More CFM?

[turbulator]

Running a St. Croix SCF-050.... max cfm on that blower is 800... My duct work in my house is constricted...not sure what the static pressure is, but its probably not ideal.... My heat pump has around 1500cfm... Wondering what your thoughts are on putting a larger blower on the St. Croix... I can get one from Grainger for a few hundred bucks....probably some minor mods to get it hooked up...would have to make sure the motor is the same hp and current load....

I am not necessarily looking for more BTU as I think the furnace is properly sized for my 2k sq ft..., I just want to distribute them better....

Thanks

 

[jtakeman]

I'd start with checking the vent temp where it comes out of the stove. If its really hot, Sure you can increase the CFM's. What is the CFM of the blower you plan to put in?

With increased CFM's you will move air accross the heat exchanger faster and it may not absorb the heat. You new vent temps will be lower, But yes the volume will be greater. You will turn the air over in the house quicker, But if the temp is too low. It may take longer to warm the rooms. You could comp this by running the furnace on a higher setting to increase the vent temps. But this will burn more fuel IMHO.

I doubled my blower CFM, But I had high temp readings where it exited the stove, I could afford to reduce the temps. The vent temp was actually hot enough to burn my toes on the floor registers. With the higher cfm's I lowered the temps to a more exceptable level.

 

[slangtruth]

I have a St. Croix Revolution which is very similar with a slightly higher (1000 cfm) blower fan. I've experimented with cycling the oil burner's fan to boost air speed but J's warning on the air moving too quickly through the heat exchangers to pick up the heat is well taken. Much more important is a good backdraft damper in the main furnace you have it hooked to, so heated air doesn't take the short circuit through the other furnace rather than actually going through the ducts and coming back through the return air like it's supposed to. The lower capacity fan means you're simply never going to feel hair-dryer air speed at the registers, but that is the right size for your heat output. I feed a total of five floor registers, four fed through an 8x12" metal trunk duct to 6" branches and one farther away on 6" flex, with the most remote ones being a good 15-20 feet from the furnace. I feel moving air if I hold my hand about 5" from the register, but it's nowhere near the velocity the king-size fan in the ancient oil burner develops.

 

[SmokeyTheBear]

In addition to what J is telling you about not moving the air too fast, you have to stay within the electrical capabilities of the controller on that unit, further if your duct work is truly constricted you can cause problems for the blower. The very last thing a blower needs is restriction on the output side, if you can measure the current flow of the blower it will go above its plate rating in a restricted output situation (which brings us back to what the controller can handle).

 

[turbulator]

Thanks for the info. Yea I have a baffle for backdraft....I have 8 rooms to blow heat into....large trunk line that breaks down into 6" flex toward the end... the farthest rooms don't get much flow at 800cfm....

I feel some heat coming out of my registers, but not really any moving air....only one I can feel significant air through is the downstairs bathroom with a feed directly off the main trunk line....

 

[SmokeyTheBear]

Thanks for the info. Yea I have a baffle for backdraft....I have 8 rooms to blow heat into....large trunk line that breaks down into 6" flex toward the end... the farthest rooms don't get much flow at 800cfm....

I feel some heat coming out of my registers, but not really any moving air....only one I can feel significant air through is the downstairs bathroom with a feed directly off the main trunk line....

If the joints aren't already taped and the ducting insulated, you may find a large difference by doing one or both.

 

[jtakeman]

Thanks for the info. Yea I have a baffle for backdraft....I have 8 rooms to blow heat into....large trunk line that breaks down into 6" flex toward the end... the farthest rooms don't get much flow at 800cfm....

I feel some heat coming out of my registers, but not really any moving air....only one I can feel significant air through is the downstairs bathroom with a feed directly off the main trunk line....

Check to see if you have some that have strong air flow. If you reduce these down a little the others will gain some flow. Very hard to balance the system out so that all the vents get equal air flow. Most registers have adjustments to reduce or even close them down. I'd try that first as its free.

Have you checked the vent temps yet?

Also do you have a closed loop system with a proper air return to the stove? Or are you just using the air in the basement?

Sorry for all the questions!

 

[jtakeman]

Thanks for the info. Yea I have a baffle for backdraft....I have 8 rooms to blow heat into....large trunk line that breaks down into 6" flex toward the end... the farthest rooms don't get much flow at 800cfm....

I feel some heat coming out of my registers, but not really any moving air....only one I can feel significant air through is the downstairs bathroom with a feed directly off the main trunk line....

If the joints aren't already taped and the ducting insulated, you may find a large difference by doing one or both.

I will vogue for this. Sealing the ducts inproves air flow to the registers and insulating them reduces the heat loss thru the ducting. Made a big diff in my system. No if I could only install a return air to it? I would only be heating the up stairs area. Basement temps would be even cooler! Cut the squarefootage I an heating in half!