I have 2600 sq/ft (main floor, basement)in which I want to heat using radiant heat. I know the two ways of installing are embedding in light weight cement,or using alluminum strips (either between floor joists,or directly on the sub-floor).Do you really feel the difference between the two? Also, I want to install a hardwood floor. Will this heating cause gaps in the flooring (besides the regular expansion/contraction that will occur)?

Glen,

Check out Warmboard hydronic subfloor. It's great under hardwood floors and integrates directly into the standard framing system for main floor decks.
www.warmboard.com

Also check out http://www.radiantpanelassociation.org