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Gameplan and realistic expectations with a 1920s two story home

user-6094056 | Posted in General Questions on

Dear all:

I apologize up front for such a long question, but I’m feeling pretty desperate. My very pregnant wife and I recently moved to a two-story brick colonial home. We’re pretty handy and have done a lot of the renovations ourselves. But with the baby coming at the end of the summer we’re trying hard to address an uncomfortable temperature differential between the first and second floor — as much as ten degrees, though it feels even worse because of the lack of air flow. The house has a 2.5 ton central air system that relies on ancient duct work. The house feels fine in the winter; the first floor feels fine in the summer. So heat and the second floor is the issue.

We live in central Indiana, climate Zone 5 and about an hour from Indianapolis, and I’ve had the four best local HVAC people (not from Indy) come and bid on it. All four have gone straight to suggesting a second AC in the attic. But it’s even worse than that. None of them suggested we play around with the dampers on the current unit in the basement. None of them suggested more sealing or insulation. None of them even bothered to examine the current second floor vents — which, in a fit of frustration, I started examining myself only to find that one of them had been completely shut off by a damper a foot down the line for who knows how long.

You can bet I removed that damper! But you can also bet I’m really disappointed by the advice from the local contractors. It seems to be, basically, throw thousands of dollars at this problem and end up with an inefficient system that will make your second floor comfortable, but only by overpowering a relatively small space with a second (oversized) 1.5 ton unit.

I’ve been reading a lot online on more holistic and efficient approaches, and I’m hoping I can outline some of my own ideas to you guys — things my wife and I can tackle ourselves. If you see anything more I should do, or anything I shouldn’t do, please say so.

But most importantly I’d love any sense of what a plausible final outcome might be. By taking these steps will I get the upstairs comfortable enough for a newborn without having to put in that dreaded attic AC? Or is a good solution impossible because of the terrible ductwork outlined below? I’d love to have a sense for the house’s potential once I fix some of its problems.

OK, a few more bits of background. I’ve put two numbered, annotated blueprints below. The house, as I said, has two floors that combine for about 1600 square feet (plus an unfinished attic and unfinished basement, which is where the furnace is); it’s got a single brick veneer exterior with no wall insulation (and I’m not really looking to add any given the concerns about moisture). I’ve sealed a lot of the trouble spots in the basement but haven’t done anything in the attic yet. The attic has maybe six inches of cellulose and two small gable vents.

The ductwork in the basement is particularly messy but I don’t see any obvious ways to streamline it. I can try to photograph or diagram it if that’s helpful. Either way, the main problem is that for the second floor the only supplies are three 12″ x 4″ ducts that hidden in the walls — one supplies duct 13 in the guest room, one supplies both ducts 11 and ducts 12 in the bath and second office, and one supplies ducts 12 and ducts 9 in the master and the nursery. (This last one is the worst because it’s got the longest run, which means those two vents get the most feeble air.) There are a few returns downstairs but no returns upstairs.

So here’s my plan.

Phase one:

Put continuous soffit in the gables; put a couple of roof vents high up in the roof; air seal the attic thoroughly; add baffles to protect the new soffit and put another foot of cellulose in the attic to get it over R 50.

Phase two:

At the very least put a return high on the wall in the hallway of the second floor. The easiest spot would be one of the yellow boxes on the blueprint — either 14 or 15. But because space is tight the best I could do would be another 12″ x 4″ duct that I’d stick in a stud cavity. I’ve identified three places where I could run 12″ x 4″ ducts without doing too much aesthetic damage to the house. So maybe I’d end up doing two returns (#14 and #16?) and one more supply (#15?)? Or maybe I just need to focus on more supplies on the second floor?

Or maybe the duct work to the second floor is so anemic that even with the additions and better insulation it still won’t be enough. Maybe I need to think about mini splits (though my wife hates their look) — but then would I need to put one in each of these small, divided rooms? That feels like its own kind of overkill.

I’m really unsure of what to do here. I know I’m going to do phase one regardless because that will help the house in the winter and summer both. But I’m not sure how much phase two (or even phase one) will help with the uncomfortable summers. I’m hoping you guys can offer some guidance. Is a happy ending even possible here?

Finally, thanks for your time — and all those helpful articles and comments I’ve already read on the site.


p.s. The blueprints are attached. Below are some numbered annotations with more info. Blue boxes are supplies; red boxes are returns; yellow boxes are potential spots for more ductwork.

First floor

1. 12 x 30 floor return
2. 12 x 3 baseboard supply

3. 12 x 4 baseboard supply
4. 10 x 4 floor supply

5. 14 x 6 floor return
6. 12 x 3 baseboard supply
7. 30 x 12 floor return

Office 1
8. 12 x 4 baseboard supply

Second floor

9. 12 x 9 floor supply

Bath 2
10. 9 x 4 wall supply

Office 2
11. 12 x 9 wall supply

12. 12 x 9 floor supply

Guest room
13. 12 x 9 floor supply

Easiest hypothetical additions
14. could fit a 12 x 4 duct in the wall here — return?
15. could fit a 12 x 4 duct in the wall here — supply?
16. could fit a 12 x 4 duct in the wall here — return?

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  1. GBA Editor
    Martin Holladay | | #1

    Your HVAC contractors are half right. Although they should certainly have inspected your ducts, they're right that older houses with your problem are best fixed by having two separate AC systems -- one for each floor.

    That doesn't mean, of course, that other contributing factors to your discomfort shouldn't be addressed first. All of these measures can help reduce the temperature difference between floors:

    1. Air sealing work in your basement and attic.

    2. Additional insulation in your attic.

    3. Exterior shading of west-facing windows, especially west-facing windows on the second floor.

    4. Adding dampers to supply ducts serving the first floor, and making improvements to ducts serving the second floor. (Remember to re-open the dampers when cold weather arrives in the fall.)

    Even if you do all of these things, though, your second floor may well remain hotter than your lower floor. If you don't want to install a new split-system air conditioner serving your second floor, you might consider installing a ductless minisplit up there.

    For more information on this problem, see Keeping Cool in a Two-Story House.

  2. user-6094056 | | #2

    Thanks for your reply, Martin. It's inspired a couple follow up questions.

    1) I'm open to a minisplit but worry that the second floor's choppy layout (all those smallish rooms!) will make it difficult. Based on the floor plan I included above, where would you include a minisplit? How many would I need?

    2) I'm definitely going to experiment with the dampers, as you suggest. But I've read on your site and elsewhere that too many modifications can end up freezing the system's coil. How will I know when I've gone too far with the dampers? If I'm just reducing ducts first floor flow instead of shutting them off will I be ok?

    3) I've seen several people on this site dismiss inline duct fans, and I understand why they're a bad idea in 99 percent of cases. But I really think my biggest problem is the long run that supplies the master and nursery (#9 and #12 in the blueprint). There's almost no air there. What about putting a heavy duty inline fan in the basement for that line -- something like this?*Version*=1&*entries*=0

    Is there a chance that fan could create problems elsewhere in the system? I'm fine if it takes air from somewhere else in the house, but I don't want to damage anything.

    4) In terms of halfway fixes, would adding one return in the hallway that follows a 4x12 to the basement make enough difference to be worth cutting up a wall? Or am I just cursed by these limited 4x12 spaces, yet again?

    Again, thanks for your help and your site.

  3. user-6094056 | | #3

    Oh -- and of course I'd still love to hear anyone else's thoughts about my first post, Martin's reply, and my house's best-case scenario. I know that first post is the size of a novel, but I'm really at my wit's end here. Hope I'm not overloading you guys!

  4. Dana1 | | #4

    There is nothing wrong with dropping in half ton window-shakers in the most affected rooms on the upper floor to deal with the comfort issues.

    If springing for a mini-split, it's worth doing the load calculations for both heating & cooling and paying the up-charge for cold climate heat pump version. It's highly likely that a 3/4 mini-split could handle both. It doesn't have to be a wall blob- the floor units are thinner profile and just as efficient, a mini duct cassette mounted in a built-out soffit below the ceiling over the stairwell or in the top of the MBR fairly central to the floor can work. You can move a lot of air through short runs of ~3" x 12" or 4" x 12" hard duct, which would not take up a lot of headroom. Most 1920s colonials have 9.5-10' ceilings,which makes this approach easier than in hobbit-head-banger houses.

    Regarding the existing duct system, if the same ducts are used for space heating, tweaking the flows to optimize cooling will result in a gross temperature imbalance during the heating season. It's probably not worth hacking on them to try to fix this problem.

    The description "...two-story brick colonial..." doesn't tell us much. Is the wall structure brick veneer on a 2x4 framed wall, or is it a double or triple wythe solid brick wall, a masonry cavity wall, or...?? If the walls are uninsulated they can be a real enough fraction of the cooling load. Buy a ~$50 pistol grip infra red thermometer, and track upper floor ceiling and wall temperatures on hot days. It's pretty easy to find gaps in the insulation when the sun has been shining on the wall for an hour or two.

    It's not clear in your drawings where the windows are located. Window gains are a huge part of peak AC loads, particularly west facing windows on upper floors which can't be shaded by overhangs due to low PM sun angles, and are less shaded by adjacent buildings/trees than first floor windows, with the gain happening late in the day after the bricks & attic are already hot. (Martin's #3.) If you have storm windows over the antiques, adding reflective window films on the storm window panes can take down those late day gains down by quite a bit. South facing window gains aren't nearly as big as west facing gains in summer, due to both roof overhangs shading them from mid-day sun, and the high incident angle during the mid-day causing a large fraction of the incident light energy to be reflected rather than transmitted to the interior. It's really the east & west facing windows that are responsible for the bulk of the summertime window gains, and the west gains happen at the worst time of day, so if treating the windows, start there.

  5. user-6094056 | | #5

    Thanks for your reply, D.

    I had not heard about floor units for minisplits -- just wall and ceiling. I'll look into them. With the minisplit you're suggesting a 3/4 ton outside unit and one inside unit? Where would you put it? Or are you suggesting a ducted minisplit inside? I'm nervous about minisplits just because the house is so choppy. Would one minisplit in the hallway help each of the rooms?

    The home does have 9 foot ceilings upstairs. It's single brick veneer with stud framing. The walls are uninsulated but I don't plan to add any -- too many horror stories about moisture in the walls.

    I appreciate your window advice. We do have storm windows, but they're older -- not low-e or anything like that. Adding some film (or at least some good solar blinds inside) is a great idea, starting with the east and west.

  6. Dana1 | | #6

    BTW: If mini-ducted mini split, Fujitsu's RLFCD units can be mounted vertically, which may be easier to deal with, installing it on the south wall of the MBR walk-in with a grille to the hall as the return. It's almost certain that a 9RLFCD would cover both the heating & cooling loads of that space:

    Other vendors' units need to be mounted horizontally, which makes service access a bit more difficult, and takes up a foot of headroom at the cassette itself.

    With a 3/4 ton mini-split on the second floor it's likely to cover the entire cooling load the majority of the time. The "rated" output at which the efficiency is tested is 9000 BTU/hr, but the max output is usually quite a bit higher. (12,000 BTU/hr in the case of the 9RLFCD, which is pretty typical of 3/4 tonners.) With a modulating system with a 4:1 turn-down ratio (some mini-splits have even higher max: min ratios) using a "set and forget" approach results in the lowest power use, since most of the time it will be loping along a much lower speed, and much higher efficiency, thus keeping up with the load is far more efficient than catching-up.

  7. Dana1 | | #7

    Floor mount units look like this:

    If you installed one at the west end of the hall by the stair well and kept all the doors open it would pretty much keep up with the cooling loads.

    Opting to not insulate the wall cavities is a mistake unless there is no sheathing and the studs are smack up against the brick. With more detail on the construction you can get a lot of good advice on this site how to do that without creating moisture issues.

    Window films on the exterior panes is more effective at killing solar gain than blinds. Exterior shutters are more effective than window films, but are pretty expensive to retrofit, and they need to be operated to get the daylighting benefits, unlike window films which work fine even when ignored.

  8. user-6094056 | | #8

    Thanks x2, D! I had not heard of the slim duct minisplit, either, but I think there are two potential spots for it -- that walk in closet you mentioned or the closet between the nursery and the master. It could branch out and cover the whole east part of the house with no problem at all.

    Have you installed the slim duct before? What about putting it behind the wall in the eastern closet (roughly location 14 on my original blueprint) and having it take the return air in at the bottom of the hallway and spit out the supply air at the top? Attached is a picture from the literature you sent of a similar setup for others to see. But that's right by the doors to the nursery and the master -- would that do enough to help them with the doors open? Or do I need short duct runs into each room?

  9. user-6094056 | | #9

    I'll check out the window film, D. Do you have a favorite product for that application?

    I guess I can be talked into insulating the walls, though I'd want to do a lot of research and ask a lot of questions. I think I should probably save that step for after the attic and potentially after a minisplit or inline fan or whatever else I try.

  10. Expert Member
    Dana Dorsett | | #10

    If slim-duct you want to keep the runs pretty short and use only hard piped (no flex) duct, and radiused rather than sharp cornered ells to keep duct friction as low as possible.

    If the hall is going to be use as a common return, doored off rooms need sufficient sized door cuts at the thresholds, or convert a partition wall stud bay into a jump-duct, with a grille near the floor on one side of the wall, and near the ceiling on the other side of the wall. Air sealing that jump duct stud bay above & below the grilles will be of critical importance for limiting air infiltration, since you're creating a huge hole in the wall in a currently uncapped studwall, which would be a gia-normous air leak if left unsealed. By putting the grille high on one side, low on the other a reasonable amount of privacy is maintained with a closed door. If they were at the same level both light and sound would travel pretty freely.

    With the doors open you can probably do just fine with a floor-mount cassette on the west end of the hall. There may be advantages to oversizing it for the higher cfm, but you may have to go to 1.25- 1.5 tons to get the high-flow advantage. If going with something as big as a 1.25 ton, the Fujitsu -15RLFF is probably the better choice than most of the competitors, since it can modulate down as low as 3100 BTU/hr, and would still run somewhat continuously even when oversized for the loads.

    I have not personally installed a mini-ducted system or any other mini-split, for that matter (I'm not in that business), but I've learned how to specify them.

    Air seal the attic floor prior to insulating, including the tops of all studwalls, partition or exterior. If you don't, the convecting conditioned space air at the leak points will condense moisture in the insulation layer during the winter when the attic is cold. This is a common source of mold/rot issues in newly insulated attics when air sealing is ignored.

    If the brick veneer cavity is vented into the attic (which is often the case), you have to take measures to keep that path open, or create a vent path to the outdoors under the eaves. Brick veneer cavities need vent holes at the bottom (called "weep holes" ) to allow air in at the bottom, as well as a path to outdoor air at the top. Often that path is through a vented attic. If the top of the veneer cavity is blocked you can add holes to the outdoors, usually done by drilling a hole in the vertical mortar lines every 3rd brick or so, high enough on the wall that wind driven rain doesn't get in.

    Without a better handle on the material stack-up of the wall from the exterior brick to the interior paint, it's a hard to advise on the safest approach to wall insulation. If the roof overhangs are deep (a foot or so per story) with low direct-wetting of the wall, as long as the brick veneer has a vented convection path to the outdoors insulating the studwall cavities is pretty safe in your climate. The biggest problem areas tend to be around missing or mis-installed window flashing allowing bulk-water incursions. With deep roof overhangs those details matter a lot less, but it still affects the choice of insulation materials.

    This sort of stackup is pretty safe in any climate:

    A 1920s houses would probably have plank or ship-lap sheathing with some sort of tar paper or rosin paper facing the air-gap/cavity and brick, with plaster & lath interior and a number of layers of low-permeance paint. The depth of the cavity matters some- if it's less than a half-inch it can easily become blocked, but otherwise these walls can be insulated a number of different ways. If plaster & lath, the condition of the plaster and the condition of the lath-nails can affect how you go about it too.

  11. user-6094056 | | #11

    Thanks for the detailed answers, Dana. I can't tell you how much I appreciate them.

    The doors upstairs all have at least a two inch cut because previous owners put in tile, then carpet, all of which we tore out to get back to the wood floors. So I think we'd be good there. I'll get up in the attic and check out the brick veneer and so on. I really need to do some more reading on GBA about venting or not venting the attic. Right now it only has two smallish gable vents.

    One question. Is there any reason why you'd put the floor minisplit (if we go that direction) on west side of the hallway instead of the east side? The two rooms on the west side get the best air flow right now, so I think the minisplit would do more good on the east side. Certainly if I do a slim ducted version I would need to put it in the closet on the east side.

    Finally, I'll think about insulating the walls in the next year or two. Maybe I can gather some more info and report back to GBA with questions then.

    Does anyone else have any feedback, or has Dana covered it all? I know Martin said early in the thread that a second system was probably necessary. But I'm thinking I'd like to try fixing the insulation and air sealing first. Then maybe try a minisplit if we still need more cooling.

    One last thing. Does anyone think it's worthwhile to try running some 4x12 ductwork in the wall to add another supply or a return or two for the house's existing system? I mentioned these in my original post and highlighted potential placements in yellow. I just don't know whether the work of cutting into the plaster, etc., to run two more 4x12 ducts will make enough difference to matter.

  12. Dana1 | | #12

    Installing the ductless head on the west side is better than the east because the west side is going to be getting the solar gains late in the day, when the brick and outdoor air temperatures are already hot, and the east side has been out of direct sun for many hours, having radiated & convected away most of what it had gained in the AM when the air temps were cooler.

    Also on the west side with a floor unit there will be convective air flow down the stairwell, covering much of the cooling load for the first floor too. That means the existing ducted unit will be running lower duty cycles, maybe not at all except for peak hours on the hottest days (especially if you go with a 1.25 tonner for the higher blower cfm- which also has higher cooling capacity.) The difference in air flow with the existing unit becomes moot when it isn't running.

    A 1.25 ton unit for a 1600' house is a ratio of a ton per 1300'. For reasonably tight 2-story houses with decent attic-R and no large "sunset view" west windows it really could be enough to cool the whole shebang. I know of a guy in Minneapolis in an ~1800' antique 2 story who cools the whole house with margin to spare using a single 1.5 ton wall coil (a Mitsubishi FE18) at the top of the stair well. His house is probably more air tight than yours is right now, but it's not some ultra-performance house by any means.

    If mini-ducted you can put the cassette where ever it works out best from a duct impedance/ flow point of view. Usually that is somewhere central to the house, not near an exterior wall, since a central location makes all duct runs short.

  13. user-6094056 | | #13

    Thanks, Dana. That makes sense about the sun and heat patterns. On mild days I definitely feel what you're describing. But on warmer days the western part of the house actually feels better because the existing ductwork there puts out a much better flow. I realize you're saying with the right minisplit we could eliminate the need to run the existing unit as much. So I'll have to think about it.

    If we did the floor unit in the hallway do you think the air would get to the various rooms pretty well? These old houses are so choppy, and I worry that even with the doors open one unit won't spread the air fair enough. Maybe I'm wrong there, though.

  14. Dana1 | | #14

    The nursery on the SW corner might need a little help from a fan to exchange cooler air from the hall on the warmest days. The load will be lower if you end up insulating the walls. If the nursery has any east facing window area the AM gains will be pretty high unless you add window films to the storms, or exterior shades or shutters.

    By having a modulating mini-split the cycles will be pretty long, which helps keep the humidity down, making it more comfortable at warmer temps. Most ductless heads can be programmed to run with the blower at high speed, if it turns out to need that to keep the east side rooms comfortable during the warmest weather. That cuts into efficiency a bit since the minimum modulated output with the blower set to high is higher but it's not a huge bite until it's cycling on/off a lot rather than running nearly continuously during the day.

  15. user-6094056 | | #15

    That makes sense -- thanks again. I'm definitely planning to add window film on the east and west windows. Do you have experience with this? I read through the GBA archives but didn't find many specific recommendations. Is the GILA stuff at Amazon and the big boxes OK? Or is there a professional grade product that's better.

    And you mentioned adding film to the storms. Most of what I've read suggests adding the film to the inside of the single pane original windows. Is there a reason to put it on the inside of the storms instead? Maybe just less likely to get bumped / peeled?

  16. user-2310254 | | #16

    @Craig. I used Huber Optik on my previous home. At the time, it seemed to be one of the best aftermarket films available. I believe I used the Ceramic Series. I am not sure if this is available as a DIY product, however.

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