Fireplace Blower

[redpoint5]

I'm not sure how much a blower fan can increase the efficiency of a natural gas fireplace, but it seems like it would help extract at least some energy that would otherwise go out the exhaust.

My house has 2 identical 12,600-18,000 BTU gas fireplaces. One has a blower and the other does not, though there is electrical already installed.

The squirrel cage blower consumes 56 watts and is moderately noisy to run. I think these are typically rated to 130 CFM. My high school electronics teacher said squirrel cage blowers aren't very efficient.

As a proof of concept, I rounded up all the spare PC cooling fans I could find and set them into the intake of the fireplace. The 4 fans (3x 160mm, 1x 120mm) consumed 6 watts, was whisper quiet, and seemed to move about half the air.

I could purchase a purpose built squirrel cage blower with rheostat and temperature switch for $60, or I could purchase 6x 120mm fans for around the same price. I'm thinking if I mounted 6x 120mm fans, I could get equivalent air movement for 18 watts.

Amazon link

[oil pan 4]

I use energy start quiet bathroom fans.
I don't know how many watts the 4 inch quiet fans draw but they move a lot of air.

[Hersbird]

Our old 1940's brick, wood burning, fireplace has a natural circulation setup where it pulls cold air off the floor, runs it through 4 thick walled 4" pipes behind and over the burn chamber, and then dumps them out about chest high in the room. It's neat to get it rocking and actually feel the air "blowing" out those pipes even though there is no fan, just natural heat rise.

So in your case, I wonder if you actually blew those fans into the back, beside, and over the insert, with the hottest air coming out the top would take better advantage of natural heat rising.

Edit- I see that's exactly what you are doing already!

[freebeard]

As a proof of concept, I rounded up all the spare PC cooling fans I could find... and seemed to move about half the air.

So you're halfway there. Fabricate a log manifold (no pun!) to manage the airflow. Maybe get some matching fans?

When I worked at Nextstep electronics recycling, I started out in the warehouse, dismantling. I tore apart an Olivetti PC from the 1970s that was way overbuilt (the thing had three motherboards!). It had a [six inch in metric] cooling fan with a cast aluminum body. It would replace any two of the ones you show. Prolly still around here somewhere, it turned into sort of a souvenir.

[Piotrsko]

Need maybe 4 more of the big ones to fill the gap. You're losing pressure out the front sides. Better heat transfer efficiency will occur if you slow flow through the system a bit.

[redpoint5]

Originally Posted by Piotrsko

Need maybe 4 more of the big ones to fill the gap. You're losing pressure out the front sides. Better heat transfer efficiency will occur if you slow flow through the system a bit.

6 of the 120mm fans would just about fill the width, and would fully fill the height. I'd make some frame that blocks off any gaps.

I wonder why fans seem to be an afterthought to these fireplaces? It would be a simple matter to have a fully ducted and sealed system that draws air from the bottom and sends it around through the top. The fans themselves could be mounted to the grate in front so they are out of the way when accessing the gas controls, and would be easy to service if one went out. Plus those computer cooling fans are stinkin cheap.

At any rate, I've decided to buy a purpose built fan since it has a speed controller and thermostat switch built in.

[freebeard]

It would be a simple matter to have a fully ducted and sealed system that draws air from the bottom and sends it around through the top.

Exactly describes my friend's fireplace. I've helped them pull the sheet metal insert and re-grout the firebrick, twice.

Originally Posted by Piotrsko

Better heat transfer efficiency will occur if you slow flow through the system a bit.

I suggested a manifold. It could be a cap across the full width with a single fan at each end. This would slow the airflow and stop reversion.

[redpoint5]

I knew the price was too good to be true at $60. The fan I received uses bushings despite being advertised as ball bearing, and arrived sans thermostat. I’m sending it back, which means I’m contemplating my own setup again. I need to find an outlet switch that can be closed via thermostat.

[Hersbird]

My grandpa gave me a home made electric smoker that has a thermostat that controls an outlet you plug the cheap hot plate into. Otherwise it's just an old BBQ. It holds temperature as well as the digital smoker I bought last year.

[Piotrsko]

I use an old Airconditioning thermostat on the cool Side since that is the logic I need and the thermostat mercury switch is rated for 1/2 hp and never arcs the contacts shut. I have a newer one that has similar rated relays, plus the setback timer feature. Maybe $5 @ habitat for humanity