Assuming that Manual J is correct (and based on your complaint) you need more cooling. Going the route of new central zoned unit, duct work changes etc. is the expensive fix especially with a relatively new unit already in place. By just buying a mini split heat pump and minor duct modifications you should be able to isolate the bonus room with the mini split and let the air that was going to that room be redistributed to the other rooms. Bonus room is 216 s.f. Not knowing the number of windows or orientation of the bonus room among other things makes it harder to recommend mini split size but as mini splits can "throttle down" the compressor and air flow it's less of a problem if you over sized the unit...I live in Columbia, SC so I'm familiar with the climate. I have a 15,000 btu (1.25 tons) mini split heat pump in my 400 s.f. glassed in sun porch (east orientation so the heating load isn't as much) which does a nice job handling heating and cooling. Even with a south/west orientation I'd think that 21,000 btu might be more than you need for your bonus room.

Great units, for certain. Is this for one unit or two? Have you considered the possibility of insulating your hot water pipes and putting in ONE large hot water heater? This would reduce your standby loss (depending on your run length of your pipes). How about a tankless hot water heater? They use way less gas and they are so much easier to install now rather than later. If this is a two story home, you want to make absolutely certain of the following: You need either: (1) a zoned system with two different units. (2) one system with automatically controlled zones. (Carrier Infinity is known to be among the best with their zoned system and the price would be slightly less than for two systems--IF you do it now rather than later--drywall labor etc). Don't let anyone tell you that one unit can heat and cool a two story home. It needs to be zoned: either with one unit and thermostatically controlled dampers or two units. Don't take my word for it. Talk to any 2 story homeowner that has one unit for two floors. Too, I would seriously consider adding HVAC to the basement (especially if you ever plan on finishing the basement) Running the ductwork would only be a matter of a thousand bucks or two. Doing it now is a whole lot less expensive than later. Generally, the air conditioning and heating needs of a basement aren't all that significant and you can often use the same size unit depending on the outdoor exposure of your walls and windows/insulation etc. Another thing you may want to consider is having your ducts SEALED with a company that specializes in this. It is not uncommon to have brand new ductwork that LEAKS 20% of your system capacity. It is virtually impossible to get your ducts good and tight without this method. Aeroseal is a proven method which blows little particles into the "holes" and permanently seals them from the inside. Typical cost for this size home: perhaps $500-$750. They print the before and after results for you right then and there. It only takes an hour or two. Cold winters are no problem IF these unit(s) are correctly installed according to the heat load/heat loss of your home. On a twenty thousand dollar job, the HVAC contractor can take an hour or two and run a load for you. Insist on it. Before you go with American Standard/Trane (which are excellent units), check out the Carrier Infinity system with zoning. (You can have up to EIGHT individually controlled zones) Many professionals and homeowners testify that the Infinity system is the best. I should know as I have two of them! Good luck!

I'd be more than happy to help you but your model number is incorrect. I think you mean a B1HH048 and your missing a number from the serial number. I think the unit was made in middle of January 1998... from what i can tell.

ionized, There is no need to run a humidifier to "supply latent heat." as I stated, the amount of heat removed from the room is very small... it will not have a measurable effect on either temperature or humidity in a basement, for example. In an earlier thread on this subject I provided some numbers. My heat pump hot water heater (during the summer) removes maybe a liter of condensate from my basement per day... there has never been an observed change in temperature, or humidity for that matter. In the extreme case where no hot water is used, the amount of heat removed from the room ambient is a net of ZERO as the heated tank water's heat is lost back into the room. If I lived in northern Maine with no Natural Gas available I would not hesitate to have a heat pump hot water heater. As I said, I'm saving $45-50 every month for hot water for two adults in MD. Parenthetically, I would point out that the hybrid hot water heater is not going to measurably contribute to home cooling during the summer.