Mini-Split Head location?
I’m planning to install a mini-split soon (I’ll hire a professional to deal with the refrigerant and charge the lines and do everything else myself), but am struggling to sort out the best placement for the interior head.
Background/context: I’m in Seattle and the house is 1 story plus a finished basement (~800sqft on each the main floor and basement). The house is ‘pretty-good’: it was built in 1920, but I’ve reinsulated and aggressively air sealed, including re-sheathing with Zip (the walls are 2×4 with R15 rockwool cavity insulation + continuous R5 comfortboard exterior; attic is vented with ~R50 fiberglass). Currently, we’re heated with baseboard and wall heaters and, except for the coldest days, typically only run the baseboard in the living room and one in the basement, plus a wall heater in my daughter’s room for a few hours at night. I’ve done a manual J and come up with heating and cooling loads of ~13k. I installed an HRV last year with dedicated ducts and stale air exhausts in the kitchen, bathroom and basement, and fresh air supplies in the bedrooms and living room. A floor plan is attached.
Plans: I’m planning to install a 24k Mitsubishi mini-split with one head in the main living area upstairs and one head in the basement. We’ll keep the wall heaters in the bedrooms as supplemental heat. The only location that will really work for the outdoor condenser is on the south side of the house and labelled on the floor plan. I can install an indoor head in the basement on the same wall — so that’s straightforward.
Question: The challenge I’m having is where to install the head in the living area. We don’t really have any walls that are suitable, so I’m going to go with a ceiling cassette. Ideally, I’d like to to install a one-way ceiling cassette on the south-end of the living area, which would keep the refrigerent and condensate lines reasonably short and be visually non-obtrusive — this is the blue rectangle on the floor plan labelled ‘1’. My concern is that given the locations of the HRV supply and exhaust, the mini-split would be pushing against the direction that the HRV is moving the air. I’m not sure if that’s actually an issue or not. If it is, then I could either go with a one-way cassette on the north end of the living area (labelled ‘2’ on the floorplan), which is aesthetically fine, but have a pretty long line run to the condenser; or a standard 4-way ceiling cassette somewhere in the middle of the room (labelled ‘3’ on the floorplan), which my wife and I both think would be ugly, would have a long condensate line and a moderately long refrigerant line, but likely offer the best circulation.
Am I right to be concerned about the mini-split and HRV pushing against each other, or is this not an issue? Are there other considerations or suggestions that that all might have on this?
Thanks!
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Replies
Consider a concealed Duct Mini Split System in a dropped ceiling in the hallway. It could deliver air to almost every room.
https://hvacdirect.com/mitsubishi-se-ka09na-th-8100-btu-15-seer-ductless-mini-split-heat-pump8976.html?utm_source=google&utm_medium=cpc&utm_campaign=20041532371&utm_adgroupid=163569650608&utm_term=&cq_plac=&gad_source=1&gclid=Cj0KCQiAwbitBhDIARIsABfFYILQT1m6fgDHKV_0Min1gDmx01EJ1Rj6AIk7R1agaZMnj29j1QSCfqQaAlXTEALw_wcB
Will the HRV allow you to intake grease kitchen air and moist bathroom air without the grease destroying the heat exchanger and the moisture becoming Ice and stopping the flow?
Walta
Thanks. With regard to the HRV intake, it's not above the stove but about 6 feet away -- it's as far from the stove as I could get it while still being in the kitchen. I'm also a bit confused about the moisture concern. I've consistently seen bathrooms included in the best rooms from which to pull stale air, and the heat exchanger is in a conditioned space. I did quite a bit of research before installing the HRV and followed manufacturer recommendations for intake locations, but please let me know if I missed something important.
The dropped ceiling idea is interesting, but our ceilings are already below 8 ft (old house) and I'd prefer to not lower them further. I could potentially build an insulated box in the attic -- sort of an extension of the conditioned space above the ceiling for a duct run, but there's a lot of electrical, plumbing vents and some roof structure that would have to be reworked and I'm not sure if the juice is worth the squeeze.
There appears to be wall area to the left of your front door (looking out). Mounting a head here would condition the living room and broadcast conditioned air down the hallway to other living areas.
Mitsu heads are intelligent and will sense areas that are deprived and operate accordingly.
If your manual-j is 13k btu, why are you installing 24k btu? That's quite a bit more than you need. I'd consider multiple, smaller exterior units more closely matched to your need than oversizing the system- which will have performance ramifications. This may also help to optimize head placement.
I could potentially mount a wall unit on that section of wall, but routing everything would be challenging. I don't think I could come down from the attic since code won't allow me to drill a large enough hole in the top plate to run refrigerant lines (I believe that a 2.5" hole is typically required and code max without adding steel on a 2x4 plate is a 1.75" hole IIRC). And going straight to the outside would place everything right next to the front door, which my wife would definitely veto. I'd also be concerned about having the condensate drip onto my front porch stairs in the winter. It's worth thinking over though.
In terms of the size, I have the opportunity to get a great deal on a nearly new system with a 24k condenser, two wall heads, and a thermostat ($1000 for everything). Do you think the performance hit would be large enough for the savings to not be worth it?
Also, as Walta suggested, you should not have have an intake to the HRV above the stove for a myriad of reasons. If it's already there, move it!
1. There is no 24k one way cassette. Even if there was this would be a bad choice. Minimum output way too high. 4 way is bad choice there needs a lot of room above it for service and install. The one ton one way cassette or even 1.5 ton would be fine, but by far best choice is PEAD A15AA8 or A18AA8 compact ducted as suggested by Walta. Do not do this yourself, get a professional that will stand behind their work. We get calls every week to repair DIY attempts. Just did one last Friday. Triple zone. The guy actually did a really nice job in some ways, better than many “professional companies.”. Very meticulous, neat job. A few mistakes, mostly the fact that he lubricated the threads on the flare connections. Reduces thread friction and when he torqued the connections to the correct value they were waaaay over compressed and failed. He had orbital flare tool but didn’t matter still had 5 bad connections in one system. Raced cars flared brake lines fuel line etc. Doesn’t matter, not the same.
You don’t know what you don’t know. He had two other people there chasing leaks and repairing, still had problems. They didn’t know how to properly leak test and didn’t use micron gauge. Cost him a lot of money they didn’t fix his problem. One was telling him compressor was bad. Chasing issues that didn’t exist. We found additional leaks, uninsulated pipe inside the house that would have sweat inside the wall, etc. Found the leaks, fixed the leaks, weighed the charge out, weighed in new charge, pressurized lines 600psi nitrogen for a few hours, evacuated 300 micron and commissioned. That’s a couple grand and a LOT of hassle. He also has a 5 zone branch box system he wants us to do the same with after he saw his mistakes on the triple zone. And he has ceiling cassettes that aren’t mounted correctly and have other workmanship issues. You need special tools, knowledge and experience or you’ll be chasing problems in 2-3 years. Pay now or pay later. Get a real install with support and 12yr warranty. Make a good investment. That money you think you’re saving will cost you. Hire with discretion and pay attention. Don’t use ERV as exhaust fan. Keep it clean. Position intakes/outlets so fresh air works toward stale air input and “washes” the space with fresh air.
Your HRV is fine, there are no issues with the pickups as you have them. The bathroom pickup is not a problem as it is not your only one and you are getting mixing from the the other one.
As for units, oversized multi zone is never the answer. Many a people have posted here issues with oversized units with excessive cyling, high power use and comfort issues.
I would get a right sized unit, the slim ducted unit Wata suggested is the way to go. You can mount either above the stairs going to the basement or in the ceiling of the closet there. From there it is a straight shot for most of the ducting to the living space, so you'll only have a small bulkhead above the door of the right side bedroom and another one across the hallway to feed the other bed and bath.
Another option is to go for another brand such as Fujitsu or Midea/Carrier that can be mounted vertically. You can put this on the wall at the end of the hallway and run the ducting in a bulkhead of the hallway. If you go with 6" rectangular trunk, you'll only loose about 7" of height.
Another option is the 4 way cassette with the branch ducts. The nice part about these is the knockouts that let you tap off some of the flow to feed other spaces. Ducting in the attic is not the best idea but if done with care and attention to detail in can work.
https://mylinkdrive.com/USA/P_Series/R410A_Systems-6/Indoor_Equipment-12/Ceiling_Cassette-2/PLA_A18EA7?product&categoryName=Ceiling_Cassette-2
Unfortunately the smallest P series is 2 ton which is also the smallest MXZ it will work with. Again back to way oversized.
One other option is to put a larger mini split in the basement and overheat that space. Think of it as poor man's heated floors. Rough hand calcs says you would have to keep the basement around 78F to have the main floor at 72F assuming no insulation in the ceiling..
Thanks for all of this feedback. Based on what you're all saying here I decided to not move forward with the 24k unit, and I'll go for something smaller, or possible two small condensers. I'm also going to see if I can sort out how to route ducts with a concealed ducted unit -- the way this house is actually built makes some things that look simple on the floor plan nearly impossible in reality (e.g. the section of attic above the stairwell and hallway closet is separated from the rest of the attic by 4x6 headers making a duct run there quite a challenge). That said, I do really like the idea of getting things hidden away.
Take some time read the post about miny system problems.
I think you will find they have a few things in common, almost always the problem systems ate multi splits that have more than one head connected to the outdoor unit, and the systems are oversized.
Please avoid putting your ductwork in the attic. Duct always leaks and if it leaks inside the thermal envelope the leaks are irrelevant. If the leak is outside the thermal envelope that conditioned air is lost. The house will be depressurized and the air will be replaced with unconditioned thru the gaps with huge energy penalties.
I think your plan to find someone to only do the final connections has a few flaws. The big one is the people that do quality work are likely to refuse your offer leaving only the hacks. If you want to do the install yourself look at the MrCool brand DIY line they are plug and play no special tools needed.
Walta
If you do not have a well conditioned attic, a short-run ducted unit is not an option.
As for a unit located next to your front door- open the wall and run the linesets in a stud cavity. No need to run anything in the attic. At the bottom of the cavity, you'll have to incorporate the linesets into some sort of exterior detail or, better, run them through your basement to the condenser. The PVC condensate can turn to the exterior at the base of the wall and be painted to match the siding. You'll never notice it.
If the 2x4 stud cavity proves to be too tight (it shouldn't), you can pad out a chase and conceal with drywall. Thoughtful and concealed installs are possible- if you treat the whole affair as finish work. Which it is.
Mitsuman has give you good advice- hire a professional for the install. I am a GC and pulled split installs in house- the learning curve was expensive and the toolset will cost more than the labor on this particular system.