OT - Heat pumps - ductless vs ducted?

[oldguy00]

Sorry for another OT, figure someone here is bound to be really familiar with this stuff...

We are looking at new houses. Some builders build the houses fully ducted with a full size heat pump unit outside.
Others seem to cheap out a bit and just install a couple of ductless mini splits, along with electric baseboards.

So we are trying to figure out, if we see a house that we like, but it has mini splits, are we looking at much higher heating costs compared to a ducted system?

Houses we are looking at are around the 3000sq ft range, 3 levels finished. Most of the houses with mini splits seem to have one unit on the main (middle) level, and one in the master bedroom on top level. So if you wanted to heat the finished basement, or smaller bedrooms on the top level, you are looking at using the baseboards..

A lot of the googling I've done seems to focus mostly on installation costs, but obviously thats not an issue in my case since we are looking at new houses already built.

Thanks!!

[CDollarsign]

My old house in Cincinnati was built in 1895 and had ductless mini-splits due to the fact that running ducts would cost an insane amount and diminish the historical nature of the home. First off, they are not cheap. I would imagine that the 'hardware' is more expensive than a traditional forced air system.

We liked them and they are super efficient and quiet. They also do a much better job of removing humidity than a ducted forced air system. You can heat/cool just the spaces you want and most of the new ones have wifi integration for controlling via your phone or ipad. They are ugly, but you easily forget they are there after a week or two.

*edit* I didn't read your remark about their locations. You pretty much want them in every room. Although in Canada maybe you don't need cooling everywhere? I would make sure the heat pump is rated for really cold ambient temperatures, as mine was rated to stop heating around 0F.

[vqdriver]

since the question is regarding operating costs, i'll chime in with the standard (and unsatisfying) "it depends" answer. floorplan and living habits will dictate actual heating costs. you could conceivably save because you're not heating space you're not using. meaning, you're hot heating upstairs in the middle of the day when everyone's downstairs. conversely, because there's such a temperature gradient you could see that heaters in those occupied rooms are running all the time because the heat bleeds out to the rest of the house. wall locations and floorplan would affect this the most.

irl, i would think the bigger concern is leaving a heater on when you leave the house. which is more likely if you don't have a central control

[NHAero]

In a 3,000 sf house that is well-built from an energy perspective (you're in Canada, so much more likely than the US - but are you in Saskatoon or Vancouver?) I'd usually be using more than one ducted system using Japanese inverter driven air source heat pumps (generically called minisplits, regardless of whether they are ducted or ductless.) The reason is that the load of each room is too small to justify a separate wall cassette. If the capacity of the outdoor unit is over-sized to accommodate the number of individual room zones, the whole system will run less efficiently, in some cases markedly so.

The best 'minisplit' products have rated output down to -15F without back-up heat. These are generically now dubbed "cold climate heat pumps" and are really different from the traditional US air source heat pumps, which lose capacity as the outdoor temps drop and therefore require back-up heating. Make sure that whatever house you pick has cold climate heat pumps that can cover the load without supplemental heating.

We mostly specify Mitsubishi products, due to a wide product range, good durability, and great engineering support.

I like the ducted systems, as we can make them quieter, and do really excellent filtration on the air stream as well. The problem with using one cassette per floor is that rooms won't get enough heat in severe weather with doors closed and the space with the unit installed will need to be run at higher than comfort temp to get the adjacent rooms to comfort temp.

[oldguy00]

....The problem with using one cassette per floor is that rooms won't get enough heat in severe weather with doors closed and the space with the unit installed will need to be run at higher than comfort temp to get the adjacent rooms to comfort temp.

Thx, we do notice that now. We are in a townhouse right now that has one ductless unit outside, that runs two wall units inside, one on the main level and one in the master bedroom. So of course the 2 smaller bedrooms get very cold if their doors are closed, unless you run the baseboard heaters in them. So I am assuming it will of course be the same issue with a larger house, and the basement will need to use baseboards exclusively.

So I guess still just wondering strictly about operating costs.....for a 3k sq foot house, heating it in the winter, what the diff in cost would be......I guess not easy to answer due to different habits etc.

[NHAero]

Where are you in Canada?
What does electricity cost there?
Thx, we do notice that now. We are in a townhouse right now that has one ductless unit outside, that runs two wall units inside, one on the main level and one in the master bedroom. So of course the 2 smaller bedrooms get very cold if their doors are closed, unless you run the baseboard heaters in them. So I am assuming it will of course be the same issue with a larger house, and the basement will need to use baseboards exclusively.

So I guess still just wondering strictly about operating costs.....for a 3k sq foot house, heating it in the winter, what the diff in cost would be......I guess not easy to answer due to different habits etc.

[oldguy00]

Nova Scotia
15.805 per kilowatt hour

[BobO]

Thx, we do notice that now. We are in a townhouse right now that has one ductless unit outside, that runs two wall units inside, one on the main level and one in the master bedroom. So of course the 2 smaller bedrooms get very cold if their doors are closed, unless you run the baseboard heaters in them. So I am assuming it will of course be the same issue with a larger house, and the basement will need to use baseboards exclusively.

So I guess still just wondering strictly about operating costs.....for a 3k sq foot house, heating it in the winter, what the diff in cost would be......I guess not easy to answer due to different habits etc.

My experience (designing custom homes) is that mini-splits can be wonderful, if each space has it's own unit. Which is normally cost prohibitive. Ducted, forced air systems are used frequently due to being a cost effective way to provide good heating and cooling to the entire home. That being said, heat pump systems are usually not the ideal choice in "cold" climates because they essentially become an electric heat strip furnace at some point. When I design a home for Flagtaff, 7000' elevation with an actual winter, I use a gas fired forced air furnace split system. That combined with a properly constructed building envelope provides excellent performance for surprisingly little operating costs.

[Louis]

These are generically now dubbed "cold climate heat pumps" and are really different from the traditional US air source heat pumps, which lose capacity as the outdoor temps drop and therefore require back-up heating. Make sure that whatever house you pick has cold climate heat pumps that can cover the load without supplemental heating.

They're expensive to install, but I would think that in very cold climates a ground-source heat pump would be the way to go.

[NHAero]

Depends on how you define cold. I have Japanese air source heat pumps in projects in locations significantly colder than Flagstaff without back-up heat. We're seeing Mitsubishi and Fujitsu units running below -20F.

That being said, heat pump systems are usually not the ideal choice in "cold" climates because they essentially become an electric heat strip furnace at some point. .

[NHAero]

When you get to climates like Duluth, MN, for example. I have projects throughout NH and VT with Japanese air source with no back-up heating.

They're expensive to install, but I would think that in very cold climates a ground-source heat pump would be the way to go.

[BobO]

Depends on how you define cold. I have Japanese air source heat pumps in projects in locations significantly colder than Flagstaff without back-up heat. We're seeing Mitsubishi and Fujitsu units running below -20F.

Well, I learned something. I will look into those.

[oldguy00]

Depends on how you define cold. I have Japanese air source heat pumps in projects in locations significantly colder than Flagstaff without back-up heat. We're seeing Mitsubishi and Fujitsu units running below -20F.

Well a typical cold winter day here might be around 10-15F. And we heat the house to somewhere around 68F.
I don't doubt the ability of the mini pumps, again, just wondering if there is a significant operating cost savings with a fully ducted heat pump.

[NHAero]

Here's a good resource to begin:

https://neep.org/ashp

Well, I learned something. I will look into those.

[NHAero]

Depends.
If you compare a fully ducted heat pump where the unit and the ducts are located in an unheated attic (exactly the case I'm doing forensics on today!) then its efficiency and capacity is severely compromised - it's like putting your heating system outdoors. In that case, independent ductless wall or floor cassettes will be more efficient and cost less to operate.

At my house, the ducted system is in the basement, and the basement is insulated. The ducts are sealed against air leakage, and they are insulated. This system has no operating cost penalty vs. separate cassettes, and is right-sized for the house, whereas four cassettes would be twice as much capacity as the house requires.


Well a typical cold winter day here might be around 10-15F. And we heat the house to somewhere around 68F.
I don't doubt the ability of the mini pumps, again, just wondering if there is a significant operating cost savings with a fully ducted heat pump.

[oldguy00]

Depends.
If you compare a fully ducted heat pump where the unit and the ducts are located in an unheated attic (exactly the case I'm doing forensics on today!) then its efficiency and capacity is severely compromised - it's like putting your heating system outdoors. In that case, independent ductless wall or floor cassettes will be more efficient and cost less to operate.

At my house, the ducted system is in the basement, and the basement is insulated. The ducts are sealed against air leakage, and they are insulated. This system has no operating cost penalty vs. separate cassettes, and is right-sized for the house, whereas four cassettes would be twice as much capacity as the house requires.


So with your system, the way you have it setup, is it a lot cheaper to heat your house compared to if you had done it with mini splits?

[NHAero]

Not a lot, but yes it's cheaper. But I have a very well-insulated, small house (1,300 sf), and my specialty is very low energy use buildings, so even if my solar electric system didn't cover the heating, it would cost about $225-250/year even at our exorbitant Martha's Vineyard electric rates. So the decision was made more on the basis of lower sound levels, better filtration, aesthetics, and right-sizing of the system.

So with your system, the way you have it setup, is it a lot cheaper to heat your house compared to if you had done it with mini splits?

[unterhausen]

is it against code anywhere to run ducts in unconditioned space? I imagine it will be eventually. But I think that's what they do nowadays if they can.

[Ozz]

We installed a ductless system about a year ago in our house. They have been great, and no big change in electrical bill.

Previous owners did extensive remodel (additions, etc) but failed to install ductwork that could handle the additional space. We were informed of this when looking to add central A.C. and the tested air handling....determined ductless was the only way to go.

We ended up with a dual head Daikin unit for family room and master bedroom. Provides both heating and cooling.....could not be more pleased.

[NHAero]

AFAIK it's still code legal to run ducts and install air handlers outside of the thermal enclosure of a building in the US. It's really dumb, but legal. The ducts need to be insulated and in theory air-sealed.

When field researchers in FL first understood that slab-on-grade houses with all the A/C equipment in the attic were sucking in 140F humid attic air as a portion of the unit's return air, they calculated that this HVAC practice in FL on a peak cooling day required the equivalent of 17 full size power plants to compensate for placing the systems in the attics.


is it against code anywhere to run ducts in unconditioned space? I imagine it will be eventually. But I think that's what they do nowadays if they can.

[buddybikes]

We had 3 mini splits in our former home put in, great, but 1 died (just after warranty) and another had board burn out. Lots of units - lots of electronics that can fry.

[Rpoole8537]

What is the cost of labor to install one mini split to heat and cool 350 sq ft. Access is simple. Electrician will have to run a power supply.

[Tandem Rider]

As always, with any residential HVAC system, the cheapest way to heat a space is to insulate and airseal the snot out of it. In a perfect building it would be so well done that you would only heat it once and no heat could escape. Exhaust fans, windows, doors, and ceiling lights (among other things) keep that from actually happening. Ductwork will eliminate the need for cassettes hanging on the walls. Real world experience, some of my customers use minisplits in an office or server room, they are pretty reliable, but built like a bic lighter. When they fail, it's usually replacement time. Repair costs are pretty high if they are required.

[speedevil]

This is a timely questions for me. I have a cabin in southern Indiana, near North Vernon. Currently there is a single in-wall AC unit (230v) that cools the main room pretty well. The two bedrooms are on the opposite end of the building and there is no direct path for air to move without being pushed or pulled to them. I'd like to have heat and cooling for the entire upstairs, there's no heat now except for a fireplace downstairs. No ductwork.

I'm thinking a mini-split with two interior units for the bedrooms, and a separate single unit for the main room. The bedrooms are 144 sq ft each, and the main room is about 1000 sq ft. It is very well insulated, but not people friendly in the colder months.

I can run the 230v wiring and can handle the mechanical installation, but I'm not sure what is involved in running the refrigerant tubing. I have a flare tool and pipe bender, so I should be able to run the pipes and cut them to the correct length.

Is there some magic with the installation that I've missed?

[buddybikes]

Want to remind people buying mini-splits - National Grid (or ask your local) provided significant rebate if meets energy star. Also tax deduction.

Our first 3 units cost 7,500 installed, but we got 3,000 back after tax and rebates.

[eddief]

of course you may want to hire a contractor but these are DIY and don't need special handling for refrigerant:

https://mrcool.com/

[NHAero]

The tubing needs to be evacuated to a low vacuum, so you will need some specialized stuff to do this right.

This is a timely questions for me. I have a cabin in southern Indiana, near North Vernon. Currently there is a single in-wall AC unit (230v) that cools the main room pretty well. The two bedrooms are on the opposite end of the building and there is no direct path for air to move without being pushed or pulled to them. I'd like to have heat and cooling for the entire upstairs, there's no heat now except for a fireplace downstairs. No ductwork.

I'm thinking a mini-split with two interior units for the bedrooms, and a separate single unit for the main room. The bedrooms are 144 sq ft each, and the main room is about 1000 sq ft. It is very well insulated, but not people friendly in the colder months.

I can run the 230v wiring and can handle the mechanical installation, but I'm not sure what is involved in running the refrigerant tubing. I have a flare tool and pipe bender, so I should be able to run the pipes and cut them to the correct length.

Is there some magic with the installation that I've missed?

[speedevil]

The tubing needs to be evacuated to a low vacuum, so you will need some specialized stuff to do this right.

I don't have the gauges or the refrigerant to do that work. But I should be able to hire an HVAC guy to check it over and do that part of the job, right?

[buddybikes]

Don't forget you will need to setup 220 line

[speedevil]

Don't forget you will need to setup 220 line

Running the #10 copper for the 230v outdoor terminal/shutoff box is no problem. I'll need to run 2, one for the bedroom compressor/pump and one for the main room compressor/pump.

Are the interior units powered from the compressor wiring, or do they require a separate power source?

it looks like the thermostats can be either wired or wireless/wifi. Would any heat/cool thermostats work with these units or the manufacturer units the only ones that can be used?