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Hi, we replaced the A/C in our SW home last year. Went from I think a 1.5 or 2.0 ton unit to a 3.0 heat pump (we have about 1100 sf). Even with the increase sized unit, we are still not able to keep house cool enough. Especially the livingroom and kitchen areas. These rooms have higher ceiling and are in the center of home. In summer months the unit will run all day and in winter all night. Plus, have noticed mildew on two of the floor registers in home from condensation. Bought a humidity gauge and it reads from 53 - 63% throughout the day. Told hubby I feel we are loosing air underneath home and after checking we have concluded that yes we are cooling the crawlspace as well. Hubby said he will replace the current air ducts with a larger size air duct. Said the one with home is too small and not allowing proper air flow and thats possibly why we can't get home cool enough. However, he wants to run the new duct underneath the old and tie into where the floor registers are and close off the old duct. Said that if we pull out the old then we possible ruin the belly and its next to impossible to have the belly put back the way it was. Can you offer any advice and/or suggestions? Thanks!!

Hi,

Did you have a Manual J Load Calculation done to know correct size needed for home ? 3 tons may be too big.

Need a Manual D to know duct size needed.


IF you increase duct size, you'll need to upgrade the furnace blower motor.


You can replace duct like that, just be sure it is correct size and seal it up with mastic duct sealant.



Thanks,
Robert

Thank you for your help. No, don't think we had this calculation done. Is this something an HVAC person would do? Also, I don't know all about the construction of a mobile home but if we tie in the new duct to the old one, would we not be pushing the new duct through insulation and possibly have insulation in the new duct?

Hi,

Yes, an hvac tech should do it before sizing a system. Not sure how you're talking on tieing in the new duct.


You can run it below the old duct, no other way to do it.


Thanks,
Robert