Winter design temp 28
Heating Degree days 4797
Design Temp 80/64
South facing with lots of windows u28
My question is I have new construction 3000sqft 2 story house. The living room is 2 story the rest will have a 9 ft ceiling. I haven't used the ductless and am wondering with the 2 story living room which would be most efficient and comfortable to heat the main living area. My concern is with the 2 story living room the ductless will be less comfortable because all the heat will go upstairs causing the lower level to be either colder or the upstairs to be hot. The other concern is with the ductless will there be a noticeable breeze. The Radiant would be under floor type with hardwoods.
Do you have any need for cooling or dehumidification? If you don't, I don't see that this would be an application for a ductless heatpump.
You're correct that radiant will not create a temperature gradient between floor and ceiling, and will be most comfortable.
One challenge may be the slow response of radiant due to the mass of the floor - even a wood floor. For instance I do not setback my radiant at night because it simply takes too long. If you have long shoulder seasons where you'd be heating at night and be off during the day, you may want to consider a second zone with panel radiators on the wall, which respond very quickly and are also very comfortable. If you oversize them you can run them at the same temperature as the radiant and won't need a mixing valve.
Now if I was to build a new home for myself right now, I'd use a water to water geothermal heatpump to supply my radiant and go 100% electric.
Why 100% electric.
James wrote 4800 HDD, which I would not consider a mild climate.
Super insulated homes can achieve heat loads so low instead of a geothermal vertical well a slinky can be installed under the foundation at very little cost bringing the price for geothermal down tremendously.
Modern air to air and air to water heat pumps can certainly achieve some very impressive efficiencies, however I am not a fan of them because the outdoor unit harasses the neighbor in dense neighborhoods.
We are a mild climate, tight enclosure. The ductless seems to be very efficient. My objective is to keep the monthly bill lower but comfort is the most important factor. With install costs being similar my concern is with the 2 story living room (18x20). If I use a air heat pump or gas furnace I have multiple vents for each room. With the ductless I have 1 or 2 heads for the main level (about 1100sqft open concept). Will that evenly heat the entire main level?
People mistake the effect of stack leakage as stratification. The distinction is important. Heat wants to equalize. Stratification takes energy. If you do not have large temperature deltas, you will not see the stratification you worry about. If you heat with a wood stove, you WILL see stratification and have the need to mix.
Stack leakage is buoyant heated air rising up and pushing out of your home through high holes, and cold air being sucked in to replace it through low holes (btw, the reverse happens in summer). Often people mistake temperature variance as stratification when it's actually this cold leaking in low, and warm leaking out high. If you have a good enclosure, this leakage is so minimal this variance goes away.
Here are homes in Mass that heat with mini-splits. http://bit.ly/netzeroMass
You get how much colder it is in Mass than where you are? I'm in similar climate in NY and we've had temps in single digits just about every week since November.
We should mention that Transformations' homes in MA have 12" Double Studded R-45 Low Density Foam Walls and typically not a lot of glazing. An 1,800 sqft home may have two mini-splits on the first floor and one on the second floor.
If there is no hot air in the room, there's nothing to rise to the ceiling. In other words if you don't have great heat loss in that living room that would require the mini splits to produce air that is significantly hotter than ambient, you won't have to worry about hot air rising. Pick a quality model with ECM blower and variable refrigerant flow that modulates instead of cycling on and off.
An open floor plan is essential for even distribution on the main level. With a tight enclosure you should have an HRV/ERV with strategically placed exhaust and supply, which will also promote distribution.
Quality of life is very important to me, and I am trying to convince my customers that 'you get what you pay for'.
But each their own and I don't think we're adding value to James' question above. Cheers!