Parley

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fios

azek classic composite rails

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heat pumps

oversizing is not OK

Understanding turndown For example, the Mitsubishi FS06 wall-mounted ductless unit has a rated cooling capacity of 6,000 BTU per hour and goes down to a minimum capacity of 1,700 BTU per hour. That’s a turndown percentage of 28% (1,700 ÷ 6,000). If you put that unit in a room with a load of 1,500 BTU per hour, it will bottom out nearly 100% of the time it’s running in cooling mode.

Sometimes you’ll see turndown ratio, which is the same concept as turndown percentage but upside down. It’s the ratio of maximum to minimum capacity. For the example here, it would be 6,000 ÷ 1,700 = 3.5. So the turndown ratio is 3.5 to 1, sometimes written 3.5:1.

What happens at part-load? One of the great advantages of using mini-splits is their variable capacity. By oversizing them, you can lose that advantage completely. That 6,000 BTU per hour mini-split in a room with 1,500 BTU per hour of cooling load doesn’t act at all like it has variable capacity because it’s always running at the lowest capacity except on the really extreme temperature days.

When the bottom end of the capacity range is at or above the heating or cooling load, there’s no benefit in part-load conditions. As the heating or cooling load drops from the design load, you want a system whose capacity also drops.

That 6,000 BTU/hr system with a bottom end of 1,700 BTU/hr serving a load of 1,500 BTU/hr doesn’t vary at all in part-load conditions.

When the load is 1,500 BTU/hr (the design load), the system will give you 1,700 BTU/hr. When the load drops to 1,000 BTU/hr, the system will give you 1,700 BTU/hr. When the load is only 500 BTU/hr, the system will give you 1,700 BTU/hr.

Yes, oversizing is a problem

So, yes, you absolutely can oversize a mini-split. And when you do, you end up with some of the same problems you get from oversizing conventional systems: poor humidity control, short cycling, and wasted money.

air to water heat pump AWHP

letters to Arctic

My use for your air to water heat pump products will be limited to DHW and the existing kitchen/bath radiant loop. That might extend to some kind of wall radiant emitters for the other two bathrooms depending on calculating the load and the availability of products matching the load. My needs most closely match the following configuration.

Girl in a jacket

I will set up some monitoring on the existing radiant loop for temperature-in and temperature-out which combined with knowing the flow rate should give me the btu/hr load.

I am not looking for a "quick estimate". What I need from you is performance and engineering data and pricing on all of listed components.

The rest of the house will likely replace 180 degree baseboard emitters with air to air heat pumps connected to some combination of wall units and air handlers.

29 years ago this was a carefully designed system which heats a 2,700 sf house with high ceilings and lots of windows for ~$1,500/yr @ $2.33/therm. I even got John Siegenthaler to weigh in with some invaluable advice.

With electricity here @ $0.27/kwh and natural gas @ .07/kwh it will be a big challenge to design a replacement system. Whatever it is will have to spend most of its time in the operating range that gives you a COP of ~4 or else the operating cost penalty will be too great.

I am licensed builder in MA with EPA 608 universal lic. and am a member of the MassSave Heat Pump Installer Network. So far I have had very good results replacing oil steam boilers with cold climate heat pumps connected to air handlers delivering heat through exposed spiral ductwork running in the conditioned space. Tenants are spending almost half of what oil cost to run their systems.

Heat pumps

drier

whirlpool LU7681XSW2

light bulbs

hallway stairway, all the startrek lights: R7S LED 78MM Bulb Luxvista 5W 3 Way Dimmable LED R7S Base J T3 Type Double Ended Halogen Equivalent
white ceiling reflector lights in mb, stair and kidstudy: Ba15d LED Bulb, New (88LEDs), Ba15d Double Bayonet base, 6W 120v 60W Equivalent, Dimmable
tvroom spots: MR16 LED 2ight Bulb, 90% Energy Saving, 3000K Warm White, 40 degree, AC/DC 12V, 5 Watts, 50W Halogen Bulb Equivalent, GU5.3 Base
mb closet, mirror (maybe kitchen): GU10 COB LED Bulbs, 50W Halogen Bulbs Equivalent, 7W, 550LM, 5000K Daylight White, Dimmable, LED Light Bulbs, MR16 GU10 Base

expresso machine

filter holder 996530029833

fridge

yale appliances 617-825-9253

stove

Bosch model HG18054UC/09 parts select

specs

Bake / broil burner 18,000 / 12,500
front left burner 10,000
back left burner 5,000 
center burner 18,000
back right burner 5,000 
front right burner 15,000