HVAC Automation Help

I have a two story house with three bedrooms upstairs. The thermostat is currently at the top of the stairs. What I find is that the temp varies 2-6 degrees from upstairs to downstairs and can vary by a couple of degrees in the room from where the thermostat is located.

I'm trying to find out a way to get the temperature in the house more consistent. My first thought was a RCS zoned system but looking under my house it looks like I have that flexible air duct right from the bottom of my furnance to all the vents so I think installing dampners it out.

I've thought about maybe automating the fan on the furnance to run and circulate the house air but not sure if that would help with the temps.

What other ideas are there for getting a handle on the temps. My guess is it involves moving the existing air around some how.

-Josh
 
Don't rule out the zoned system too quickly. You can put dampers in parallel so that several open/close simultaneously.
 
You can also set another unit for the upstairs only. Here in the south all homes have at least 2 units, one for downstairs and one for up.
 
How about something deciding less technical? :(

Count the number of supply registers upstairs and downstairs. Then, locate the return ducts. The problem could be as simple as poor system design. Close all your bedroom doors, turn on your fan, and then put your hand other the bedroom doors. If you feel a strong draft, you might need to balance out the air flow.
 
Running the fan in my 2 story + basement house, smooths out the temperature nicely. I haven't automated it yet, but when I do it'll probably be set to run 5 minutes every 20.

I was thinking about zoning, but I gather you can damage you blower if too many zones are closed and there isn't enough air flow through the system. Kinda like how a vacuum cleaner spins up when you get a clog.

Tim
 
I run the fan for 10 min every hour and it makes a noticable difference in my 2 story. I'm waiting for a zwave fan swtich to get my ceiling fan involved with this event also. I have a two story great room and when I manually run the ran it does an even better job.
 
I've mentioned this a few times before . .

your system(s) needs to be balanced (most residential contractors don't do this !!) . . by this I mean you need to adjust air flow to the different spaces to achieve uniform temp through out . .

you should have manual dampers on the branch duct runs (hard duct or flex to each individual outlet), usually a small handle locked with a wing nut . . if not, get a local hvac contractor to install them . . then with a couple (3-4) instant read thermometers (one in each room) make adjustments until all rooms are cooling/heating evenly . .

(you can use dampers in the registers themselves, but this might create more noise)

make take a little time and effort to get it right, but will do wonders for your comfort level . .

also, the t-stat is usually best in the return air path, you don't want it to be in the air-flow comming out of one of the registers as this will cause short-cycling of the system . .


Pete C

it looks like I have that flexible air duct right from the bottom of my furnance to all the vents

usually the 'bottom' is the return side of the unit, what does the other end look like? . .
 
You can also set another unit for the upstairs only. Here in the south all homes have at least 2 units, one for downstairs and one for up.

This is mostly due to the fact that the biggest 'residential' a/c unit is 5-ton (+/-60000btu/2000cfm) . . down south you need more cooling than one unit can provide in all but the smallest homes . . once your going w/ two units, one up and one down makes sense both load wise and keeping ductwork to a minimum . .
 
I've mentioned this a few times before . .

your system(s) needs to be balanced (most residential contractors don't do this !!) . . by this I mean you need to adjust air flow to the different spaces to achieve uniform temp through out . .

you should have manual dampers on the branch duct runs (hard duct or flex to each individual outlet), usually a small handle locked with a wing nut . . if not, get a local hvac contractor to install them . . then with a couple (3-4) instant read thermometers (one in each room) make adjustments until all rooms are cooling/heating evenly . .

(you can use dampers in the registers themselves, but this might create more noise)

make take a little time and effort to get it right, but will do wonders for your comfort level . .

also, the t-stat is usually best in the return air path, you don't want it to be in the air-flow comming out of one of the registers as this will cause short-cycling of the system . .


Pete C

What about the issue of static pressure? My coolest room is not only furthest from my furnace, but also has the most outside facing walls. This where I should direct most of my air, but I'm worried about closing off the dampers for the rest of the house too much, and those runs being long would generate a high level of resistance, which would increase the static pressure in the ductwork, overspinning my motor and burning it out.

How does one ensure optimal airflow leaving the furnace for the number of dampers open and closed?

Tim
 
Now that we are on the topic of optimizing temperatures in HVAC systems I have a question. In two of our bedrooms the heat register is close to the door. These rooms tend to be 'colder' than others. One of the two is a corner and thus has higher heat loss. I have gone in the register and made sure the internal damper is all the way open but that doesn't seem to make a difference.

It seems to me that the problem is that the damper is close to the door and thus the warm air follows a path straight to the door leaving the room with less heating (e.g. thermal short circuit). It seems like I could redo the ducting to go to the far side of the room (away from the door) and have the warm air 'flow' through the room on the way to the hall way. Alternatively, or in addition to, I could increase the diameter of the ducting (I have good access).

Any thoughts?
 
A second cooling unit is out. This is just a starter home so I'm sure adding a second unit would cost more that just dealing with it also I don't think I'd recoup the cost when I sell the house.

My guess is I don't have the manual dampers on the branches. I'll have to crawl under and look. Again, this is a starter house where all the houses are built by the same builder at I'm sure the lowest cost available. If they aren't there. I will have to look into the manual dampners and see what the cost is.

The thermostat is in the return air path and not by any vent.

The furnace is a down draft furnance. The top end is standard metal duct work from what I can see. But from the bottom of the furnace I see the lines go to all the downstairs registers.

I'll try running the fan and see what that does. I do plan on automating the HVAC probably RCS as you can use the existing thermostat wiring from the control box to the thermostat.
 
What, if any, are the opinions here of having a centrally located return vent instead of having individual returns in each room?
 
What about the issue of static pressure? My coolest room is not only furthest from my furnace, but also has the most outside facing walls. This where I should direct most of my air, but I'm worried about closing off the dampers for the rest of the house too much, and those runs being long would generate a high level of resistance, which would increase the static pressure in the ductwork, overspinning my motor and burning it out.

How does one ensure optimal airflow leaving the furnace for the number of dampers open and closed?

Tim

You should not have to close any damper more than 50% unless you have major design defecencies, and the overall airflow shouldn't change (unless you have very long (>50') duct runs) . . your just making it go where it's needed . .

. . as long as you don't create alot of noise (from the rushing air) while closing dampers you should be OK . . your ears will tell you if you've gone too far . .
 
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