$9k to add an HRV?? and other heat-pump questions.
I am in the Seattle, WA area (Climate Zone 4 coastal) and spec’ing a heat pump system to cover my home. The attached diagram shows rough layout of our ~ 5br home (3br + 1 guest br/office + 1 office) with approx Manual J outputs (25.5kBTU/hr heat and 18.6kBTU/hr cool). We are planning our house relatively tight (< 3 ACH50) and have removed all old ducting so are starting from scratch. Unfortunately, attic will be unconditioned, so ducts will be insulated (R9) and buried in dense-blown cellulose (attic is getting R49) — air handler or HRV can go in a tiny plywood box in the attic above a closet that I’m going to make to essentially be conditioned space above a closet just for the air handler.
I can’t quite tell what the best layout actually is here, but my current idea is:
– 1 or 2 outdoor units (cold climate– Mitsubishi H2i)
– 3 – 5 IDUs
– 1x large-ish IDU servicing Living/Dining, Kitchen
– 2-4 small IDU (6k?) in 2-4 bedrooms… only 3 are actually bedrooms
– HRV with supply to BR1,2,3,4; exhaust from office, bathrooms, laundry
– Simple in-line filter box to fit standard furnace filters (MERV13 +)
Maybe I should just tack some HRV-like air-exchange onto the central air option and call it good? I’d love anyone’s input!
I’ve also received a few quotes from my contractor’s HVAC guy and can’t tell if they’re reasonable for the Seattle suburb area, if folks have any thoughts. Does it really cost $9k to *downgrade ODU* & add an HRV to a system like this??
1) $26,900 pre-tax & contractor’s 20% for 48k ODU (MXZSM48NAMHZ-U1), branch box, 5 IDU: 1 x 12k IDU, 2 x 9k IDU, 3 x 6k IDU. *no HRV* Out of the total, design/install cost – $12,900 and materials = $3,185. (sent June 2023, before I did a Manual J and asked him for smaller ODU and to do his own Man J [I don’t think he ever did, but such is life])
2) $35,600 pre-tax & contractor’s 20% for 42k ODU MXZSM42NAMHZ-U1), branch box, 5 IDU: 1 x 12k, 4 x 6k, HRV (LifeBreath RNC155). Out of the total, design/install cost – $18,900 and materials = $5,600. (sent Sep 2023)
3) $28,250 pre-tax & contractor’s 20% for 30k ODU (PUZHA30NKA), 30k air handler (PVAA30AA7), fancy filter box (life breath HEPA for $1k), Wifi remote, *no HRV.* Out of the total, design & install cost – $12,950 and materials = $5,300. (sent Jul 2023)
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Generally, duct as much as you can and #3 seems to do that best. That'll get you a high quality, centralized filter and lets you incorporate the most.
Interesting re "duct as much as you can". Why is that? We'll be burying ducting in insulation, but they'll still be in the uninsulated attic, so I'd imagine there will be some losses if we add more ducting.
As a pollution scientist, I already have a number of HEPA-filter-based air purifier units, so I'm not totally limited by that, but ducting would probably make our heat distribution much more even than indoor wall units. I just want to try and bring this price back down out of the high $30k range back into the high $20k range that it seems I could probably hit (before taxes and whatnot).
Is it bad form to share ducting between a central air handler and an HRV? Or maybe Mitsubishi even has a compatible HRV-enabled air handler, but I haven't been able to find it.
I'm thinking about asking for a specific quote for these line items , what do you think?
- MXZSM36NAMHZ 36kBTU outdoor unit
- SVZ KP36NA MX 36 kBTU indoor air handler unit
- Some form of HRV, maybe a LBT RNC155
- Filter box for MERV13+ (or can the KP36NA handle that in it's 20x20x1 inline filter slot?)
36 kBTU to account for losses in ducts and maybe potential future upgradability ( MXZ series can add a 1+ wall units in addition to the central handler.). Together, these parts would be ~ $10,500. Assume ~ $5.5k in other materials based on other quotes from the HVAC contractor, and that leaves quite a bit for "design & installation" after I've already done much of the non-ducting design already. Based on past quotes, I'd guess this brings me in just under $29k (so ~ $14k for "design and installation" and ~ $1k in rebates he noted). Does this seem like a reasonable assumption / suggestion?
That SM36 does almost 3.5 tons of heat your climate. A bit overkill with a 26k heat load:
https://ashp.neep.org/#!/product/112073/7/25000///0
Probably the 2 ton SUZ/SVZ combination will work. If you feel it is too close, the 2.5 ton will definitely cover but it has a bit higher minimum modulation.
https://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006/M_SUBMITTAL_SVZ-KP24NA_SUZ-KA24NAHZ_en.pdf
I would figure out a spot on the 2nd floor for an air handler and run only the supply ducting through the attic. This also means simple return and easy to add in a larger filter frame for better filtering. Keeps the equipment out of the attic, easier to seal tight and much simpler maintaince/filter replacement down the road.
With fully modulating air handlers the fans run 24/7 so sharing the ducting and using the air handler for fresh air distribution is no extra power cost. Much simpler install and if you want better, you can duct the ERV stale air pickups to the bathrooms. I would expect a simple ducted ERV (one that only connectes to the return) setup to be a couple of grand, not 9k.
Thanks Akos! Wow, I hadn't considered a 2.5 ton system. Lowest I'd looked at was the "SM30." I recalculated my Manual J with ducting **edit: with ducts located above conditioned space ** (previously I was calculating for ductless) and my rated heat load is 27kBTU. With this in mind, does a 32 kBTU system seem crazy high? What kind of issues might I run into with a 32k BTU system if my true need is 27 kBTU?
http://www.mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006/M_SUBMITTAL_PVA-A30AA7_PUZ-HA30NKA_en.pdf
I'd like to get as close as possible, but given the Manual J calcs are mine (and I fear I've made mistakes here and there) and that this is a combo of 1910 and new construction (so not a slam dunk new construction) and it's my first time trying to air seal (i.e, I'll be making a number of errors here, as well), I'd like to err on the side of having enough heat.
Also, got any good leads on an HRV that nicely integrates with the Mitsubishi P series? Or an article or how-to on this that I can read to better understand what I'm asking my HVAC guy to do?
The duct losses will be so low , i wouldn’t even think about them. A ducted system is quieter, more comfortable, easier to replace, easier to incorporate an HRV, subjectively more attractive and more efficient than a multi-split. Multi-splits are generally the worst of all options and should be used only if you can’t fit ductwork.
What are they doing quoting 42k and 48k for a 25k load? Throw those quotes in the garbage.
Yeah. Agreed. Kind of wild. Once I did a Manual J, I was stunned.
A few points:
1. It sounds like you are doing a big renovation, so now is the time to bring your attic into the conditioned envelope. It simplifies many things. I understand if it's truly out of the picture, but some of this HVAC money could be thrown at that problem instead.
2. Don't install 5 indoor units. If ducting the whole thing is actually the simplest option, duct the whole thing. Branch boxes are asking for trouble. They're not bad in principle, but I've not seen a single report of anyone saying "I love my branch boxes. Everyone who works on my system knows exactly how they work!"
3. You're contemplating installing a 3 ton system for a 2 ton heating load and 1.5 ton cooling load. No. Just, no. Install what you need *now* and then add an additional small 1:1 system in the future if necessary.
4. You reference this "contractor's 20%" multiple times. You can't think of things in those terms. You don't dictate a contractor's margin. The bid is the bid and that's it. If you try to squeeze a contractor on their margin, I promise you, as sure as the sun rises and falls, they will squeeze you right back on the install.
5. Whatever further design works needs to be done, get it done before hiring your HVAC contractor. Most have no business doing design, unfortunately. You want to hand them a design that they have to adhere to. This is a contentious thing. It is basically unheard of in residential HVAC. So, you either need a residential installer small enough to go with the flow, or you need a larger company who does commercial as well and is accustomed to getting handed a design.
Pre-replying to myself after re-reading: When you reference "contractor's 20%" are you referring to the HVAC contractor's margin or your GC's margin on top of whatever HVAC option you go with?
If the latter, it seems you're doing a lot of legwork and maybe the GC's supervisory fee should be irrespective of what option you choose.
(But this is also why I am constitutionally incapable of hiring a GC to work on my home, so take that with a grain of salt.)
This is fantastically useful. Thank you!
1. Conditioned attic is unfortunately out of the question for a number of reasons, but my plan is to build a little Air Handler closet above the hallway, seal it and insulate it with polyiso, and treat it as conditioned space while leaving the rest of the attic truly unconditioned. The ducting will be r9 and I am considering creating little poly-iso tunnels (walls on sides and a little ceiling) for the ducting that would then get buried on sides and top with blown in insulation ... at least if the tunnels aren't so tall that they fully protrude out of the r49 blown in that we're getting.
2. Yeah, great idea.
3. Re: 3ton system, I was trying to account for a) the fact that I am doing the manual J myself and might be making mistakes and would rather err on the side of having *enough* heat and b) for losses to ducting that I hadn't yet calculated. But I just recalculated with a ducted system ** edit: with the options for "r8" ducts located "above conditioned space" ** and it only brings my Man J heat load to 27.0 kBTU/hr, so... clearly I was being absurd. I'm angling more toward the single-zone PUZHA30NKA with PVA-A30AA7. It's 32k rated capacity (14k min, 34k max) at 47F (not uncommon in Seattle winter), but I'm hesitant to go lower in capacity. Am I being naive here?
http://www.mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006/M_SUBMITTAL_PVA-A30AA7_PUZ-HA30NKA_en.pdf
4. Good point. All I meant was that it doesn't include certain fees, in case normal costing approaches do include them (for folks to compare and say "sounds normal!" or "sounds pricy!"). The 20% is for the GC, not the HVAC guy. I'm very happy to pay my GC, because he's great and because I never expected him to be as OCD as I am about any of this stuff. It's more the "design fee" from the HVAC guy that I'm way more skeptical of now that I've done so much work and he doesn't even seem to have done a Manual J.
5. What do you mean by further design work? Like actually specifying where ducts go? What size ducts should be? etc.?
On that topic
> What do you mean by further design work? Like actually specifying where ducts go? What size ducts should be? etc.?
Think of it this way...
A first-pass per-room Manual-J that you did is great (seriously, way more work than most contractors are even putting in). But now what? If you don't do a duct design on top of that, how does a contractor install to it? What if something goes wrong? Who screwed up?
If the contractor does a bad duct design (for instance, super long runs of flex) but installs the equipment you specified, they're going to say the design was wrong when things don't perform well.
If you have a comprehensive design including duct design and CFM/room, it's easier to hold the contractor to account if something goes wrong. You hope it never goes that way, but unfortunately sometimes it does.
Again--most residential contractors are going to bristle at this, so you need to come prepared.
Ah, of course. This is great advice. Annoying that one would bristle when I'm paying them through the teeth, but also understandable -- my instinct would probably be to do the same if someone approached me like that in my area of expertise... which, as air pollution science, isn't too far off, I guess.
Got any good tools for doing this? I used CoolCalc for my Manual J and BetterBuiltNW for a general room-by-room design, which does include CFM per room, but is a little more confusing to me and so likely incurred greater error (from me). Maybe I should just fork over $20 for full output from CoolCalc?
Interestingly, the Manual J notes 1,001 total CFM needed, and even the 30kBTU Mitsubishi system indoor unit maxes out at 875 CFM according to specs (link below). Is this an issue?
http://www.mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006/M_SUBMITTAL_PVA-A30AA7_PUZ-HA30NKA_en.pdf
Integrating HRV with central air sounds practical. Regarding costs, $9k for ODU downgrade and HRV addition appears high. Seek more quotes to ensure a fair estimate for your specific needs.