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OT: HVAC Thermostats and Return Air

M

Married2Allis

Well-known Member
I have 1-1/2 story cape code style house with a 4-ton unit with 3 zones: 1st floor, 2nd floor bedroom 1, 2nd floor bedroom 2. There are return-air ducts installed in the ceiling of both upstairs bedrooms. Each upstairs bedroom (zone) has it's own thermostat. The return air ducts work very well in the summer to pull the warm air out of the rooms.

But in the winter time, I'm wondering if the return air ducts are actually pulling the heat out of the room and making the system work harder. The system seems to run too long to maintain the bedroom temp setting of about 70 (68 ok with me, too cold for wifey). Would partially blocking off the returns help ?
 
The circulating fan does not cost much to run, so the furnace may not be working too hard if the fan is running to cool down the unit. You make try running the fan all the time. That will keep the air circulated and the house at a more even temperature. The heat will only come on when the cold air return is below the setting. You may find you can lower the setting a degree or two and still be comfortable with the fan running all the time.

Blocking a cold air return just puts less flow through the furnace and cause it to work less efficiently assuming the system was installed properly to begin with. You might have a HVAC guy check you whole system for efficiency: air velocity, temperature rise across the furnace, temperature loss in feed lines, etc. For maximum efficiency the system should be in balance with the right air flow across the furnace. With multiple zones, if you have one unit the dampers and fan speed controls also need to be checked.
 
Hello Married2Allis,

If the returned air registers are on the wall, chances are
they used the space between studs as a return. If that is the
case just add a register to that. If you do that you can
install regular registers and close-open them as needed. Did
that to my house and worked much better. Top register open in
the summer,(return warm air). Well you know the rest!
Guido.
 
Thanks guido, seems like I could control the return flow better. The return air registers on the first floor are on the wall like you say ... have a top and bottom, top one for summer and bottom for winter (at least that's what they told me).
 
(quoted from post at 14:55:49 01/04/16) Thanks guido, seems like I could control the return flow better. The return air registers on the first floor are on the wall like you say ... have a top and bottom, top one for summer and bottom for winter (at least that's what they told me).
Click to expand...
retty simple to use the empirical method to learn the results. A little plastic wrap & tape..........cover all or part.
 
Hello Married2Allis,

You're welcome! Yep, I told you the same thing. Now you get close one of the return.
Leaving both open will return too much air therefore unbalancing the system. If I
remember correctly return air should be 20-40% of total air output. You cam measure the
output and the return registers and do the math. With air volume and pressure duct design
and shape, there are many variables. I leave that to the engineers. At least you got all
the register you can control,

GUIDO.
 
Married2Allis,
Heat is a form of energy. You will not lose any energy if all your duct work is inside the house,
the heated area. Because heat rises up the stairs to the upper floors, all you will be doing is
sending it to the lower floors. Never block off heat returns. You need good circulation to keep
house evenly heated.

If your house is comfortable, so what's the deal? Can't see blocking off returns will save you any
money.
 
This is my point. The heat rises to the ceiling areas upstairs, why suck it out through the ceiling returns? Why not reduce the return flow to allow the heat to build in the room. If the returns were near the floors upstairs that would make sense, since the cooler air would drop to the floor.
 
(quoted from post at 18:24:44 01/04/16) This is my point. The heat rises to the ceiling areas upstairs, why suck it out through the ceiling returns? Why not reduce the return flow to allow the heat to build in the room. If the returns were near the floors upstairs that would make sense, since the cooler air would drop to the floor.
Click to expand...
top 'thinking'! You could have finished the experiment & KNOW the answer by now. :roll:
 
Thanks for replies. Blocked off the upstairs ceiling return ducts yesterday and opened up the 1st floor ducts to balance the flow. Made a big difference. Seems to really help keep the heat in the rooms. The system definitely ran less frequently and for shorter durations than before.
 
(quoted from post at 08:48:00 01/05/16) Thanks for replies. Blocked off the upstairs ceiling return ducts yesterday and opened up the 1st floor ducts to balance the flow. Made a big difference. Seems to really help keep the heat in the rooms. The system definitely ran less frequently and for shorter durations than before.
Click to expand...
lad you found what you were looking for.....sometimes, life IS simple. :)
 
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