can do to help get heat out of a fireplace is install, if possible, vents in the firebox that allows it to draw combustion air from outside.

Friends have a fireplace like this -- a pipe in the back of the firebox with a damper on it. It looks like the vents on a Weber cooker kettle, only made of heay cast iron.

Paired with a heat recover grate with a blower and glass doors they get a lot of heat out of their fireplace without cooling off the rest of the house.

They can do a pretty good job of heating their 2-story great room (about 15x25) with just the fireplace.

They only have to kick the heat on in the great room on the coldest, windiest days.

As to the question regarding glass doors:
As far as I know, the glass doors must be open when the fire is operating, otherwise they can explode. (See the post from last year where someone's actually did that)
The glass doors are only for when shutting down the fire.

The ceramic doors on our 2 sided insert provide some good radiant heat. The air flow system and the fact that the draw air comes from outside make it a nice little heat source for the house.