I am going to agree with previous posters on several accounts: 1. Depending on where you live and how much annual precipitation your area receives, you may not need a humidifier. 2. Live in the house a little before you purchase a humidifier. This is a good idea for a couple of reasons, one of which is you will want to establish some kind of baseline by buying one of those little digital indoor climate readers that gives you humidity and temperature readings so you know what you're dealing with, and only then will you know the size of dehumidifier (or number of dehumidifiers) you'll need. 3. If you NEED a dehumidifier, do not go too cheap or too small. Read lots of online reviews and make sure you get the right size with the right drainage options. If you're not using the basement frequently (i.e., not planning to check on the unit several times a day during spring rainy season or the humid days of summer) and live in an area with a long summer + high humidity, you may need a larger unit with built-in pump options and a hose attachment that drains to a sink/sump pump. Too big and powerful with infrequently used pump and outlet hose options is better than too small with no pump and no hose options that you have to remember to dump every 3 hours to keep the humidity down to 70% (which is, BTW, waaay too high for most basements). You will end up spending a lot more in the end if you have to deal with mold/moisture remediation.

I guess adding the basement wouldn't shorten the cycle, but it would lengthen the time between cycles. A/C is set at 75, and basement is 69. Blending bsmt air with living space upstairs would cool upstairs even without any a/c on, if I didn't mind the extra humidity and radon. The only difference, as I understand it, between an air conditioner and a dehumidifier is that the heat from the a/c condenser can be separately vented if desired. An a/c's dehumidification should equal a dehumidifier's, just as an a/c cools as well as a heat pump - all the same machine, except how the plumbing and venting is arranged. The only other considerations are that if it is vented, the a/c will cool the bsmt, as well as drawing in moist outside air, both increasing RH. In other words, the dehumidifier (or a/c in unvented dehumidifier mode) achieves part of its dehumidification by heating the space, or at least by not cooling it. I think if the a/c unit can operate at temps in the 60s, it is preferred, as it has the flexibility of running in cooling mode (vented) or dehumidifier mode (unvented). I'm also thinking it might be more efficient, as EER is reported (even tho not great), while there's not much reason for dehumidifier mfr to make unit efficient.

Your welcome, gooddog. You can't vent the heat and keep the dry air. You may want to try raising the humidity level. Hot and humid is unlikely in a basement. If you want to vent the utility room to the apartment, there are several choices. I just leave the utility room door open and blow the dehumidifier exhaust out the door. All other ways, done right, probably cost more money than buying an additional dehumidifier. The least expensive way to dehumidify the other part of your basement with a closed utility room is to add another dehumidifier. If that setup is unacceptable, the next choice is to vent your utility room into the larger part of the basement. This needs circulation both in and out of the utility room . If you have non-electric furnace or water heater in your utility room, you must ventilate in a way that does not cause negative pressure in that space (you can't just add one exhaust fan). If you have gas/oil burning appliances in the basement, you hopefully already have one or two carbon monoxide detectors on that level. The air needs to move both in and out a low at low volume. I'm assuming that the your utility room and the basement apartment share a common wall. First, I would investigate controlling the whole setup with a line voltage humidistat like the Honeywell H46C 1166. This device simply turns power on and off to humidifier and ventilation fans based on humidity. The honeywell would be placed in the apartment on the common wall. I haven't used this humidistat, but based on specs it would be my starting point. Most/all dehumidifiers save their setting during power failure. This allows these devices to be remotely controlled by simply cutting power. I'm assuming your dehumidifier has a continuous operation setting, and this setting is saved when power is cut. The choice for ventilation is one fan and a large vent, or two small fans running in opposite directions. The vent option would let more noise into the apartment. SInce these fans would run many hours per year, the most expensive fans provide the best economics. Panasonic 70 cfm through the wall fans are ~$170 each and very quite. The only issue is needing a finished looking vent cover on both sides. You could also investigate less expensive Suncourt products. People with wood stoves use these types of products to circulate air to adjoining rooms. You may think "spending this money, why not put in a whole house system in the ductwork". Expense aside, the problem with a whole house ducted system is dehumidifying the basement with the windows open upstairs. Running a central dehumidifier with the windows open is attempting to dehumidify the world. In a houses with basement humidity problems, the lower level needs its own system. In new construction a damper system could be installed in the main ductwork to only dehumidify the basement when the AC if off. But in new construction the correct approach is to adequately dampproof the outside of the foundation wall so that no special basement dehumidification is needed. It is worth listening to an HVAC company for their proposed solution based on your specific house, ductwork and climate. If running a second dehumidifier in the apartment is acceptable part of the day, an appliance timer could be used. Or an occupancy sensor could be used in a space to only run a dehumidifier when the space is empty.

I know nothing about why your home is not set up for central air. I can speak knowledgeably about split a/c units. We installed them when we lived in Thailand. They are remarkable, in that they usually feature a dehumidify setting, to get the moisture out without making it too cold, as well as a cooling setting. If they worked at 17 degrees from the equator during monsoon season and hot dry season they ought to work well in Washington state. We went with small units in each bedroom, so that we were only cooling the area we were in, and one larger 20kbtu unit for the entire downstairs.