Retrofit Larger Blower Fan???

[Murphy2000]

I folks,
I have an Enviro Venice 1700 Wood Fireplace Insert and I've noticed that the blower fan doesn't put out much volume.. I think the fan is rated at 135 cfm's or something like that.

Anyhow, as an engineer, it seems to me that a larger blower fan pushing something in the 300 cfm range would make the stove much more efficient in that it would scrub more heat from the fire box.

The original stove fan is a double wheel type where the wheels are about 3 inches wide and about 2.25 inches diameter and the motor sits between them. The configuration (small diameter wheels) obviously puts more emphasis on output volume rather than static head pressure.

There isn't enough room to physically mount another fan to the stove so it would have to be placed near the stove and ducted in separately. The current fan is sort of integral.

I was thinking of cutting a hole in the air jacket sheet metal that surrounds the stove and doing some HVAC work to run a duct to an external fan placed nearby. The hole would be on the same side as the blower but placed behind the stove surround. My fireplace brick setup has an old "heat-o-later) installation that includes a small closeted space just off to the side of the brick. The old setup had a large fan in there and duct work already in place. Heck, there's so much room to work with, I could even integrate an air filter setup like a standard furnace has.

Is there anything I am not considering that I should be considering? Anything that you folks think I might have forgotten or not realized?

Link to the stove I have:
http://www.enviro.com/fireplace-products/wood/fireplace-insert.html#venicebig

Actual photo of installation

Thanks!

 

[pen]

Any modification to the unit may void it's UL listing, and cause an issue with the insurance company in the event of a claim and / or a code inspector during a sale.

Additionally, if you pull too much heat away from the fire, you will actually hurt things by creating a cold feeling airflow (more air but less temp to it) and may actually decrease the quality of the burn, as a hot firebox will keep the fire burning at cleaner more consistent pace.

It doesn't appear that you have much wood in the stove, is that how you generally load it? Or were you burning down coals?

pen

 

[Murphy2000]

How I load depends on how I want it to burn which depends on how much heat I want for how long..
It also depends on what kind of wood I'm burning..

I know I need to make sure I don't pull too much heat from the fire box, but I'm not sure how sensitive that issue would be since it is just air and air doesn't carry a lot of energy.

When standing or kneeling three feet in front of the stove, the heat you feel is radiant heat, not the convection heat the blower creates. To feel the blower, you have to put your hand within 4 or 5 inches in front of the discharge vents at the top..

 

[rwhite]

I think you'll be defeating the purpose of a radiant heater. Essentially turning your radiant heater into a not so effecient forced air furnace. The purpose of the fans on inserts is to prevent overheating inside the firebox. Just enough air flow to allow the exposed portions to maintain a higher heat and radiate it out. The faster you move the air the more it cools the entire stove. As long as I'm not overheating the stove I run my fan as low as possible (barely audible) and get the best results. If I start to overheat the stove I can cool it doen it a hurry by cranking the fan speed to high (and I have a 125 cfm blower).

 

[Bones]

I think you'll be defeating the purpose of a radiant heater. Essentially turning your radiant heater into a not so effecient forced air furnace. The purpose of the fans on inserts is to prevent overheating inside the firebox. Just enough air flow to allow the exposed portions to maintain a higher heat and radiate it out. The faster you move the air the more it cools the entire stove. As long as I'm not overheating the stove I run my fan as low as possible (barely audible) and get the best results. If I start to overheat the stove I can cool it doen it a hurry by cranking the fan speed to high (and I have a 125 cfm blower).

I agree...it will be a waste of time and effort, plus the noise factor. I run mine on medium to low settings.

I used expanded metal for my surround which has helped to gain a little extra heat output.

 

[Bluezx636]

I also get best results running my blowers at 1/3 speed. Like Pen said, I have noticed if I run the blowers too high it with cool my Clydesdale off to much and weaken the secondary burn which directly effects heat output.

 

[Murphy2000]

For those with fireplace inserts and blowers..
When you run your stove on high, how hot is the air coming out the blower vents?
Can you hold your hand two or three inches in front of the vent for 5 seconds?
By any chance do you know what the actual air temperature is coming out of the vents?

How many CFM's are your blowers?

What you guys are saying does not coincide with what I am observing and I am wondering where the discrepancy is coming from..

 

[madison]

Try cleaning out the "squirrel cage" (blower impeller fan) they clog with fine dust - especially if you have had interior painting or sheet rock work (1st hand experience with the same issue)

I agree efficient (low wattage) air flow over the heat exchanger (stove) will increase the BTU output.

 

[valley ranch]

At our Nevada place I run the fan on pretty high. You might install a variable resistor, that way you can adjust to your liking, or turn it off and use the internal fan, when you see fit.
If you decide to do that mod, show us how you do it. Thanks Richard


An after thought. On the stove here in the mountains, I installed a fan from an old microwave in the SpiroFlo heat exchanger on top of the stove. The fan that came with it was slow and noisy. I'm very pleased with the way it works.

 

[jotulguy]

I just noticed you mentioned running your stove on high. If your air is wide open the heat output will be limited. Maybe that's the issue here rather then the fan it's self.

 

[Murphy2000]

The problem isn't the fan being dirty.. I noticed the weak air flow within a few days after I bought it.. I thought it would be a lot more efficient if there was more air volume.

Variable Resistor is a good idea but I'll probably end up using a butterfly valve in the duct work to adjust output as needed.
Doing it in this manor means I could also hook up a standard damper motor with a thermostat to sense stove temp and open or restrict the flow.

 

[Murphy2000]

I just noticed you mentioned running your stove on high. If your air is wide open the heat output will be limited. Maybe that's the issue here rather then the fan it's self.

Huh??? I don't understand.. The firebox has a maximum temperature.. Not sure exactly what that temperature is, and I'm not sure exactly when my fire is hot enough to meet that temperature exactly, but I do know when its hot enough that I don't want it to get any hotter. At that that time, the air coming out of the vent is hot hot hot! and I think it would be much more efficient if the air flow was doubled or tripled to lower the discharge temp and scrub more heat faster.

So far, I haven't heard any warning bells.. I think I'm going to give it a good this summer.. should be interesting...