Need more CFM from my pellet furnace

mbx5October 30, 2011

Just put in a St Croix SCF-050 unit... I have about 2k sq ft. Put it into my HVAC system, baffled out the heat pump.

What I am noticing so far - we can hold temp at 69-70 when 30deg outside...

I know this unit is big enough for my house size - but the one issue I have is flow....my hvac is pretty constricted. My air handler on my heat pump doesnt have any problem with it- but its prob 1.5x more flow... The St Croix is only 800cfm on high setting.

Is it feasible to put a larger CFM unit in there to get more flow? I don't think I will overcool the thing but I think I just need to get some more air pumping through there...

Any ideas?

Thanks

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christopher_55934

Exactly how is your system connected? Are you pulling return air from the return air grill of the HVAC system? If so what is the static pressure of the return side? What is the static pressure of the supply side. If it is constricted as you say these numbers should be high out of spec. If they are you need to open up the duct work to remove some of that restriction.

Minimum Duct Size
Round: 10"
Rectangular: 6" x 15"
Intake Air Duct should be 10% larger
Maximum Static Pressure: .4" Water Column
Velocity: 1400 FPM at the above mentioned duct sizes.

Attached a link for a duct fan, may work but it is a band-aid. The real fix is to open up the duct work. If your return air is not ducted I would get that hooked up also.

Here is a link that might be useful: Booster Fan

    Bookmark   October 30, 2011 at 9:20PM
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mbx5

Yes cold air return is ducted. Basically I am pulling out of the existing cold air return right out of the bottom of my heat pump, and blowing right into the upper plenum of the heat pump, and baffled the back side so it does not create a loop.

I am unsure of static pressure - its existing duct work in the house... The heat pump heats the place well...

I have an inline duct fan for one of my runs....the others I dont have access to any more because our basement was remodeled.

When the heat pump runs, the curtains blow when it kicks on....when the pellet furnace runs, can barely see them moving... It only has an 800cfm blower whereas the heat pump is around 1300....

    Bookmark   October 30, 2011 at 10:55PM
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mbx5

May have found the issue.. I am currently running in manual mode instead of thermostat mode. What a difference! I must have the wrong thermostat because I am at 74 and climbing a degree every 30-40 minutes. Its about 40deg outside right now...

Looks like this may work out afterall....although I still may go for more blower CFM to help distribute the heat better through some of the more restricted runs.

    Bookmark   November 2, 2011 at 12:09AM
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