OPs temp set point is 70. That’s why it’s so humid inside. It’s neither heating nor cooling. If he set point at 68 the humidity would be gone in 2 hours.

In fact based on his op, make set point 67 and let it pull all that moisture out over night.

Put the whole house in a bag of rice.

And a humidifier  installed on the system to add moisture.

Depends on a lot of things. I've definitely lived in houses where the AC wouldn't run enough to dry out the house no matter how low you set it.

True. But how about OP try it?  I’m not a Hvac guy, just amateur weather guy so Kaye and understanding of temp and dewpoint. My greatest invention will be a thermostat that lets you set dewpoint. But I think that needs a true wet bulb thermometer.

@amediocreshooter

Turn to cool mode, set point 67, fan auto. Record RH this evening, Report RH in the morning.

Outside air temp is about 58 tonight. Will running the AC at these temps damage the unit?

If it's 58 outside and thermostat is set to 67 I don't see your AC running much.

Get a dehumidifier and stop overthinking it.

We have a whole home unit (Aprilaire 1850) and it works well.

Your furnace is probably also not the right size.

A google search says most A/C unit are not designed to operate below 60F outside temp.

Just go buy a dehumidifer.  They are not expensive.

That’s the route I’m going. Will pick one up this week. Don’t want mildew forming.

A question from someone that has dry skin and as lived with the burden of <15% humidity for over 50yrs.... how in the hell does a dehumidifier work?

I’ve never heard of any such nonsense. But I’m not an Hvac pro. If it makes you feel better do it in the morning.

Record outside temp and dewpoint when you start. I struggled with exactly what you’re dealing with and why I bought such a fancy top of the line train multistage system. To control humidity. Otherwise I was managing humidity myself instead of the thermostat/system.

Its pretty much an air conditioner. Literally.

Some modern systems have variable speed compressors and variable speed blowers.  They can be set to adjust humidity by decreasing the cooling rate and increasing run time.  They idea is to run at long duration with the air going through the evaporator dropping just below the dew point to release moisture.

Another trick is to run the AC and heat to maintain humidity and temperature.  Some systems have a dehumidifier installed in the central system that runs to dehumidify both the evaporator and condenser are in the air flow so it warms the air back up after cooling.  The ac will come on if temperatures are too high.

In the typical home, contractors oversize the AC, so they don't run long enough to dehumidify the air in shoulder seasons where the AC doesn't run as much as in summer.  Those systems don't dehumidify the air and you can get quite high humidity levels in the shoulder seasons.

I made a thread about this in the summer. I basically live in a humidor.

It'd 59 degrees outside but 97% humidity.

Indoors we have gear set to 72 and it barely kicks on but 66% humidity.

This.  I think the one I had could remove something like 90 pints a day.  Best to have the type that is connected into the central air handler.  Also, need a pump to pump all that water down a drain.  Drip systems tend to plug up with biologicals.

This will work.  However, in the typical oversized system, you will end up with the house cooling.  Then you have to run the heater.  This will really dry the air out.

I had to do this in the shoulder seasons.  Sort of a pain in the ass and it's and inconsistent way to control humidity since you have to manually do it.

Better to retrofit a whole house dehumidifier like Santa Fe.

Gulf Coast states don't have basements and they have extreme humidity conditions.  The shoulder seasons can last multiple weeks.

It's a smaller AC unit where both the evaporator and condenser are inside.  It pulls in air and cools it to the dew point at the evaporator than runs the cooled air over the condenser to warm it back up. (At least the better ones like Santa Fe work that way) Net result is slightly warmer air is discharged than sucked in.  Air is much dryer as it was cooled below dew point to drop moisture and the heating further reduces relative humidity.

Where's the humidity coming from?

I do HVAC controls and deal with this constantly.

You never want to oversize your HVAC system in cooling. Cooling is what dehumidifies the air. It drops the coil temperature below dewpoint to get the moisture out of the air. It needs run time to cycle the air through the unit. In commercial settings you have a reheat coil that reheats the air leaving the coil to prevent you from overcooling the space.

Humidity is a very poor control variable. It fluctuates too much with room temperature changes. I care more about the dewpoint.

Some houses now are so tight the AC doesn't run much anyway. So, they install ERV units to get ventilation but also keep humidity in check.

I just turn the A/C on and run it. I may not want the house at 68 degrees but in less than an hour, maybe  20 minutes the humidity will drop significantly. Then I turn the heat pump to heat and back to 72 degrees, now it's good for a day or so.

Have a good exhaust fan in any bathroom and run it while in the shower and maybe 1 hour afterwards to remove all the moisture.

So stick thing in a spare room or the living room.  People with basements usually just put them down there because it's a humid place and they don't have to listen to them, but having a basement is not a requirement for using a dehumidifier.

You could.  But we have so much humidity and our shoulder seasons can be long that the cheap portable room units are usually not that great of a solution.  The central units are better.

I just googled "Texas weather" and "Indiana weather".  I understand states are large and this does not mean your living room but here is what it said:

Texas today: 37%

Indiana today: 87%

IN averages 9% more humid than Texas throughout the year.

No PV yet, but I will.

Gas stove, dryer, and NG tankless water heater. The air handler is hydronic.

I also have a 12,000BTU high wall minisplit and and a HPWH. Since installing the mini-split and HPWH as well as improving the envelope, I have not needed to use the dehumidifier, which was absolutely necessary with the 36,000BTU single stage 1997-timeframe central AC unit. Not only did my energy use (and bill) decrease, the house is more comfortable as well.

With the addition of a PV set-up in the future, I'll be able to lean more heavily on electric.

@HIMARS13A

Crazy that you reduced the size of your cooling system by 70% and it still works.

By hydronic you mean you have a tankless water heater/boiler that pumps hot water through a coil for forced air heating?

That seems like extra steps.

West Texas is a desert.  Gulf Coast Texas is a swamp.

Exactly what I did. My basement is now very tolerable.

I have a aprilaire unit hooked up to its own duct work.
It maintains whatever humidity you set it on.
Tried hooking up to the central duct work and it did
not work to well. Has to have its own duct work.

First installed it took a week to get the humidity under control.
Everything holds moisture and takes time to remove, not running
your A/C for two hrs like some nut here said would work.

That's an absurd statement. Texas is 870 miles across and has An extremely ling Gulf Coast. It has deserts in the west and swamps and marshes in the east.

Speaking of a humidity if Texas is therefore nonsensical. Especially when it was specifically pointed out that I was talking about the Gulf Coast of Texas and Houston should be known by anyone as being near the Gulf Coast.

In any case, Houston at Intercontinental Airport which is at the northern end of Houston and further away from Galveston Bay is more Humid year round than Jeffersonville Indiana as an example.

Our winters are mild and the transition from summer to not-really fall winter and spring is gradual. So the shoulder seasons where neither the heater or AC run long periods of time are long and dehumidification is a problem.

Our houses are built slab on grade. Moisture in many homes comes up through the slab. Our soil is typically clay and drainage is slow. Our water tables are high. So high we have crawfish, including our own species, the Houston crawfish, that live in the clay soils in our yards. They make roll up the clay with their tails into clay balls and stack the balls at the mouth of their yard tunnels forming little clay ball chimneys that can later harden in the sun and become a nuisance when mowing.

We live on a giant clay sponge full of crawfish.

Indiana has no idea what real humidity is.

You can literally find average RH on the internet. Texas is not nearly as humid as people think.

Even the Gulf Coast is about on par with Indiana.

So if you think the gulf coast is a swamp, then all of IN is a swamp.

If your dehumidifier doesn’t have a pump you can rig up a fountain pump on a timer & some tubing or use an automatic digital plant waterer to route the water to a drain or sink. Don’t have to empty the tank they way.

The plant waterer is pretty much a pump and a timer.

You can google, but you have to understand what you are googling.  Cooler air holds less moisture.  Warmer air holds more moisture.  The Texas Gulf Coast is much warmer on an annual basis than Indiana.  That means, that even if the annual outdoor relative humidity were the same, the absolute humidity and dew point are much higher in the Texas Gulf Coast.  That means that when we cool our air to a comfortable temperature in our homes, a much larger amount of water must be removed to get to an acceptable RH.

It's not even close on an annual basis or in July or in January.  Our dew point is so high, we have fog horns.  Two ships collided right off my backyard on Galveston Bay.  The fog was so dense, I couldn't see the bay at all.

In January, the dew point in all parts of Indiana is less than 30 deg F. and that's only at the Ohio River, the rest of the state has a dew point less than 20 deg f.
When you heat that air to 65, your RH will drop to low enough levels that some people use humidifiers.

During our shoulder seasons in October, November and even sometimes December, the temperature of our homes can hover at the dew point.  The AC doesn't run long enough to drop all that moisture out of the air.  Every time the door is opened, more very wet air moves in.  All that moisture means our indoor RH can be much harder to control during the shoulder seasons.
.
Since the total volume of water in our air is much higher than places like Indiana, those little plug in dehumidifers you get are often not enough.  They simply can't remove enough moisture to lower the RH to acceptable levels.

There are much more efficient and larger capacity dehumidifiers that are up to the job for coastal dehumidification.  A competent HVAC company can provide specific guidance way more advanced than some guy who thinks Indiana has humidity that approaches Gulf Coast levels of humidity.

https://www.santa-fe-products.com/product/ultra120v-dehumidifier/

I understand what you're saying. I'm doing a retrofit as opposed to new construction and I didn't understand much of what I do now. It has definitely been a learning process and I would do it differently if I was doing a new build. For now, my heat loss is still too great to depend on electric (even with the increased efficiency of a heat pump) for heat. I replaced an older 80% efficient furnace, the natural draft gas water heater, and the AC system at the same time.

I would like to add more exterior insulation, and new windows/siding, as well as a PV set-up over the next two years. With what I've learned, I'm trying to figure out the right balance of added exterior insulation vs. increased number of PV panels. To do so, I'm thinking I may install a PV set-up approximately 1/4 the size I think I will need to see the real world results and scale it up as I need.

I will say that one of the things I learned was how much an even marginally better envelope could actually save money when it came to the mechanical system sizing and equipment choices. Like you pointed out, I may not need the central hydronic heat/tankless system, and could have gotten away with a ducted inverter-driven heat pump with a med/high static air-handler if I had added more insulation and the PV panels earlier. When I was originally planning it, I was concerned with redundancy, but I could have had redundancy with electric supplied by the grid and a PV set-up as well.

The hydronic heat system is an engineered Bosch system. It looks sort of like this:

Attached File

I get it. Without the right envelope electric heating doesn't work so good.



The guys I know doing cold weather retrofits are doing air sealing and insulation the installing 2-3 ton variable heat pumps with heat strips for dehumidification and extreme colt.

It's $20,000 to $40,000 per house. But very comfortable.

Just wanted to update this thread.

I bought the above. It was about $300 with tax and shipping. It’s working fantastic. It’s not terribly loud, and connects via wifi so I can shut it off or turn it on remotely. It also shuts off automatically when the desired humidity is reached.

I havent seen numbers below 65% inside since spring when it’s extremely dry and doesn’t rain for weeks. It is currently <43% everywhere I measure in the house. There is a noticeable improvement in feel and smell in many areas of the house (like closets). When putting on dress shirts they always felt somewhat clammy but now everything is very dry.

I have the same problem in my main bathroom closet.  We heat exclusively with a wood stove, so our main bathroom loads up with humidity from taking showers etc and no central heat on.  I solved the problem with a 70 pint dehumidifier from HD.  Had it 7 years now; dry as a bone back in the closet.