Choosing between ducted and ductless heating
I am currently building a new energy efficient home in the New Hampshire climate zone 4b and am having some difficulty in deciding on the best route for heating the home. I plan on heating with electricity (powered by solar) and like the idea of a ducted heat pump due to its ability to provide consistent heat throughout (also better for resale). However, I have read that efficiency tends to drop with ducted systems. Additionally, it can be difficult to size a ducted system with efficiency in mind, unlike having several ductless mini splits. If I went with a ducted system, the ducts would be within the basement (conditioned space), my assumption is that I would not have issues of heat loss efficiency through the ducts, as the heat would just escape into the home.
Some information about the house I am building.
It is a 1,700 sq ft ranch with an additional 1,700 sq ft conditioned walkout basement. Roughly 2/3 of the basement is below grade. I had a manual J calculation performed by a local professional and the results were as follows.
16,000 BTU’s for the upstairs
8,500 BTU’s for the basement.
For a total combined heat calculation of 24,500 BTU.
The home has 12″ double stud walls with r-40 dense pack cellulose, r-7/8 tripple pane intus windows and r-60 attic. The basement has 2 inches of xps rigid foam on exterior and 3 inches of closed cell spray foam on the interior side. The exterior plywood was taped at all seams, including the sill plate and was then wraped with air sealing house wrap. The interior side of the exterior walls and ceiling was also wrapped with a smart membrane air barrier, so I should effectively have two air barriers with the home (interior and exterior).
I have attached a .PDF which has the house plans and insulating notes on what I just mentioned about the home.
I have narrowed down to two main options for heating and this is where my confusion starts. My HVAC contractor is not used to energy efficient buildings and does not seem to have the expertise in this matter. I am trying to get as close as possible to the Manual J, but also understand that it is only an estimation and could be wrong, so maybe I should plan on slightly over-sizing.
Bryant – Evolution Series 2-ton 280ANV036000 Which has an expected maximum output of 18,000 BTU’s at -5F. At 40F it has a range of 14,000 BTU – 30,000 BTU, which to me indicates it is the sweet spot for not cycling too often.
This system has an HSPF of 13. and a COP of 2.2 at 5F running at maximum capacity.
Since this system would not deliver the full 24,500 BTU when its -15 degrees outside, which happens a few times a year, I would likely have to supplement with electric baseboard which I can do, but is not ideal, although correct me if I am wrong.
The 3-ton version has a maximum capacity of 28,000 BTU’s at -5 degrees F. At 40 degrees F it has a range of 25,000 BTU’s to 46,000 BTU’s. It seems to me the 3-ton version would meet all demand, but would likely cause lots of cycling and losses in efficiency.
It has an HSPF of 12.5 and COP of 2.24 at -5.
2 – Ductless mini-split
A single mini split in the family room, which would draft warm air into adjacent office and bathroom.
——-Mitsubishi MUZ-FH09NA Which has an expected maximum output of 10,900 BTU at 47F and a minimum of 1,600 BTU, At 5F it has roughly the same output with a COP of 2.32 at max capacity (3.13 COP at Min capacity) .
A 2 head unit multi mini split with a head in master bedroom and a head that heats entire basement below. (which will be on the walkout side of home)
——-Mitsubishi MXZ-3C30NAHZ2. Which has an expected maximum output of 28,600 BTUs at 47F and a minimum of 11,400 BTUs. At 5F it has roughly the same output, with a cop of 1.75 at max capacity (2.29 COP at Min capacity)
So here is where I stand, I cant seem to decide which approach is better or if I even have either option dialed in to where they should be. Thank you again and I apologize for the long post!
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