I have two mini-split systems with a total of five heads. We use for heat and AC. Our floor plan is not open except between the living and dining rooms. There are 8 foot ceilings except 9 feet in the living room. There is one head in each bedroom, one in the living room and one in the dining room. House is 1440 square feet. If I add up the BTUs of the heads it is 57,000. For some rooms they would have put in smaller indoor units if they had existed. The systems are great but we live in a very moderate climate, Southern California near the coast.

On the sizing, the window u values probably dominate. Do you have curtains and will they be used? A nice thick curtain with good overlap can make a huge difference.

Curious on the costs and do they have back up?

I still think a small system pays back the fastest. Little harm in using the baseboard for the really cold times. You might hit design temp 2 nights a year. And that design temp they are using is probably old and doesn't really happen anymore. Next year will be warmer and so on and so on.

Did you have the j load calculations done be both companies. As to the ac aspect of minisplits, oversized leads to humidity issues as the area reaches temp to quickly and when the compressor stops the fan blows over uncooled water and add humidity to the space. Have your windows, ceilings and square foot precisely measured to determine the proper sizing for your space.

No a/c issues - this is at elevation in Upstate NY. Also minisplits can ramp down pretty low - but I have seen them so oversized that it is still an issue - but not nearly as bad as a conventional that is way oversized.

Ask both installers for the calculations they based their sizing on. Most modern minisplits are inverters that can go down in capacity to match the heating needs.

The winter design temperature for most of upstate NY is 0 degrees F. You will have to look at the specification to see what heat output you will get when you are in the single digits. That is the number that really matters for heating.

A heat pump is supposed to be sized for cooling. At 57,000 BTU your are over sized. If you don't care about cooling, then over sizing should not be a problem. You need a head in the basement if you want to keep it comfortable. I question only one head on the second floor. Is it the area one large room?

Mike - a heat pump is only sized for cooling in cooling dominated areas. You can't size for cooling and be terribly inadequate for heating. It is one reason why conventional heat pumps are most common in milder areas.

You can still care about cooling but you will be oversized in a heating dominated area. That is reason to use minis or staged systems.

@bryanthegrower

Do manualJ first and see what the estimated loads are for your location.

Most software will account for these "ceilings up to 18 feet tall, and lots lots of windows" given your location, the floor plan, type of windows and the insulation. I would not be shocked if 74k will be needed.. Without any data who knows.

David - I agree, in this case the goal is to minimize the heating from electric baseboard. But even upstate NY will get some summer days in the upper 80s. A variable capacity provided by an inverter type system would be the best solution.

bryanthegrower,

In order to see if the 74,000 BTU estimate is realistic, you could compare it to your current electric baseboard heating system. Add up all the power ratings in watts for the current baseboards and multiply the number by 3.412. That will give the approximate number of BTUs your electric heating currently provides. If the baseboard was able to keep the house at 72 degrees in the winter, then that is a good indication of how many BTUs you need.

To give you and idea how the equivalent electric baseboard heating you would need to provide 74,000 BTUs:

74,000 BTUs/3.412 = 21,688 Watts

The other thing you need to find out is how many BTUs will the mini splits produce when running during the coldest nights in the winter. The BTU rating drops with temperature. You need to find out by how much.

Thanks everyone for your input. So right now I have received three quotes. The first quote is for 57,000 BTU, 4 heads/2 condensers total, but this seems underestimated right now. The second quote is for 72,000 BTU, 5 heads/2 condensers, basically adding one more head into the living room.

The final quote I just got is for 100,000 BTUs (!), with 8 heads / 2 condensers using branch boxes. But I have a call in to see if this is correct, as I want to make sure I am reading the quote correctly, it's very detailed.

As many people mentioned above, I am sizing this mostly for heat, as that is where 90% of my needs will be. Couldn't I just turn on some units if I needed AC during the summer?

Of the three quotes, only the second and third company took measurements of my rooms and windows. The first quote now seems a bit too low, and also means that it might not make me eligible for the rebate

@bryanthegrower, what kind of rebate are you looking at?

The biggest quote is $30k in price but they are estimating an almost $15k rebate. What do you think? I am having a hard time making a decision, as I want to get off the electric baseboard, but since it is a new home I don't know exactly how much I am saving each month. There is no record of earlier bills with the energy company either.

How do you get a $15K rebate on a $30K purchase?

My energy provider is central hudson and they are currently providing $1,600/per $10,000 BTU on a heat pump system. My biggest quote is close to 100k BTU

@bryanthegrower, never heard of a utility rebate based on btus. I thought the incentive was on energy efficiency and not size. I know the Feds are doing 26% tax credit on Energy Star HVAC systems this year.

For my energy provider it’s based on btus after they receive a manual J of the houses heat loss and needs

I looked at the rebate form. It says the rebate $1,600 per 10,000 BTU for a cold climate mini split. However the installer must supply a Manual J and Manual S calculation which says you need 100,000 BTU of heating. You also have to use a Hudson Valley Trade Ally installer. Be careful when you are forced to use an installer to get a big rebate. Most of the savings may to the higher price the installer charges because he is an "Ally".

Yeah I considered those things but all the installers here that are trade ally’s handle all the paperwork and calculations to get the rebate. Maybe they are charging more than others but in the end going with a non trade ally and no rebate is prob significantly more expensive than a trade ally + rebate. I’m still get quotes to see what works

Also there are about 200+ allys in my area so I would say it would be harder to find a hvac person that wasn’t one

Right Size for Mini split UNIT.

https://www.cooling-heating.net

9000 Btu|3/4 Ton|(under 400 Sq Feet)

12000 Btu|1 Ton|(400-600 Sq Feet)

18000 Btu|1.5 Ton|(600-800 Sq Feet)

24000 Btu|2 Ton|(800-1200 Sq Feet)

30000 Btu|2.5 Ton|(1200-1500 Sq Feet)

36000 Btu|3 Ton|(1500-1800 Sq Feet)

48000 Btu|4 Ton|(1800-2000 Sq Feet)

60000 BTU|5 TON|(OVER 2000 SQ

Before choice the size, You need considerate the Insulation in your home, how many windows do you have, ect.

These numbers are just very general estimates and not usually right. There’s no way my 1450 sq ft home could be heated with 30000 btu. thats just a fact

Can you call your utility and see what last winter's bill was? Or was it only partially occuppied?

Random not great comparison - we have 48,000 btus in our current house and we are a little oversized. Lets say 40,000 is about right. We paid about $100 for heat last year at $.10 a kwh. Let's say you are double the load and double the kwh cost. That would be $400. Let's say, your colder temps make the heat pump that much less efficient and it is double again - $800.

So we can figure baseboard is 3x higher.

So my best ballpark is $800 for heat pump or $2400 for baseboard using some really pessimistic assumptions per winter.

So your $15k net cost is paid for in about 10 years. The extra maintenance is an issue, the potential repair cost is an issue. And the longevity is an issue - since electric baseboards are too cheap and long lasting.

But - prior utility bills would be a lot better.

Ouch! im fearing my heating bills will be outrageous Like you are estimating but I hope we’re both wrong. unfortunately there’s no previous Heating bills as the house was a foreclosure. your number seem right but I’m still a bit pessimistic that I’ll need 80,000 btu, let’s see.

oops I had read what you wrote too fast and realize those are amounts for the whole winter you are guessing, not each month. What a relief. I am just afraid of what these baseboards will cost but sounds like it would be thousands a winter, not thousands a month, realistically. I’m planning on Still getting The heat pumps but might Be a month or two of colder weather Before they are installed. Thanks again David youre insights have been so helpful during this process.

Bryan,

You've received some good advice here.

And you're being misled by the companies you've rec'd quotes from so far. 100k btu equipment? Unreal.

If your house is anywhere near a load of 40k btu/hr then what you need is air sealing and insulation work first.

They're looking to cash in on the rebate programs and sell you the biggest equipment they can make it look like you need.

You're in for poor comfort and still high utility bills with this level of oversized equipment.

As I stated to you before you reached out to me, we can perform an actual energy assessment on your house and I can give you the load calculations and blower door reading number that gave us those results.

I'd like to add something else,

The model house I've built has a calculated heating load at 5 degrees Fahrenheit of 26,000 btu/hr.

For 3,400 finished sq.ft, or about 28,900 cubic ft of volume.

3,400 sq.ft. & 26,000 btu/hr at 5F.

1,400 sq.ft. and a 30,000 btu/hr @ 5F load is not unrealistic.

But it depends.

Email me some photos & dimensions of your home and I could do a good rough calc.