Thanks to everyone for the comments so far; keep 'em coming! Responses: @HeProfessional: I will check out the links. I admit that the second one was pretty much incomprehensible to me, but that might have been my late reading time. I'll give it another try. I was worried about the return heat too. What is the maximum temp return heat for efficient condensing boiler operation? Also, does using the boiler for both heating and household hot water make any difference? I would also love a reference to someone in my area who know hydronic and ductless HVAC as most of the information I'm getting so far is from GFA experts. @Jackfre: My research has produced the same results; I think Spacepak is probably off the list. @mike_home: It's a Peerless MI series. Link is below. @fsq4cw: I'll look into that further. I did some research but rejected this option as we live in a flood plain and there are very strict rules on excavating needing to incorporate "make up" soil. Maybe I was too hasty. Here is a link that might be useful: Peerless MI series

chisue- thank you for the info Yes, I am very curious about hydronic heating systems. The upstairs living room and two bedroom are all original oak floors from when the house was built in 1945. I have been told that the radiant floor heating wonÂt work with the wood floors (sigh). The dining space is adjacent to the kitchen and there are ceramic tiles in there and the bathroom is tiled but needs to be replaced someday. So, we could do the radiant heat if it were installed via the basementÂs ceiling (the drywall is newer there but can be done) and install it in the bathroom also via the basement or wait until we replace the floor and do it then. We had another HVAC consultant out last night, said it might be strange to have the heated floors in the kitchen/dining space and not in the living room- I can see that. Plus, we would have to add in the radiant baseboards and I am not sure about those either. The big problem is he roughly quoted the radiant route to be even more expensive than the ductwork and gas furnace! I almost want to go ahead with the ductwork and the gas furnace (He seemed to be pushing the furnace route) but all I keep reading is that it is not an effective form of heating a house. All in all, very confusing. Thanks again and any other input is welcome!

Does the piping have an air elimination valve? This would be near the boiler somewhere, usually between the boiler output and the circulator. The circulator should be at the boiler output pumping the water away from the boiler. The circulator should not be at the return end of the system. Th position of the circulator in the system is important for eliminating air pockets. Is there insulation below the concrete slab? The type of system you have, called a high-mass system, should not be run in a manner which varies the temperature inside the house. Also, high mass radiant should have an outdoor reset controller, to more efficiently react to weather changes. The boiler should have a by-pass loop, which will allow the boiler to run above 140 degrees, preventing condensation. Alternatively, you should have a condensing boiler, which is corrosion resistant and runs at lower temperatures. Can you describe the type of in-slab piping that you have? Length of run? diameter of pipe? Spacing between loops? Electric baseboard heaters are 100% efficient, no matter what kind you get. Heating a house with electricity doesn't seem like something you coulod do with solar cells, as you would need a lot of panels to generate the amount electricity you wuold need..

You say that energy efficiency is important to you. Resistive electric heat of any kind is about as INefficient as heat gets. Doesn't matter whether it's radiant panels or baseboard units or a portable space heater or an oil filled radiator or your carpet pads. They all produce heat exactly the same way. They all will cost exactly the same amount to heat a room to the same measured temperature. They all are equally inefficient. Now, the heater manufacturers will tell you that their heaters are 100% efficient. And they are. They turn 100% of the electricity coming into them into heat. However, the process that makes the electricity is not 100% efficient. Many power plants burn coal or natural gas. A coal plant typically converts about 35% of the coal's energy into electricity. Usually the remaining 65% goes up the stack as waste heat - heating the outdoors. A natural gas plant is a bit more efficient, typically 50% IIRC (I'm sure someone will correct me if these numbers are outdated or I'm remembering them wrong). Newer power plants better these numbers, especially cogeneration plants where they make use of the waste heat, but they still don't get to 100% or even 90%. And then there is further loss in the transmission lines to your home. So which would you rather do? Heat your house with half of the energy in a cubic foot of natural gas, or heat it with nine-tenths of that energy? A good forced air gas furnace can easily be 95-96% efficient. Even a cheap one is 80% efficient. No contest. A natural gas fired hydronic heating system is just as cozy on the feet as your carpet pads. It may not be quite as efficient as a forced air system (depends on installation) but will still easily be in the 80% range or better. Circumstances can alter the equation, of course. Maybe your electricity is generated not from coal or gas, but from falling water (hydropower) or even wind or solar sources. (We won't discuss nuclear energy so as to not "generate" controversy over that.) Or maybe you don't have natural gas service where you live. That leaves LP gas, coal, wood, and a few other fuels. In a sunny region, solar heating may even be viable for part of your heating needs. And of course there's electric heat. The most efficient electric heat choice might depend on where you live. In cold climates, the most efficient electric heat system is a ground source heat pump ("geothermal" heat). It draws heat from the earth. By the "100% efficient" standard of a baseboard heater maker, a GSHP is typically 350% efficient! That is, 1 kWh of electricity gives you as much heat as 3.5 kWh in a carpet pad like you are considering. The downside of a GSHP is usually a relatively high cost of installation. In a very mild climate, an air exchange heat pump will have almost as good a coefficient of performance (COP) as the GSHP. The colder it gets, the less efficient a conventional heat pump is. As you get close to 0 deg F an air heat pump drops to about the efficiency of baseboard heat or your carpet pads. A conventional heat pump is more costly to install than baseboards or carpet pads, but less than a GSHP. This is really just a start, and we're getting off topic here. I suggest you take this discussion over to the HVAC forum.