Mini split questions?

[MAX-24-Dean]

My house has 5 bedrooms & a full bath upstairs. Getting heat upstairs is a problem because the ductwork is by today’s standards too small, uninsulated and runs up an outside cold wall.

I’m thinking a mini split may be my best solution.

I have a full basement 1/2 is heated and the other 1/2 is not.

The un-heated side is fan vented outside year round and the basement temperature is 50~70 year round.

I’m thinking that mounting the compressor in this area would make sense and be more efficient than mounting it outside to extract heat in subzerod temps. (Think geothermal temperature stability)

What are your thoughts?

How many btu's of heat do you need upstairs? I believe you are in zone 6 which would be approx. 55 btu's needed per square foot of a well insulated structure.

The smaller the need for heat the more likely that it will work, but you will only get the maximum efficiency until the cubic feet per minute(cfm) air flow at the "outdoor unit" in the basement exceeds the cfm of your fan that runs year round.

I experimented with this in a similiar setting and it worked ok, but it was for a 3/4 ton (9,000 btu) mini split. your mileage may very as my install was in a zone 5 climate.

At some point the temperature in the unheated side of your basement may likely equal the outside temp in the winter as you will be cooling that area with the mini-split to get heat upstairs.

 

[kenmac]

I would say a mini split or a mini VRF would be your best bet

 

[mikester]

I'm happy with my mitsubishi mini-split CCHP's so far. It's -12oF right now and no problem with heat. They work down to -25oF. Keep the outdoor unit out of the snow and out of windy areas. A roof overhang is a good idea too. Place the indoor unit where you want the heat. Mine are very quiet.

 

[bdhsfz6]

Many mini split units have a vertical height limit. You may exceed this if you put the unit in your basement.

A basement unit will also lower the ambient temp in winter and raise it during the summer. Unless you have good floor insulation, this could affect the temp of the rooms above.

 

[Thomas]

Maybe good ceiling fan would help pulling the heat.

 

[Carl_NH]

What's your fuel source - oil, propane or natural gas? Also as others have said putting the condenser in the basement will make it cold (it will transfer heat from basement to the bedrooms) effectively making it colder in the floor above and heated space in your basement. Mini's run down to -14F but the efficiency drops off below 0. We have three units 2 9K and 1 12K Mitsubishi hyper heat ductless (each has its own head) for "heat assist" and summer cooling.

I would get an HVAC expert/estimate to determine if you can use your existing ductwork for the mini system, and then do you have an attic above the bedrooms for ductwork? The ducting/install/mods/labor is probably the biggest expense as the mini split and piping for a 36K unit costs around $5K.

Also check into the MassSaves, and rebates as there is a big push to "electrification" and away from fossil fuels in Ma now, and good rebates/incentives can make it less painful on the pocket.

 

[jjeff]

I put a cheaper 9k btu (less than a 1ton I believe), cost less than 1k$ , for my cabin in the UP it's made by senville. Installed my self with a freinds help who's not an HVAC guy. the HE Aura model has an Arctic heat pump to -20 I believe, works amazing for cooling ok for heating I use a wood stove anyway. cabins a little over 1k sq feet but I splurged when I was building it and hired a foam insulation company used open on walls and closed cell on roof, plus its built into a hillside. The hardest things if your doing it yourself (for me) was purging the lines mine was precharged, and torquing the flare nuts as I didn't have crow foot sockets for a torque wrench at the time. Anyways was thinking ahead when I built my cabin and ran a circuit with disconnect for the unit If I wanted something later (I did). I'm not an HVAC pro btw.

 

[Carl_NH]

Yes jjeff, there are inexpensive units out there that work well and for your application its a great solution. Our 9K Mitsubishi with indoor head and piping I could buy for $1800 and the installer charged $3000 each to buy, install (and warranty for 7 years) and we got a rebate of $400 for each. So for all three of ours was just under $9K installed and with rebates under $8K.

The issue is the OP has 5 bedrooms, ductwork, and to do a ducted system most of the cost is in the labor and ducting than the actual mini split hardware. My neighbor did a whole house renovation, spray foam, (made 2 2000 SF apartments) with a 36K Daikin (3 ton) mini split per apartment - the units total $7K but the ducting and air handler was $12K. Their heat bills run $200-300/month Dec-Mar then summer cooling around $100.

 

[jjeff]

I understand, you can get run multiple units off one condenser I only posted to tell my experience with these and how much I like it.

 

[Mtsoxfan]

I ran a 12k and 18k head off 1 unit and 2 9k heads off another. It ran $16k for parts and labor. With labor shortages going on, I was "lucky" to have it done at that price. Contractors are shorthanded AND there is a building boom up here due to covid.