HVAC help!
I am a homeowner with a 3500 sq ft. home in New York. 10 years ago I purchased an American Standard 16 seer ducted HVAC system. When temperatures go below freezing I have to back up this system with baseboard heaters. Some of my baseboard heaters are newer and some are very old (and probably extremely inefficient). I would love to have a net zero house but I’m not sure if this is possible. Last year I added insulation to the basement and attic. I have solar water heater which is fantastic. I also have sunpower solar panels and wood burning stove that can heat 3000 sq. ft but I don’t want to be be always dependent on it. Heating is my biggest problem in that it takes so much energy. The house uses around 40000 kwh.
I am currently about to remodel my daughters room which has a 10 + year old baseboard heater in it. Could I/should replace it with a i.e. fujitsu mini split? Or should I think about replacing the entire HVAC system? Is there any energy efficient heat pump on the market now that can handle cold New York winters and eliminate my need of baseboard heaters? Thank you so much in advance!!
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Replies
Randi,
If your baseboard heaters are electric, the older ones are just as efficient as the newer ones. All electric resistance heaters have exactly the same efficiency (100%).
Q. "Could I replace the baseboard heater it with a i.e. Fujitsu minisplit?"
A. Yes, you could -- although you may want to come up with a whole-house solution instead of just addressing a single room.
Q. "Should I think about replacing the entire HVAC system?"
A. Perhaps. I would probably start by contracting for a home energy audit by an energy rater who has been certified by RESNET or BPI. The rater will provide you with a report that includes a customized list of the best energy retrofit measures for your home.
Q. "Is there any energy efficient heat pump on the market now that can handle cold New York winters and eliminate my need of baseboard heaters?"
A. Yes. There are many brands of air-source heat pump that can do this. You can choose ductless minisplits, ducted minisplits, or a traditional system that is designed for centralized forced-air ductwork.
Unless your daughter has a VERY large room with lots of window area and substandard insulation, installing even a 3/4 ton Fujitsu -9RLS2 is going to be ridiculously oversized for the actual heating & cooling loads. The 99% outside design temperatures in NY vary -10F in the higher parts of the Adirondacks to +15F Westchester & Long Island- it sort of matters where you are, but the heating output of the 9RLS2 at -20C/-4F is about 10,000 BTU/hr, easily at least 3-5x the actual heating load for a ~200 square foot bedroom, and it's probably more oversized than that if you've taken any measures to lower the loads. (Even a full sized luxury master bedroom suite with his'n'hers walk in closets and a full bath would usually come in well under 10,000 BTU/hr in a code-min house.)
Oversizing a mini-split by more than 1.5x results in less time modulating, lower net efficiency, and overall less comfort. If you're remodeling the room you have an opportunity moment for lowering the heating & cooling loads of that room, and you should keep a running before/after spreadsheet calculation of the heat load to be able to pick something appropriate. Since mini-splits are usually oversized for individual rooms, it may be worth considering incorporating a mini-duct cassette instead of the usual wall unit and using it to heat 2 (or even 3) adjacent spaces. If you don't have at least 7000 BTU/hr of load a standard single-head mini-split would be a poor choice, but splitting a 9000 BTU/hr (cooling rated BTU) mini-duct cassette 2-3 ways with ultra-short duct runs can work out pretty well if the total design heating or cooling load is at least 7000 BTU/hr.
Most of the ducted central heat pump systems fall off a capacity cliff below 0F, whereas the cold-climate mini-splits (Mitsubishi H2i or Fujitsu Halcyon XLTH series) can still deliver at -15F and colder. But if you live in a location where the design temp is above +10F and your house is pretty tight & well insulated (may need some work if that 40,000 kwh/year number is all just for heating, mostly with a heat pump), you may be better off replacing the existing heat pump a Carrier Greenspeed or Lennox XP25 or similar high-efficiency variable-speed ducted system size to have sufficient capacity to cover the load at the 99% design condition (as determined by a Manual-J or similar load calculation, if not a full energy use simulation tool.)
Randi,
The Lennox XP14 is an air-source heat pump with specs listed down to -15 degrees F
https://www.greenbuildingadvisor.com/sites/default/files/XP14_expanded_pg3.pdf
Heating capacity is 11,000 Btuh at 5 degrees F and 5,800 Btuh at -15 degrees F
" Heating capacity is 11,000 Btuh at 5 degrees F and 5,800 Btuh at -15 degrees F"
Even a PassiveHouse has a heat load well over 5,800 BTU/hr @ -15F. Some PassiveHouses might have a load of 11,000BTU/hr @ +5F though. (If it did the XP14 still probably isn't the right solution.) The output at +15F (the 99% design temp for NYC & most of L.I.) is only 14,000 BTU/hr, which is probably less than half the heat load at that temp of any house that uses 40,000 kwh/year with a combination of heat pump + baseboard.
So while the XP14s have a rated output at -15F it's not exactly a meaningful amount capacity for a 3500' house even if it were super insulated. It's output at -15F is comparable to one 1500 watt electric baseboard (and it's efficiency at that temp about the same.) A 3/4 ton cold-climate mini-split has considerably more output than that at -15F, and would use only half the power of it's baseboard-equivalent.
Play around with this tool a bit: http://www.tools.carrier.com/greenspeed/ Click on the "Heating Capacities" tab then set the design temp to yours, and view the output curve across temp for different combinations of indoor unit and outdoor unit. You'll see that while the 3 ton unit (25VNA036A) combined with the FE4AN air handler can deliver over 30,000 BTU/hr @ 15F (which could be the heat load of a decently insulated & tight 3500' house with an insulated foundation), it's capacity at +5F is still a fairly decent ~25,000 BTU/hr.
But it's capacity at -5F is only ~18,000 BTU/hr (about the output of the1.5 ton MSZ-FE18NA mini-split at -5F) and at -15F delivers only a dismal 11-12,000 BTU/hr, about what you get from a 1.0-1.25 ton cold-climate mini-split. The curves for the XP25s are similar, though the series has sizes from 2 to 5 tons, whereas IIRC GreenSpeeds top out at 3-tons.
If your 99% outside design temp is sub-zero and your binned hourly mean temp in January is in the mid-teens (say, Saranac Lake or Lake Placid) there are very few ducted heat pumps that come anywhere near carrying the whole load (or even the average load well), but if you're on Long Island where the 99% DESIGN temp is +15F (the average January temp for Lake Placid) and the binned hourly mean is about the freeze point (or higher) these systems can work out just fine.