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certain vents blowing cold air

I have a new (<2 yrs old) house with forced air, propane fueled heating; there are 2 heating/cooling zones - 1 for downstairs and the other zone for upstairs. On the ground floor most of the vents put out warm air. However, 3 vents blow only cold air --- any comments or suggestions?

Re: certain vents blowing cold air

Have you checked to see that all the supply & return registers are open.

have you checked to see if any motor-driven duct dampers are closed.

Have you changed the furnace filter recently?

Have you checked for duct leaks & made the repair with sheet metal screws or mastic, or other approved methods.

Have you felt the plenum and the ducting runs to see if they are hot or as least warm.

Have you checked the flame inside the furnace to see if it is normal height---that all the burners are lit, & the flame is blue???

Re: certain vents blowing cold air

I agree with DB about leaks in the ducting.

The further the run to those rooms the greater the chance of heat loss because of improperly sized and/or leaky ducts.

The point about reducing the fan speed I don't agree with .... that will upset the balance of the system.

You shouldn't have to close off vents or adjust dampers if the system is properly done ..... especially being such a new home.

You might consider having a HVAC company come out to evaluate the situation and check the balance system .... especially since there are zone dampers involved.

Just 2 cents worth.:)

Re: certain vents blowing cold air

If it was not set up properly an incorrect fan/blower speed can effect the performance of the system.

Yep ... totally agree with you ... DB. :)

This can be a common occurrence when it comes to new homes .... especially ones that are part of a new housing development . When a builder has multiple units they contract out the sub trades for the cheapest pricing. Generally the trades are paid per house and it's not uncommon for those trades to quickly do their work and move on to the next one. Many times things aren't done as well as they should be because of short cuts.

When it comes to HVAC there can be situations where the installation is quickly done without the attention needed for proper sealing and some cases proper sizing of the duct work ..... which show up as 10 - 20 % air flow loss issues within the home.

There are times when the home was first designed the HVAC equipment may have been sized accordingly but during construction changes were made .... such as adding more windows in the South or West sides of the home adding more heat loss /gain loads. When this happens there are times the HVAC equipment is not revised to accommodate these heat loss /gain loads.

After these systems are installed in new housing developments they may not be checked and adjusted for the balance ..... another short cut.

A reputable HVAC company can test and evaluate the HVAC system in the home and properly check and balance the system. They will use special instruments to measure the CFM air flow as well as the actual temperature coming out of each vent to tell if it's correct. If they find irregularities they would be able to determine what may need correcting.

Hope this helps. :)

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