How many ductless head units do I need?

steamheatnewb

Hello - I am looking to install a ductless mini split cooling system in my house (1100sf, 1 floor, 5 room, 2bd).

Do I really need a head unit in each room to cool the place in the summer (I live in New England)?

So far have been getting quotes ~$ for 5 head units totaling 39k BTU. Does this sound like over kill or could I get away with a head unit in each bedroom and a head unit in the living room which flows into the dining room? What is a typical setup like this?

Thank you

pecmsg

1100 Sq Ft shouldn't need 40K BTU's. 12 - 16K tops.
No you don't need a head in each room and in your situation its impractical.
You can do your own Manual "J" Calculation here https://www.loadcalc.net/.
Look into a small ducted unit and pick 3 rooms. The cool dry air will find its wa

steamheatnewb

pecmsg said:

1100 Sq Ft shouldn't need 40K BTU's. 12 - 16K tops.
No you don't need a head in each room and in your situation its impractical.
You can do your own Manual "J" Calculation here https://www.loadcalc.net/.
Look into a small ducted unit and pick 3 rooms. The cool dry air will find its wa

Thank you! Out of curiosity, for that size system with 3 heads, how much do you think it should cost for the install? Assuming just installing the unit and no additional electrical work is needed.

STEAM DOCTOR

We don't discuss price on this forum. Too many variables.....

pecmsg

> @steamheatnewb said:
> (Quote)
> Thank you! Out of curiosity, for that size system with 3 heads, how much do you think it should cost for the install? Assuming just installing the unit and no additional electrical work is needed.
There’s additional electrical needed!

What I charge out here is different then where you are.
Do not shop by price, choose the installing contractor carefully and give them what the want.

EdTheHeaterMan

You can find multi-head outdoor units and put a standard wall unit in the main living area. Then perhaps a small ducted head in a closet between 2 rooms. This will get you down to 3 heads total.

be sure the ducted head can be installed vertically so condensate will drain properly. Not all brands will do this. I have had success with the Fujitsu brand, but there may be others.

read Drain Location specification carefully when installing vertically.


This might be your layout.

You may use 3 indoor units or increase the size of A and delete C and you will only need 2 indoor units. Now you can have something closer the size you need like 25,000 to 33,000 BTU total... (your actual load calculation will determine the proper minimum size)

HVACNUT

Are you committed to ductless? Why not CAC?

steamheatnewb

EdTheHeaterMan said:

You can find multi-head outdoor units and put a standard wall unit in the main living area. Then perhaps a small ducted head in a closet between 2 rooms. This will get you down to 3 heads total.

be sure the ducted head can be installed vertically so condensate will drain properly. Not all brands will do this. I have had success with the Fujitsu brand, but there may be others.

read Drain Location specification carefully when installing vertically.


This might be your layout.

You may use 3 indoor units or increase the size of A and delete C and you will only need 2 indoor units. Now you can have something closer the size you need like 25,000 to 33,000 BTU total... (your actual load calculation will determine the proper minimum size)

Thank you this is great! I haven't looked into duct mini splits too much but I do have a full stand up attic above my condo with full access so it could even work for me to install some duct units between rooms.

This is one unit I saw online that could be similar to what you drew out?
https://www.acwholesalers.com/LG-LMU36CHV-2-LDN097HV4-LDN187HV4-3-PREMTC/p57535.html

HVACNUT

You can certainly do a mini A/H ducted to a few rooms from the attic. Some cassettes even let you run a short duct.

The vertical duct thing looks like a mess IMO. There's too many other less invasive options.

SuperTech

I'd install standard ducted A/C in the attic if you have sufficient space. Regular ducted A/C systems have several advantages in my opinion. Then tend to stay cleaner, are much easier to clean and service. And parts are more accessible and the systems are easier to work on.

Mini splits are great for a lot of applications, but I think a properly designed and installed ducted system is the best option and the first thing to consider for whole house cooling systems.

ratio

Several (most?) mini split mfgrs have air handler 'heads', they operate very much like a standard air handler. A few make an adapter board to connect a mini split outdoor unit to a standard indoor unit, see page 65 of this catalog for instance.

NB: I was thinking about getting this kit for a house I manage, until I heard that it doesn't work with their HP units. And now I can't seem to find it on their website, even though it's still in their catalog. YMMV.

EBEBRATT-Ed

@steamheatnewb

I am in NE and my 1000Ft ranch is all brick and stone no wall insulation at all. I have 2 1/2 tons Manual J was between 2 & 2 1/2 and 2 would have probably done it so the guy with 40K and five heads needs his head examined.

A rough rule of thumb in NE is the cooling load is 1/2 the heating load.

You need an accurate load done first

bio_guy

Ask yourself if window units would be required in every room and you will have an answer to your question about need for a head in each room. A few years ago, I did the thought experiment to add cooling to a central NY (ranch) home with hydronic heat where my parents lived. In the ground level, a couple of minimally ducted units would have handled everything with minimal modifications to the appearance. One in a closet (I was thinking top of the closet) would handle two of the three bedrooms. A second unit in the head space way up in the basement stairway could have almost zero length runs to the kitchen, dining and living rooms. (Service might have been difficult.) That left one bedroom. That could have been handled pretty easily too.

Do try to keep your ducts indoors meaning out of the attic. Leaks in outdoor ducts will draw outside air into the home in unpredicted places. Pressure differentials between rooms will do the same. Creative use of fur-downs for indoor ducts can make them look like an architectural feature. In the case above, an arched plaster passage between two rooms could have been made wider for some custom dimension ducts from the stairwell unit. (A second, higher arch superimposed on one side of the first one might even look elegant.) On the other hand, a very unobtrusive fur-down over a bedroom door could load the other AHU serving the other 2 bedrooms. In this climate, you need relatively little duct for cooling and that helps.