Which system to install: a conventional ducted heat pump or 7 minisplits?
I’m building a 3300 sqft house with blower door test around 1 ach, R31 walls, and a R 60 vented attic in eastern PA (Zone 5). I’m considering using the minisplits from Fujitsu.
My one quote for the conventional system came in for a 3-ton system after he put the house through his software and the other quote was for 7 Fujitsu 9RLS minisplits. It might be overkill with that number of units. I will be ventilating the house with a ultimateAir ERV.
I would like to go with the minisplits for the whole house but I don’t know anyone who has used them. Can anyone give me some advice on the pros and cons for using them or does anyone have experience using them to heat and cool the entire house? By the way, both my wife and I are fine with the looks of them on the wall and with having 7 compressors outside.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
?, building already and the HVAC plans don't exist?
7 splits? Really?
Call Energy Vanguard.
I was in a 5,000 sf custom house the other day, Huge north facing wall of glass- i'd guess 30' at the peak. After one year in the house they are very happy with a six mini spit setup. They have an oil fired radiant floor backup. So ya, really, it works
Why are they saying 7? Can you not use one that coveres several rooms or twin any? Any have several heads per compressor?
I just do not understand. Many super insulated homes use just 1 or 2 heads for 2-3k sqft.
The house is four bedrooms so I thought it best to have one mini split per bedroom and one in living rm, one in kitchen, and one in den area. We were going with one installer and it's a long story but I wanted to get two more quotes. The original HVAC guy wanted to put a 5 ton heat pump system in after his so called engineer worked up the plans but I saw some red flags and decided at the last minute to get another opinion. The second HVAC guy estimated the house to be a 2.7 ton system. I always wanted to explore using mini splits from what I have read but the first guy said they would be over my budget. I personally think he just didn't want to install them or didn't have experience with them. So I asked the third HVAC guy for a price on them and they are totally cheaper so here I am trying to make sure if I make that leap with mini splits that I'm making the right decision. I guess its better late than making this decision than to make a mistake.
Oh and the single compressor single head setup that Fujitsu has gives me 26 SEER where if I go to a multi head mini than I'm at 17 SEER. So I'd rather be more efficient than worry about how many compressors I have.
I'm wrestling with some of the same issues for a renovation. The only downside to minisplits that I've heard (and concern me) is air distribution in small areas (bathrooms, laundry, etc.). This site, which AJ mentioned -- especially the blog -- has been a great source of information:
http://www.energyvanguard.com/
In the spirit of full disclosure, the owner is Allison Bailles, and he's an advisor here at GBA, which is another source of good advice.
(I'm so convinced of the merits of minis, by the way, that I'm considering taking out the conventional in-the-attic ducted system in my project to install minis in the crawlspace.Yes, that's a little kooky. But only a little.)
Curious as to complete HVAC cost quotes when one is quoted 7 splits verses a ducted system? And where are all the 7 outdoor sections going, in one cluster, two clusters, 7 sides of the home...?
john
your tighness seems very good and r values for your zone seem decent too...I dont think you need a head in each room since your losses and differences room to room should be quite small. Allow the ERV to spread the air around and a couple good placed minis to supply the conditioning.
Thanks to all that responded!! We have a quote for eight mini splits for $22,600 but we are going with seven so I'm figuring it will drop to $19,000. Plus, UltimateAir will design the duct work so that hopefully the air will be spread around. The ERV is not included in that price. He said if we buy the ERV at trade price and give hime the ductwork design, then he will do the system ductwork for time and material.
Jesse, I felt it appropriate to have one in each bedroom because all the kids room's are upstairs and when they do move out we can shut those down. My wife is divorced and we have them half the week so we can also turn them down when we don't have them at the house.
AJ we had a single 22 SEER 3 ton heat pump with ducts and same ERV quoted for $31,700 from the second HVAC guy. We are planning on installing two separate groups depending on which mini supplies which room. I'm figuring for the UltimateAir ERV on $2,300 for equipment and $2,000 at the most for ductwork/ labor. So I should be around $24,000 for the job from the third HVAC . The original HVAC guy wanted $38,700 for a Bryant 5 ton ducted system and UltimateAir system.
John, very interesting posts, fantastic prices, sounds like no company mark up included at all. And most here do not include electrician. The mini splits are the heat system too? There is no other heat source? Your electric rate around 15 cents a KWH?
John,
I'm attending a building science conference in Massachusetts. Yesterday I heard R. Carter Scott give a presentation. Scott has built not one but at least 18 net-zero energy homes in the 1,800 to 2,000 square foot range -- all heated and cooled with just 2 ductless minisplits (one in the downstairs living room and one in the upstairs hall.)
As long as your bedrooms don't have unshaded east-facing or west-facing windows (that is, subject to overheating from solar gain), I don't think they need their own minisplit units -- assuming, of course, that you have an excellent envelope and really good windows.
Martin
Do you have additional information on those homes? Zone? 1800-2600 total heated? Any info on type of minis he used?
Jess,
Massachusetts.
Mitsubishi Mr. Slim Hyperheat.
Square footage = total conditioned area.
Martin,
I just read where my house was rated at 36,507 Btuh if I'm reading my heating summary correctly. Even though I may have some overkill with the number of units, I figure by having the mini's in each bedroom I can zone my house better. Plus if I understand this all correctly, the mini's are variable speed so they can ramp down or up in the bedrooms independent of the rest of the house. Are there any down sides to having too many mini's in my house besides the cost of an extra one or two?
John, just one silly downside, your guests may start calling your home Hotel Bell with such nice room amenities... better be up with the program, WSJ at the door every morning and bed turn down service with French dark chocolate bits spread ornately.
John
I would assume the downside is that they would that the units would not run long enough to reach their peak efficiency. It's like driving your car on a lot of short trips, it doesnt get to peak operating efficiency. I have heard that it can take 10+ minutes for a HVAC system to reach efficiency.
Mr. Bell, I think someone should ask: Who did the heating/cooling load calculation? Was it the HVAC people or a qualified third-party with Manual J expertise? I ask because earlier this year I provoked a long thread entitled "Do I Really Need Four Mini-splits?" The answer, in short, was, You don't know until you get a Manual J calculation. I followed the advice, paid the money to a highly-qualified engineer, and found that No, I do not need four mini-splits.
Gordon
The second HVAC guy ran a wrightsoft program on our house and came up with the 2.7 ton rating, hence, the 3 ton system. How do I evaluate my house and what it requires for mini splits? Is it based only on the Btuh of what the software program states that my house requires and or the same for cooling?If that is true then according to the software, my house requires 36,507 Btuh. Using that number that was calculated, I should be installing 3 Fujitsu 9rls2 which is rated 12,000 Btuh each. That, then makes me just shy by 500 Btuh. Considering what has been said in these discussions about he Manual J providing calculations that oversize a system for a house's requirement, l guess that I should be in the ballpark for the right size and number of units. Maybe I'm over simplifying this but I'm just a homeowner trying to learn more and be informed.
John,
I was just asking. Like you, I'm hardly an expert in any of this. Have you read Allison Bailes's post (at Energy Vanguard, also posted on GBA) on his "Rule of Thumb" for HVAC installations? That may also help clarify the issue. Judged by his rule of thumb, I believe 2.7 tons should be in the ballpark. In any case, good luck.
John,
Q. "Are there any downsides to having too many mini's in my house besides the cost of an extra one or two?"
A. Not really, unless anyone is a sensitive sleeper who doesn't like to hear the fan come on. You will also eventually end up with more maintenance headaches, as the units age.
I have lived with mini splits for AC in 2 houses for the last 6 years or so. My current house is 2800 sq ft and has half the insulation of yours and is perfectly comfortable when it is 95F outside in every room with 3 minisplits. Big one upstairs main living space, 2 small 9k units, one in the downstairs family room and one in the master suite.
You do not need 7 minisplits.
When there is no heat source in a room, you do not need ac in it
minisplits 'throw' much further than an air vent of the same output, and have moving vanes to distribute air around.
There are downsides to too many.
Minisplits 'think' a lot, and they never shut off. They want to run at a very low level to be efficient. This means that if they are oversized for the space[as any 9k unit is for a normal bedroom] they are blowing cold air on you when you no longer want it. So you turn it off. then it is stuffy in the morning. Having a more central unit and making it work for a living is better for comfort, especially if you have some means of air exchange room to room.
If I were heating with minisplits I would probably put a little baseboard electric in a far flung bathroom if I thought it was an issue, but with ac only it is not a problem. In my own house[which is a raised ranch with 2 bedrooms downstairs] I could definitely heat with my minisplits, maybe a heatlamp in my master bath, but downstairs would be trickier, I would probably need to establish some airflow to the bedrooms. As you increase insulation levels, these problems tend to go away
Keith G, that is one of the most helpful and insightful comments about mini-splits I have yet seen on GBA. I have copied it for my notes. Thank you!
I met with the HVAC guy and an energy consultant yesterday. We looked for any spots in the house where we might not have enough airflow in ex. walk in closets, bath rms. and laundry rm. We tried to orientate the mini's in a way so airflow will be directed towards those areas and prevent in winter from the hot air from migrating uo the stairwell as best as possible. We also figured where where we could put ERV vents to circulate the air in those areas that are not totally covered by the mini's. I figure if the mini's are working really well, i could just shut one or two down and let the others work at their efficient levels. The I can power the the extra one or two up on those cold days or hot days when we need them. Versatility is what I think is so great about this system. I think also with a little experimentation as we live in the house, we will be able to dial in the optimal performance of the system. Hopefully UltimateAir will provide me withe a great duct design to distribute the air in the house as evenly as possible. I do know of a passive house in the area that only uses one mini to cool the entire 4500 soft house. It's amazing. I guess mini split systems are in its infancy in the US and that conventional systems are still the norm for now. I see where they may be more widely used as people begin to tighten/ insulate their houses better. We will see how my experiment turns out when we move in this fall for our first winter in the house. Whats great is that in the future I may install a PV on the roof to off set my electrical needs.
Thanks to all that contributed.
John- this is jason from UltimateAir- also a PH consultant- and owner/builder of my own 3200 sq ft Passive House. I have two mini split heads.. one outside unit. Dedicated ducting for just ventilation.... yes and UltimateAir ERV... (if you didn't guess.. i get a discount!) One 9K head serving 2200 sq ft and one 9K head serving 1000 sq ft. My house design is very simple, open, and properly shaded (designed by an engineer.. for better or worse)... I'm completely comfortable. I just reviewed your install... and helped with the layout and design. I think you'll be fine. Hope to talk to you soon.
Jason
Thank you for your help. I just wanted to tell every one that I talked to my consultant and both Jason and him talked about my house. According to them, my house should be in great shape with both the mini's and ERV. Jason has looked at my plans and has consulted on what I need for the placement for the exhaust and fresh air needs of my house. I plan on calling him tomorrow about the system hopefully as soon as I get the details from my consultant. I guess as a novice to all of this, I would encourage you to consult him on your ERV needs because he does come highly recommended from my consultant. I feel better after talking today and look forward to talking to Jason tomorrow. I have been told by so many people that everything I'm doing for my house from the thermal envelope to the air sealing that I'm crazy and it won't work. I guess after all of the struggles and watching what is posted on GBA that I've learned a lot. I have been researching all of this for about two years and the house is finally coming together. I will eventually learn of how we and I say WE because of the community on this website has helped me realize this dream of building an energy efficient home to save the almighty dollar. Thank you everyone that has contributed and I'm sure I will still have some question in the future. If anyone needs help or I can assist you in anyway, i will try! I'm not trying to sell you on UltimatetAir but from what I've read and what Jason seems to have contributed to the house, I would encourage you to take a look at their product. After all, I only learned about UltimateAir from this website. Thanks again
Seven or eight of anything isn't a solution, it's a problem.
The 36K heat load number is bigger than the measured heat load number @ +5F, of my 1923 bunglow with 2x4 framing and less than R19 roof, antique double-hungs + storms. It's unlikely your heat load is more than 25K unless you have a ridiculous amount of window area and cheaped out on U-factors.
With R31 walls and decent windows there is no way you would need anything like 1-head per room, but floor plan and where you place the heads is critical. But I'd be surprised if a 3-4 head 3 ton multi-split couldn't be set up to heat & cool a 3300' pretty comfortably at less than half the cost of 7 or 8 3/4-ton units, each grotesquely oversized for their 1-room loads. Being oversized up to 50% for the whole house load has a benefit on operating efficiency since these fully modulating systems run at higher efficiency at lower compressor speed. Oversizing guarantees it's always running at a lower & more efficient speed. Upsizing it to the point where the interior heads or compressor are cycling on & off most of the time rather than modulating cuts into efficiency- 2x oversizing will use more power and be less comfortable than 1.25-1.5x oversizing. So if the true heat load is 25-30K, a 3 ton multi- is likely to be the right way to go.
If you opt for auxilliary resistance heat in the odd room that isn't well served by the head placement, using radiant-cove heaters (mounted at the crown molding) is more responsive and more comfortable, since it's heating the occupant directly rather than needing to raise the temp of the room air.
dana