Lowering Heating Costs by Closing Vents

[kuma]

I know - basic question - I just want to be careful and not overheat anything in the furnace. I have a 80K furnace (72K w/propane) and I want to reduce the heating bill - propane is expensive in Cali, $2 a gallon!! The fan speed is set at factory default which is 1350 cfm's - how many registers, measured in cfm's, do I need to leave open without overheating the furnace?

When I say registers in CFM's - I mean a 6 inch register is ~90 cfms, a 7" ~130 cfms... Right now I have a combination of 6" and 7" registers opened which total to about 900cfm's. I hope that makes sense... and I hope that enough airflow is crossing the heat exchanger as to not damage it...?

Thanks!

[totaleclipse]

It is best to not close any of your vents. When you do that, you not only decrease air flow as you mentioned, but you can also increase duct leakage, then you are trying to heat the world. It is best to not close any of the vents, and if you are worried about air flow, hire a compitant contractor to come out and test the ESP(external static pressure) of the unit and compair to the manufactures recommendations.

[gasguy]

While it sounds good, closing off supply registers will not lower your heating costs. It will just make the furnace work harder and less efficiently, as well as decreasing comfort and increasing the likelyhood of damaging the furnace. Shutting off registers will create cold zones in the house that will affect the heated areas by increasing the heat loss of those spaces.

If you want to save money increase the insulation in the home, install more energy efficient windows, and decrease leakage around doors, windows etc. Then make sure the furnace and duct system are sized properly for your house using manual J and D calculations.

[TheDuke]

I agree with two posts above
bad idea to close any, think about it you have a high limit if you slow down air flow what will happen the heat exchanger will get hotter then the norm then what it will go off on high limit safety, flame out but blower will blow to cool down the heat exchanger, cool off then kick back on.
this can cause your ignitor to burn out early also do damage to your furnace.
yes you can adjust vents little to heat rooms but bad to close em.

[ks ftc]

The CFM is controlled by the duct static pressure not the blower motor wheel RPM. If you really wish to close vents. Test the static with all vents open.

Then check the engineering data for the blower, this will tell you CFM.

If the static is low, CFM is high, start closing vents until you get the correct static/CFM. The furnace will operate as designed.

Don't get you hopes up, 90+% of air distribution systems in residential applications are under-sized.

[soleowner]

I understand your situation. I agree with the other posts.

Your furnace most likely does not operate at 1350 during heat mode. The fan in an 80% furnace has two speeds. Low speed for heating and high speed for cooling or Fan on. Low speed CFM is around 890. If you furnace is actually operating in heat mode at 1350 then your furnace is too big.

I have a recommendation for added comfort and lower bills.

Look up a third party product call www.FANHANDLER.com.

This device helps with comfort by better managing the fan
speed automatically.


Questions:

1. Is the thermostat located close to the return air vent? The thermostat
should be centrally located in an open area away from heat sources or windows etc.
2. What is the make and model of the furnace?
3.Are your ducts air tight?
4. Do you have insulation in the attic? If yes, is it still good?
R30 is a good thickness.
5. Do you have air conditioning?

[allstar08]

I'm sure that everyone in here has given you way too much info. The only time I have seen closing vents save money is when a two stage furnace is used on a split level home, and all the vents for downstairs are closed. once again too much info. Keep your vents open and upgrade your insulation, windows, doors, and seal your ductwork.

[kuma]

Wow - lots of info! Thanks! I just finished remodeling house - several years later... Anyway, all new dual pain windows, R30 in attic, new ducting, new furnace/ac... thermostat located in central part of house - away from doors, windows and cold air return... The things I cant change that would help are the walls - made out of adobe (8" thick, not sure of R value - maybe R8 - 10?) And the floors are mostly tile on a slab foundation - look great, nice in summer, cool in winter though:) Have some throw rugs here and there to help... Alright, looks like "it is what it is".

[kuma]

Your furnace most likely does not operate at 1350 during heat mode. The fan in an 80% furnace has two speeds. Low speed for heating and high speed for cooling or Fan on. Low speed CFM is around 890. If you furnace is actually operating in heat mode at 1350 then your furnace is too big.



Its a 5 ton AC so for cool it blows ~2000 cfm.s The default heat wiring motor speed is ~1350 cfms. Again its a 80K (72K using propane), 80% furnace - sounds like you think the motor speed needs to be increased for the furnace? It can be increased in heat mode to ~1700 cfms easily? If it should be increased then I definitely need to keep all vents open!

Thanks!

[heatermanbob]

I went on a call to an elderly womans home and found all of her vents closed except two in the living room. The heat exchanger cells on the 6 year old carrier were all cracked and seperated. she thought she was saving money by only heating the room she occupied:eek:

[soleowner]

Check out that "fan handler". More air flow most likely is not the answer.

Google "GE ECM variable speed motor".

John