jbaker what is your fuel source for your hydro system? if you are satisfied with the operating cost and comfort of the hydro system, I see no reason to add a furnace. I would prefer that the air handler be located in a basement utility room over an attic location. If you are going with one system for all three levels, then I would want zoning controls for the three different zones. And if you decide to go zoning controls, then Bryant Evolution or Carrier Infinity is the way to go. They have the best single cource residential integrated control on the market. And you could consider a high eff heat pump system over straight AC especially taking into consideration your location/climate. I would get a couple of quotes. you need more returns on top and main floors for best airflow and overall comfort. ask quoting dealers for recommendations. finished basements at or partially below grade with reasonable insulation qualities have relatively low cooling and heating loads. IMO Good Luck!

There's too much information that has to be known to be able to give a reasonable estimate without a site survey. The area of the country also plays a big part on what you can expect to be a competitive cost for repairs/installations. Are you in a high rise condo where the A/C company may have to rent or hire a rig to hoist the equipment? In my area, markup is 300 percent of actual cost (cost of equipment, cost of labor, cost of sales)even though I personally have never charged that much, it helps determine if our prices are competitive and integrity is maintained. Too low a price can trigger a negative (and usually justifiable) perception of a company too. Depending on how busy the shop is, availability of other companies within the area (supply and demand) and whether the company even wants to do the job makes a difference on the cost of a job. Many times, if a company wants to specialize in commercial work, they will estimate a very high cost on residential work hoping you will try elsewhere and if you don't, it makes it worth their while to do the work. Also, what types of guarantee, value added incentives does the company offer? Nothing is free so "throw in's" are still included in the overall cost. Some companies don't even want to service units they did not clean install and will charge high prices for service and replacement. I'll attempt to give you some idea of cost, at the risk of TIGER shaking his head in disgust, and I do highly respect his opinions and AGREE with his opinion here (even though he is in Texas and I'm in Maryland). You should try to get 3 people to come out, survey the situation and and give a solid estimate. I know with this current heat wave, folks don't want to wait and just go with what ever is presented to them and get the "oh no's" later, just to alleviate the suffering. Your pocket book and risk management will determine which way you might go. For example, the prices may be high in your area and full replacement now, might justify the costs (and rising costs)of future repair work. Getting at least 3 estimates with site surveys can help you make the best decision. For example, if your condo is ground level and the unit was properly sized, and it doesn't require the tech to try to do jumping jacks in a phone booth, I could give you 3 estimates. Fix the hole, check for leaks, replace the filter dryer, vacuum and recharge the system for around $600.00. Just patching isn't all that would have to be done. The tech would have to assure the unit is at it's optimum before he left so coil cleaning, airflow adjustments, etc would need to be done to assure a satisfied customer. I'd guarantee my patch for a year but caution you another leak could appear elsewhere, something else could go wrong and due to the age of your unit, there would be no cost or part coverage from the manufacturer or supplier. I could plop a matched/exact condensing unit in for about $1,500.00-$2000.00. Again, the guarantee would be that which is provided by the manufacturer, cautioning you that any failures on the part of anything existing on the current unit that remain, that causes damage to the new condensing unit because of failue, will not be covered and could void guarantees and warranties on the new unit. Then there is complete replacement. Assuming all the manual conditions match what you have and, the manufacturer, model, seer that is being installed (in other words, mostly plug and play), that sized unit could cost approximately 5-8 thousand. Other companies in the area would charge much more, others would beat my estimate by a few dollars hoping to get the job. Obviously reputation and reliability in the area plays a big part. I have been known to hire a competitor to do certain jobs just to maintain my reliability reputation. That competitor luckily is one I trained and helped get into business so, that does help. More info than you might have wanted but even a little knowledge will help you feel better about whatever decision you make. Good luck!!!

Not a PRO, but I believe that TDR stands for time delay relay, which might affect fan operation. To expand on what Tiger said, different brands of modulating furnaces behave differently with regard to staging (heat levels). Speaking as a Rheem (mod) owner, the thermostat 'knows' what the set point is, but also, the indoor temp. So, let's say, that on recovering from a setback, knowing how many degrees it needs to heat, it will start out at as high a level as it needs to in order to heat things up. As the home approaches set point, its heat loss lessen, and thus the heat input will progressively modulate LOWER. Throughout the day, responding to indoor or outdoor conditions, the stat will respond by directing the heat input higher or lower (without regard to previous cycles). So leaving the doors/windows open, or running multiple ovens will elicit response (up or down) at any time. Other brands may differ in their response. They will start out at a given rate (some based on previous cycles) and ramp up over time until the stat is satisfied. Not good for a large setback. They may not have the ability to ramp down during the same cycle. Thus the up/down scheme. Without being specific as to brand, your mileage may vary. V

Wow! You've all given me a lot to think about. Thanks! Ionized--my fuel source is electricity. Very few people use any kind of gas out here because it's a lot more expensive. After rewiring the house and doing whatever I decide to do with HVAC, my next project will be a wood burning stove. I hope for it to be our (my adult daughter lives with me) primary heat source, as well as our emergency backup for power outages. It will be another expensive upgrade, as I have to use a stove specifically approved for use in a mobile home, and it must be installed by a certified licensed contractor. A county inspection has to be done at the half way installation point and at the end. Don't get me wrong--I'm very glad these safety regs are in place! It just makes it expensive. Oh, and ducts are mostly inside, but in a manufactured home they have to get to them from under the house, as I understand it. That means crawling under the house, which is no fun. I hear you telling me maintenance is required and I will make sure that's done on a regular basis. Klemperer, thanks for the reassurance. I'm not sure if we'll have to move out for HVAC install--I know we will for the rewiring. As you probably know, these old mobile homes were wired with cheap aluminum wiring that isn't even legal anymore. Even if the system wasn't failing, I'd still rewire just for safety. It's wired for 100 amps; I'm thinking I should upgrade to 200 amps, to meet the demands of a future kitchen remodel and our modern electronics. Thoughts? SnidelyWhiplash--Love the name! Fond memories of watching of watching cartoons--Wacky Races!-- with my brothers back in the day! You are right--I'm dumping a lot of $$ into a 37 year old manufactured home. But I have my reasons. I cannot qualify for a conventional home loan, and I hate debt of any kind. I decided to buy an old manufactured home from a close friend for cash. I'm refurbishing it subfloor to roof. Without going into a huge long story, I'm an academic researcher and I have a research grant (private, not government) whereby I get a chunk of money three times a year that I can use however I want. I've designated $6,000 each trimester for home refurbishing, and the rest I live on. The home will never be worth what I'm putting into it, but at the end of the day, I'll have a well-built, comfortable home that I own outright. I will live here the rest of my life, Lord willing and the creek don't rise, and then it will go to my daughter. So ROI is not a concern for me. Money, however, is, so I want to do the smart thing financially. homepro01-- I agree. I'm sure the window unit in the LR is not well sealed. Luckily, we don't have a mosquito problem here, and really not many bugs. However, it certainly is insecure in terms of an access point for bad guys. At the moment, the unsealedness, if I may make up my own word, is the least problematic of my insulation concerns, but I'm going to buff up the insulation substantially when I put in new flooring, siding, and roof. Nevertheless, it is a point well taken. Thanks. HVAC consulting--Thanks. I know I can get a mini split that does heat (heat pump), a/c, and dehumidifying, although as one poster mentioned, humidity is not a big issue in my neck of the woods. I hear what you're saying--how "big" I want to go will affect what other choices I make, and of course, my costs. And you are so right about mobile/manufactured homes--there are differences that must be taken into consideration. Based on everything you all have said, I think it would be prudent to get estimates for both central heat/air and the mini-split, which all things being equal I think I'm leaning towards. Since I will have to replace the furnace and the window a/c within a couple of years anyway, I think it makes sense to do it all in one shot. Once again I thank all of you so much for taking time out of your busy schedules to answer my questions! :-) I truly appreciate it. If anyone's interested, once I get estimates and make a decision, I'll let you know what's happening! Thanks! Have a great day! :-)