HVAC Gurus

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How much would it cost to add in-line dehumidification to an existing HVAC unit? It would go on my first floor system, approx 1800sq.ft(non-baller). My house is too "tight" to keep the humidity down where I want it.

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Have a competent HVAC engineer or professional (not just an installer) come out and look at the system. There are all kinds of possible reasons why that system can't maintain humidity levels where you'd like them. Too many to say "it'll cost you about tree-fiddy". It could be as simple as adding a humidistat into the control loop with a possible reheat coil. It could be to install a different evaporating or condensing unit. It could involve a 100% Dedicated Outside Air System. Each of those options gets progressively more expensive, but each also responds to increasingly difficult and serious root causes. Those aren't even all of the possible solutions that can be brought to bear on a humidity issue. Without knowing WHY you're seeing excess humidity inside the building's envelope, you can't effectively fix the issue.

Unfortunately, HVAC/R can be pretty complex, but the economics of the thing mean that we have to try to use one-size-fits all solutions and use rules of thumb to specify equipment for home use. Sometimes those cheaper plug-and-play options that are cost effective when you look at it in the aggregate just don't work well for every home and it can start getting pricier to bring the kind of expertise and hardware that can solve the problem into play.

I suspect you'll find that you won't need anything as drastic or expensive as a DOAS. Still, it'll be worth it to spend some money to hire someone who can fix it properly the first time than to try to cheap out and hire someone that will throw various solutions at it until one works.

Thanks for the reply. I had a feeling it wouldn't be so simple, but I appreciate the action plan. FWIW the humidity in my house stays 48-55%. That is with the air on 74 during the day and 71 at night.

Seems that a tight house would be easier to keep the humidity at a lower level. The humidity is outside and if you are not letting it in, you have something else going on besides a tight house.

Out of curiosity, what is your indoor humidity?

Unit maybe oversized and not running enough.

Something is creating excessive moisture from inside the house. Stove vent not venting to the outside or not using vent fans while showering.

Maybe an air leak on the return air side and it is sucking in attic air.

Air handler speed may be running too high causing the unit to not be able to remove enough moisture.

48-55 isn't really a bad zone to stay in. There are many factors that could raise or lower it though.

i.e. it will go up after rainshowers. Is that during the middle of the day when no one's home or at night when outdoor tems are lower?

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$297 on Amazon

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With tax about...