To save money, re-do your duct work and keep the existing AC. You can replace it later. As for Radiant, I did a staple up in my ranch, and placed 1 1/2 inch foil faced foam boards underneath. I did not want to lift the current floors. It works OK, but If I were doing it again and pulling the floors, I would be more apt to a use a system that layers above the sub floor and under the finshed floor. Wirsbo makes a product like that. It has an aluminum backing too. Not sure if you can take the 5/8 to 3/4 hit in the ceiling height, however. In the bathroom, I would definitley use a sandwich layer, I did it in another house and absolutley love it. Floors are nice and warm. I warmed the shower floor and a bench too. Are you using engineered wood or hardwood? As for the crawlspace, is it a poured or dirt floor? Do water piped run through it. Handling the crawlspace is a whole other conversation. You need to do a heat loss study, than determine the pipe size and pump speed to keep the place warm. I just installed a system 2000 gas unit in my 1500sq-ft ranch with 1 radiant zone and one baseboard loop. It cost about 6k Installed (with indirect 40 gallon water heater) My next project will be an addition on a slab, with radiant in the slab.

A small electric boiler will provide all the water radiant heat you need. It's instant heat and does not maintain a temperature, which means it only heats when there is a call for heat. They are common in the West and Northwest.

I don't know how deep your pockets are or how 'Green' you'd like to be but there is another option you may not have considered about yet. You can keep you hydronic system and with some modification to it have it coupled to a geothermal heat pump. The modifications would allow you to use the geothermal heat pump to heat your home, preheat your domestic hot water and to have central air-conditioning without ever having to install ducts or removing your existing rads. Since we're considering a small area, the cost of geothermal will not be as high as it would be for a much larger system. That coupled with possible tax breaks could make it a viable project. Operational costs could be as much as 70% less or greater than fossil fuels or even electricity. Those that I know who have done this are very satisfied, especially with the central A/C. It's virtually maintenance free with no ducts and no chimney or chimney liners. But the pain is up front as this is the most expensive option. Look at the cost differential between geothermal hydronic and conventional technologies and the tax incentives. SR

Hi ionized and thanks for your reply, Our original house was not built without cooling, our home is in the final stages of framing for an addition out back and moving of walls/major renos in the front portion. Prior to our large addition/remodel we had forced air heating and AC. The HVAC contractor has almost finished up the in floor hydronic heat which will replace the forced air. He started to work on the AC a few months ago, and to our shock installed large 9-10 inch main trunks in our great room and dining room (I posted about the issue at the time and I think you kindly responded). The contractor then explained for the first time we would have lots of these ducts all over the main level. The contractor stopped the progress as we wanted a new AC plan that would minimize the drop downs (contractor went on to some other jobs, and we focused on other aspects of the build as well). We definitely need AC here, our weather would be like Michigan or Buffalo -- lots of brutally hot days for 3-4 months per year. As per the mini-splits we are definitely still considering using them (or ducted mini-splits too). We have heard mixed reviews about mini-splits. I think the main draw back we have been told is the mini-splits need replacing say every 10 years or even sooner, so they don't last as long as central air (hence seen as a less permanent kind of AC). Also, if we go ductless, it will be harder to tie in the HRV unit. Not sure if these warnings are justified or not. The architect and HVAC contractor were down on the mini-splits so made as weary. Cost may also be high with mini-splits, but so is making a conditioned area in the attic I am discovering (not sure yet which is a higher priced solution). A high velocity unit might also be worth investigating. Carol