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I posted a version of this question on the LinkedIn RESNET/BPI group, and one or two members have commented that the blower fan would probably reduce the stack temperature slightly. That would be easy to verify with a bit of effort. Another member commented that it's probably a wash if the primary heating system is also gas-fired, and that system is making up the difference. If the primary is electric, you have to take the relative cost of electric into account.

At least one HI commented that lack of a blower fan is not an inspection report item.

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Of course. But even without the blower, there's quite a bit of convection going on. These things are designed to have air enter in the bottom, rise up the back, and flow out the front. The blower just increases the air flow. But does it increase it enough to have a measurable effect on overall heat transfer?

The difference between natural convection and forced convection is dramatic. I'm convinced there would be a big difference. It's the same idea behind a convection oven, which we know cooks food much faster than a regular oven.
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I'm not sure that's an accurate equivalence. Convection ovens break up that thin "insulating" layer of cooler air on the surface of the turkey.

Is what's being talked about really the same as a convection oven?

I honestly have no idea what is right in this case. If there's such a thing as common sense, common sense says a blower will take more heat off the exchanger and into the room, and reduce the stack temps.

I'm interested in what Fabry's test shows.

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. . . Another member commented that it's probably a wash if the primary heating system is also gas-fired, and that system is making up the difference. If the primary is electric, you have to take the relative cost of electric into account. . .

Why would the type of primary heating system make a difference? These fireplaces are uncoupled from the house.

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The difference between natural convection and forced convection is dramatic. I'm convinced there would be a big difference. It's the same idea behind a convection oven, which we know cooks food much faster than a regular oven.

Poor analogy. In a regular oven, there's pretty much no convection at all. In a direct vent gas fireplace, there's quite a bit of natural convection.

I have no doubt that increased air flow will take more heat from the fireplace enclosure. I just wonder if the amount of heat is significant.

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. . . Another member commented that it's probably a wash if the primary heating system is also gas-fired, and that system is making up the difference. If the primary is electric, you have to take the relative cost of electric into account. . .

Why would the type of primary heating system make a difference? These fireplaces are uncoupled from the house.

Because I doubt the efficiency of the gas fireplace in providing heat to the house would match the gas powered heating system.

Marc

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. . . Another member commented that it's probably a wash if the primary heating system is also gas-fired, and that system is making up the difference. If the primary is electric, you have to take the relative cost of electric into account. . .

Why would the type of primary heating system make a difference? These fireplaces are uncoupled from the house.

Because I doubt the efficiency of the gas fireplace in providing heat to the house would match the gas powered heating system.

Marc

Obviously.

I guess I'm really not concerned with the question of whether or not these things provide an economic way to heat a house or supplement an existing heating system. There's little doubt that they don't. I'm just curious about whether or not a blower makes one of these things significantly more efficient that it would be without one.

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Obviously.

I guess I'm really not concerned with the question of whether or not these things provide an economic way to heat a house or supplement an existing heating system. There's little doubt that they don't. I'm just curious about whether or not a blower makes one of these things significantly more efficient that it would be without one.

Improving efficiency means diverting a greater portion of the developed BTU/hr from the stack to the room, over and beyond what the natural draft alone would accomplish. Sounds like that's a question of whether that little blower actually increases the air flow over and beyond what a natural draft would create.

I guess we'll have to wait on Chad's report.

Marc

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