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My home was built in 1985 in the US with conventional HVAC design of that time. Wooden frame house. It has central air conditioning (ducted) and we upgraded to a natural gas furnace recently. We experience both hot and cold temperature extremes in summer and winter, as cold as 0 Fahrenheit and as hot as 102 F.

One of our major problems is that the temperature on the ground floor is often much cooler in the summer and much warmer in the winter than in the upstairs bedrooms. We don’t inhabit the basement ordinarily so the temperature down there doesn’t really matter.

So, if we set the thermostat to 72 Fahrenheit on a hot summer day, an upstairs room will be around 80 with the door open or 85 with the door closed. The living room on the ground floor will be right around 72.

In winter, if the thermostat is set to 70, the ground floor will be 70 but upstairs might be 66 in a room with the door open, or 62 or lower in a room with the door closed.

The longer the door is closed, the worse the temperature difference becomes in the upstairs rooms.

Better insulation could delay the problem, I think, by keeping the heat out in summer and keeping the heat in in winter. However, what ultimately ends up being necessary is to have per room temperature control. With a central blower just blowing the conditioned air equally through all the house’s ducts, this doesn’t seem possible with the current system.

What sort of upgrade should I make that is a balance between affordability and practicality? My end goal is to make occupants in upstairs rooms more comfortable even if they close the door for long periods of time (e.g. while sleeping or talking on VoIP and not wanting to disturb others).

In the winter, an electric space heater is reasonably economical and extremely easy to install (just unbox the thing and plug it in). But removing heat from a room isn’t so easy in summer, when the hallway upstairs is already 80 F or hotter and the outside is 90 or above.

Also consider that the upstairs occupants use plenty of electronics that generates heat - in one room I am dissipating about 750 to 1000 W regularly between a gaming desktop, monitor and several peripherals (router, many wall warts and USB devices, etc.) This extra heat helps in the winter, but increases the desired amount of AC needed to keep the room cool in summer.

Is it possible to upgrade the centralized system where each room can be heated or cooled individually without having to install a space heater and a window mounted A/C unit for each upstairs room? Ideally with a thermostat for each room? What would such a project entail? I’m assuming some significant ductwork would be needed, and a significant HVAC system upgrade?

To do this properly, would I need to have any qualified electricians or HVAC or building code folks get involved at some point, or could I totally DIY it with the right tools and help?


Edit with additional information:

  • All vent registers in the house are 4" x 10".
  • Return register size is about 3x the total area of the output registers and there is one return register per floor. Upstairs return register is near the ceiling, on the wall in the hallway. The hallway is usually the best-calibrated to the set thermostat temperature, probably because there's a huge open airway -- the staircase -- equalizing the temperature between the ground floor and the upstairs hallway.
  • Two small bedrooms and one master bedroom on the upper floor each have one 4" x 10" vent register.
  • The ground floor has two output registers on opposite sides of the floor.
  • The basement has two registers, one in the laundry room and one in the basement proper (which is carpeted and insulated like the living room).
  • All output registers in the basement are closed year-round.
  • Output registers in upstairs bedrooms are usually fully open, but I close them in winter when temperatures are about 45 - 60 F outside, because the occupant of the ground floor keeps requesting the system to put out heat, which makes upstairs uncomfortably warm, especially on the side of the house that is directly exposed to the sun (my bedroom). I leave them open from spring to fall when temperatures are usually warm, and also leave them open when it's very cold outside (because the extreme cold of the outside temp overpowers the seeming "greenhouse effect" that ordinarily makes my bedroom unbearably hot).
  • Playing with register open/closed status over the years hasn't seemed to make much of a difference. For example, I close the registers using the switch and put a strong magnetic sheet on top of the register when I absolutely don't want more heat coming into my bedroom, yet it continues to get hotter and hotter from about 9 AM - 7 PM on a mild winter day when temperatures are around 45 - 60 F.
  • The heat of the sun probably plays a big role in why my room is so hot. The whole side of the house and the roof get belted with sun; solar energy companies are salivating to install solar panels on our roof because we're in the top 5% of solar power production based on our geography and building height relative to nearby buildings and trees.
  • I didn't see any dampers in the HVAC / furnace room.

Unfortunately we don't really have a place to put a second HVAC system on the upper floor. We're already planning to take up more space by moving our laundry equipment from the basement to upstairs to eliminate a 2-floor haul every week (it's hard on my mom's back).

My solution might end up being to just install an A/C unit on the window sill upstairs and use a space heater as necessary. :/

  • 5
    As Tester101's excellent answer suggests, you don't have enough air making it upstairs. In addition to all the excellent suggestions in his answer, there may be one more factor that can help--there might be an installer level blower speed control. (Installer level because it's usually set with an internal jumper.). I'd start with register adjustment as he suggests, but if your finding you need to a little more air thought the system you might be able to get it. Conversely, too much air creates noise at the registers and can be drafty. – Tyson Dec 21 '17 at 15:02
  • Install a ceiling fan above staircases. Worked like a charm for my house. – cgTag Dec 22 '17 at 0:00
  • Install a dual thermostat system, with electric dampers controlling upstairs and downstairs separately. – Hot Licks Dec 23 '17 at 3:24
  • As much as you didn't see them, it really sounds like there are dampers set to winter mode (all the conditioned/heated air going to the basement primarily). I would quintuple check for dampers, and even see about an HVAC contractor coming out to assess and recommend and even make sure there aren't dampers. – Todd Wilcox Dec 23 '17 at 22:13
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+50

Better insulation is always a good choice, though not always the most cost effective.

The cheapest solution, is to adjust the registers. Use the registers to reduce the flow on the first floor, and increase it on the second. This may require closing some of the first floor registers completely. This solution will likely not provide the best results, but may make enough difference in your situation. And besides, it's free.

If you have a little money, and the tools and knowledge to work with ducts. You could install dampers in the ducting. If all the ducting is exposed in the basement, this can be an easy job. Once installed, you can use the dampers to direct the conditioned air where you need it.

If you have a bit more money, you could convert to a dual zoned system. This will require installing dampers, a zone controller, and additional thermostats. This will allow you to control the temperature on each floor independently (sort of).

If you have lots of money, you could install a separate system for each floor. This may not be practical in a smaller home, but is quite popular in larger homes. You'll have a separate furnace and A/C unit for each floor, which are controlled independently of each other by their own thermostats.

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    FYI - My father had a two story with the same problem. You might check just above the Interior Fan Coil Unit and see if there isn't 2 manual dampers already installed. One for the lower floor and one for the upper. We found them and could get some diversity if we adjusted seasonally. Good luck – Retired Master Electrician Dec 21 '17 at 14:27
  • Dual zones is great, but the cost of installation of a second unit, and the upkeep (having to replace 2 units when they fail), never seemed worth it to me. I have a 2-story, mid-sized house with tall ceilings, and have almost eliminated the temperature difference by adjusting the registers alone. Every winter, I nearly fully close all the upstairs registers, and open all the downstairs ones, and in the summer, I cool the house from the upstairs, and close the downstairs registers. Running fans (whether ceiling fans, or HVAC fan) also makes a big difference. – dberm22 Dec 21 '17 at 15:31
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    I had a similar problem installing dampers on the main ducts to the ground floor and to the upstairs was the easiest way for me I would adjust the dampers 2x per year allowing more air upstairs in the summer and more down stairs in the winter that house had the same square footage on both floors and about a 20% restriction balanced both floors quite well. Before adding the dampers I was adjusting all the ducts that was a pain in the butt and took quite a while. The dampers only took a minute to fully open 1 and close the other once I got it close I marked the duct – Ed Beal Dec 21 '17 at 17:31
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    Increasing resistance in (what is most likely to be) a high resistance duct system may not be the best answer. More and better returns will increase desirable conditioned air delivery, and remove pooled air at undesirable temperatures. – kmarsh Dec 21 '17 at 20:04
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In my home I run the furnace fan 24/7 to totally mix all the air in the house all the time.It helps for me and it may help for you. Now, my questions; does your duct system have supply registers and return registers/grills in every room; are the returns installed both high near the floor and near the ceiling in all rooms especially in the top floor; Where are the supply registers located in relation to the doorways and room configurations; do you have an attic above the top floor; what is the temperature drop across the A/C coil in the summer when the A/C is running; and has your system been looked at by a professional HVAC company as to proper sizing of the A/C and ducting sizes? All these questions will help those of us who have worked in the heat/cool business to give you good recommendations.

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    Better with the door open means insufficient returns (and or lack of under cut on the doors) +1 – Mazura Dec 21 '17 at 16:08
  • Good question; there is one single return register upstairs about the size of two sheets of paper next to each other. It’s in the main hallway near the staircase to the ground floor, and located on the wall right next to the ceiling. – allquixotic Dec 21 '17 at 18:02
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    @allquixotic if there's only a single return upstairs, you'll have to leave the doors open, or make sure enough air can move under the doors. – Tester101 Dec 21 '17 at 18:23
  • This answer gets to the heart of the matter. If your furnace is drawing from the basement, temperature stacking during Summer is going to be bad. Many 80's homes have mostly inadequate (too high resistance) ducts and completely inadequate returns. Alternatives are adding returns, running the fan 24/7, or using an ECM air handler fan (turns slowly 24/7). Be aware that running a standard fan 24/7 increases humidity in the home, which may be welcome in some seasons and not in others. – kmarsh Dec 21 '17 at 20:01
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You can also investigate some of the newer smart home options such as a smart thermostat (ie Nest/Ecobee) paired with smart vents from a company like Flair. This combination advertises the ability to sense temperature in each room and automatically adjust individual room vents to achieve desired temperature in each room.

  • This could be a good solution if you like playing with tech, and have lots of money to put into it. – Tester101 Dec 21 '17 at 18:19
  • @Tester101 And aren't worried about your HVAC system being hacked. – JMac Dec 21 '17 at 18:58
  • @JMac I would think that hackers have better things to do than mess with your HVAC system, but maybe I'm wrong. – Tester101 Dec 21 '17 at 21:44
  • @Tester101 It was somewhat tongue-in-cheek; but there seem to be a lot of issues cropping up with these "Smart" technologies. Some of them operate on really accessible channels (this system might not be an issue if it's based on something requiring close proximity). If it communicates online, there's a chance that anyone else could quite easily gain control. It's probably a non-issue; but you do have to be pretty careful with the wireless smart devices. It's not as bad as like wireless home cameras though. – JMac Dec 21 '17 at 21:59
  • @Tester101 this is a proof of concept, but is exactly the type of thing hackers would do: make your home unbearably hot or cold until you either cough up a bitcoin or rip the thermostat from the wall and put the old, "dumb" one back. – user4302 Dec 21 '17 at 23:24
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The big contributing factor here is heat loss (winter) and heat gain (summer) through the building envelope; the upstairs rooms are more exposed to outdoor conditions than the downstairs due to the roof. Heat transfer occurs proportional to the envelope area and the difference in temperature between the room and whatever is on the other side of the wall/floor/ceiling.

I'm guessing you have an attic, is it vented? Venting the attic prevents a lot of heat building up during the summer months; in an unvented attic the temperature is often far warmer than the outside temperature which drives the heat transfer into your upstairs rooms.

In the winter months, venting the attic isn't so helpful for heating the house. You can install insulation for pretty cheap which reduces the rate of heat transfer. Also pay attention to your windows; in many places you can get by without heating as long as:

  • your home is well sealed
  • your home and particularly your windows are well insulated (double or triple pane and filled with an inert gas)
  • you maximize the amount of solar radiation that makes it through your windows and minimize the amount of heat that escapes through them

You can maximize solar radiation coming through the windows by making sure that the blinds are open during the day when the sun is facing them - which you can figure out really easily by orientation. The south sees a pretty even amount of radiation throughout the day (so keep the blinds out of the way), the east sees a lot of sun during the morning hours (so open the blinds in the morning and close them in the afternoon), and the west sees a lot of sun in the evening (so keep the blinds closed until the sun starts to set).

You can also invest in windows with a low emissivity coating which allows solar radiation to come through your windows easily but stops long wave radiation (given off by objects and surfaces in your home due to the temperature) from passing through. These coatings can also be applied to your windows if you don't feel like buying new ones but will likely need reapplied every couple of years.

Now, as for your HVAC. Your thermostat is probably on the ground floor. What about the unit itself? If your unit is in the basement, your ducts have a ways to go before reaching the top floor of your home. Duct insulation is pretty cheap and easy to apply and will help keep the temperature of the air from falling as it makes its way through the duct. Trying to control the system to provide different amounts of conditioned air to different parts of the house requires something besides the uncontrolled supply air grilles you probably have and would end up costing more than just installing a heat pump on the upper floor. You can also try doing a mini-split unit which is cheap and sort of easy to install but you would have to cut a hole in the wall.

Unfortunately getting a fancy thermostat isn't going to solve this particular problem (though if you don't already have a programmable thermostat, they pay for themselves). I would try all of the easy, passive strategies for reducing the heat loss/gain in the upper parts of the home first and then looking into installing a mini-split if that really doesn't help. The good folks over at energy code ace have a ton of best practice guides for installing insulation, windows, HVAC, etc: http://energycodeace.com/content/tools-ace/tool=installation-ace

You can read up on more passive strategies over at the Department of Energy's website: https://energy.gov/energysaver/passive-solar-home-design

I would also recommend getting a $10 IR thermometer which is really helpful for finding leaky areas of your home that need to get sealed up.

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I had the same problem in my house, built in 1950 with tiny ducts. Adjusting dampers helped a little but the real solution was to add a powerful inline blower to the return duct from the second floor. I had it wired to run any time the HVAC blower was running. The hot or cold air coming from the upstairs registers had noticeably greater flow with the return booster running. Before adding the booster the temperature difference between upstairs and downstairs was 10-15 degrees F on the hottest and coldest days. After, it was only 2 degrees F. The only downside was the white noise from the blower that you could hear in the vicinity of the return duct.

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I have a 3 bedroom colonial. The only HVAC returns are just above the 2nd floor floor level, and they are both in the only stairwell. The AC could not cool the upstairs -- the hot air stayed above the returns. I fabricated foam-board channels that go over the return openings and extend nearly to the 2nd level ceiling. qty 6 20"x30" 1/4" thick foam boards, some tape, 2 hooks in the wall over the returns, some string (to hang the channels from the hooks) and 20 minutes of fabrication time. I make 2 straight parallel cuts halfway through the foam boards each about 4" from the long edges -- and fold the boards about 75 degrees away from the cuts forming a channel (and use scraps to brace them in the channel shape without blocking the channel). I tape 3 of these channels in line, I close off the bottom, leave the top open and hang them so the bottoms cover the HVAC returns. So the stairwell is about 4" narrower than usual. But with these ducts in place the returns pull air from the 2nd level ceiling level -- and the AC cools the upstairs MUCH better. About $12 of materials from the "Dollar Tree" makes 2 85" channels (after closing the bottoms). No mods to the HVAC system. Moderately effective for the bedrooms even with the 2nd floor doors closed. Take them down during the winter.

  • You have had many suggestions on how to improve the efficiency of your heat-cool system. Most of the time problems on the second floor are caused by a poorly designed duct system. Centrally located returns are a big problem and are designed to just save the builder-installer money. They are not designed to yield a great working heat/cool system. Usually the ducting is way too small for proper and quiet air delivery and the registers are poorly placed. High and low returns in every room is a must. Run the furnace fan 24/7 to continually circulate the air. Mine has run for 20+ years.and it helps – d.george Dec 23 '17 at 11:50

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