Hey guys, I know some of you follow my renovation / addition / super-insulation job on here but I am at a new step now. I am getting the addition done slowly but surely and now have a plan for my old fireplace as soon as thats done. I have also conditioned my crawl and put an inch of closed cell spray foam on my roof deck which I plan to increase to 2 inches and an inch of open cell before filling out the rest of the 2x8 cavities with fiberglass bats to get the required R level.

I have been looking at ductless VRFs for my addition and will be putting in at least two heads. I was originally looking to oversize the thing with a multihead system. Like going with a 36btu setup but have it sized for the heat load when it is 17deg outside. Meaning while this thing is only cranking out 17000btus at that temp it is still over my heat load so I dont need backup hear. Well, I just saw on monday that Mitsubishi will be releasing a 30seer / 14something hspf of 12-13. The advantage is that it puts out 10900 btu all the way down to 5def F outside. This year we have already had several single digit days and quite frankly my twin rheem 2 ton units with electric backup have barely kept up with my existing house. Temps have gone into the 60s when I have had a setpoint of 68. For my bedroom an electric space heater fills the gap nicely but runs at 1500watts. At 100% efficiency that is 5000btu but as hot as the cord gets I would think that some of that 5000btu is lost in electrical resistance in the wiring of the house. The mitsubishi is rated at 1500watts max and still produces 10900btu in the process.

I floated this idea to my wife last night and she was frustrated because I just put the rheem units in 3 years ago but... In addition to putting several of these high efficiency units in my addition, put one in our family room and one in our bedroom. I would slowly over the next 5 years or so put a couple more in, one in the kitchen, and one in whatever bedroom we put a kid in when we have one. I would have to reposition one of the thermostats for the old heat pump system but that isnt a big deal. My wife asked why and I told her efficiency. At first it wouldnt be as efficent as having only mini splits but it would be a hell of a lot more efficient than the electric backup heat which I could disable right off get go with two of these units installed in the existing space. Second, the life expectancy on normal heat pumps are like 10 years. I know they last a lot longer if properly maintained but at that same token they run almost 24 hours a day on these cold winter days. I sold our old outdoor unit for $250 when I got rid of it 3 years ago. If I could sell the rheem units at about 10 years I would be happy. My second thought with leaving the old units in place for now would be that they would allow for the heat to be evenly distributed between the smaller rooms like the bathrooms in the house. Eventually, I could put in a small ducted air handler only for bathrooms and closets when I replace the rheem unit. Also, my wife is on my case about when I do the fireplace replacing the vented gas logs we have now with something that looks a little better. Normal vented gas logs run $2500 minimum for a decent set. Going with a ventless system I could get a zero clearance insert for about $500. I am not a fan of ventless but for the short amount of time we run in (maybe an hour a day a couple times a week) I dont think it would be possible to burn up all the oxygen in our home. Mixed with a good carbon monoxide detector and having decreased run time with a minisplit in the room I think I would actually be saving cost of logs and gas vs electricity. Once small unit would also be usable with a generator.

So to sum up, points I am thinking about.

-Multiple minisplits (could be like 8 when this is all said and done) instead of about 3 multihead minisplits. Efficiency vs having 8 small outdoor units.
-Short cycling times on the existing rheem units
-Duct loss for existing rheem units.
-Price difference (cost of about $6000 per 4 units instead of around $5000 for one 4 head setup) Think it will make up for itself since 2 of the 4 head units I would only run 3 wall units and I could piecemeal this in $1500 blocks instead of paying interest on a $5000 setup all at once.
-Touched on above but I could do this a little at a time doing a room every now and then.
-Redundancy, with multiple units if one goes I am not screwed and can replace them one at a time. This again vs looking goofy with 8 of these attached to my house.
-Fireplace vent vs vented and saving in electricity vs propane.


-Possible hybrid scenario to reduce outdoor units. Do our high traffic larger rooms first with the higher efficiency single zone units and possibly install a lower efficiency multizone unit for smaller rooms less used.      


Thoughts please.