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Message
re: Humidity Level New Construction
Posted on 7/27/22 at 9:45 am to notsince98
Posted on 7/27/22 at 9:45 am to notsince98
quote:
You should not be changing wiring on the blower motor. The blower speeds are adjusted by dipswitches located on the furnace control board.
I have a PSC blower which does not have the dip switches. ECM blowers usually have them I believe.
2
Posted on 7/27/22 at 10:12 am to Snow
quote:
I’m curious about the cfm/ton setting. I’ll have to research that unless someone wants to elaborate.
To briefly elaborate, the recommend cfm per ton of HVAC for much of the country is 400 CFM per ton. However, in humid areas of the country, aka S LA, the general recommendation is to slow the blower speed to deliver 350 CFM per ton so that warmer humid conditioned air is in longer contact with the cold evaporator coil to increase latent heat (=humidity) removal. In hot dry areas, e.g., SW USA, with low latent heat (humidity) the recommendation is to increase blower fan speed to about 450 cfm ton.
Air handler/furnace blower speed setting for cooling are typically set to the highest speed at the factory by default, and it is the installing HVAC tech’s job to adjust the speed as appropriate for a region or an individual house, this is not always done.
As you learned for a single stage HVAC system, adjusting blower fan speed to a lower setting, is as simple as swapping out a blower motor fan wire or adjusting a dip switch on the control board in the air handler.
Reducing HVAC blower fan speed is the easiest thing try first when a house is dealing with excessively high humidity. (ETA: assuming it is set to the highest fan speed to begin with).
Notsince98 listed others factors that can contribute to excessively high humidity in a house. I’ll add another - if the air handler/furnace is in the attic (which most are in our area) a significant leak in the return air duct(s) in the attic, which is under negative pressure, will draw excessively hot, moisture laden air from the attic into the air handler that the evaporator coil may not be able to adequately remove increasing humidity in the house. In your case, you said HVAC techs checked your ductwork and ruled that out.
Good job on your part figuring out to adjust the air handler/furnace blower speed on your own.
This post was edited on 7/29/22 at 9:19 am
Posted on 7/27/22 at 10:35 am to Snow
quote:
I have a PSC blower which does not have the dip switches. ECM blowers usually have them I believe.
It depends on the control board used in the air handler, some PSC blower motors might be connected to control boards that have dip switches to adjust blower fan speed without having to move blower motor wires. But mine (PSC blower motor), like yours, requires physically disconnecting and reattaching the appropriate colored blower motor wire to a spade connector on the control board to adjust fan speed to an appropriate CFM output.
Good video explaining this LINK - this HVAC tech (New Jersey) has a great HVAC YouTube channel.
This post was edited on 7/27/22 at 11:12 am
Posted on 7/27/22 at 10:39 am to Snow
quote:
I have a PSC blower which does not have the dip switches. ECM blowers usually have them I believe.
Interesting. My only first hand experience with PSC blower is on my parents Carrier furnace and it has dip switches for speed settings.
Posted on 7/27/22 at 10:57 am to notsince98
quote:
nteresting. My only first hand experience with PSC blower is on my parents Carrier furnace and it has dip switches for speed settings.
I will double check it, but I didn’t see any other adjustments.
Crawdad, notsince98. Thanks again for all the info and guidance! I’m still blown away that it took me this long to figure this one out.
Crawdad, thanks for the explanation. That helped me tie it all together. I’ll let you know how it goes.
Humidity was at 55% this morning and it hasn’t been that low since before summer. Looking like it’s going the right direction. Hell yeah!!
Posted on 7/27/22 at 11:09 am to notsince98
quote:
Interesting. My only first hand experience with PSC blower is on my parents Carrier furnace and it has dip switches for speed settings.
This the OEM control board on my air handler/furnace. No dip switches to control blower motor fan speed.
But if the board failed and needed to be replaced, this is the OEM replacement board which has dip switches to control blower fan speed.
This post was edited on 7/27/22 at 11:16 am
Posted on 7/27/22 at 11:31 am to CrawDude
Yeah, I looked up the Rheem furnace and it definitely doesnt have dip switches.
Posted on 7/27/22 at 1:57 pm to redstick13
quote:
I’m guessing neither of these homes had Sheetrock.
They both had been sheetrocked sat some point. My parents house south of Houston was built in the early 1960s, was no different. Rock wool insulation in the attic, single pane windows, no insulation in the walls, and Sheetrock throughout. There were millions of houses built like this in the 60s, but have not heard of mold being a issue in them today.
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