[tom_poconos]

I've been looking for return air registers and noticed almost all of them are lever-less and can't be closed like supply registers. But if I want to shut down a zone, I would want to close both the supply and the return, otherwise the blower will keep sucking unconditioned air out of the room.... right?

 

[SeniorSitizen]

To have air circulation through a room there must be both an innie and an outtie. By closing the innie you don't need to close the outtie.

 

[roughneck]

Do you have a zoned system?
If not, your system isn’t designed to close off airflow to entire rooms.
You cannot close off airflow and expect the system to still function.

 

[tom_poconos]

Ok, now I'm really confused because your answers seem to contradict each other. On the one hand, closing a supply stops airflow to a room. On the other hand, airflow in an un-zoned system cannot be closed off to a room.

I think I understand now why you don't want to close a return though -- it will increase the static pressure... is that right?

 

[roughneck]

It will increase static pressure and reduce airflow. Both are extremely bad for system performance and health.
Those dampers aren’t for completely closing off airflow. Just balancing.
Closing off rooms completely can also cause condensation to form in walls between interior rooms. As they usually aren’t insulated and aren’t meant to have drastic temperature differences.
Closing off rooms will not save you any money or energy either.
In short you don’t want to close rooms off to airflow.

 

[Old Thomas]

Without supply a closed room will not return much. Also, if you close too many returns and forget to open enough, it can collapse ductwork.

 

[roughneck]

Did you get everything straightened out OP?

 

[tom_poconos]

Did you get everything straightened out OP?

Yeh, thank you. I'm more or less resigned to the idea of lever-less returns - but now I'm wondering why do supply registers have levers if stopping airflow is bad? You're also increasing the supply duct pressure then too...right?

In theory, if I have a leaky house (which I do), closing a room's supply would stop airflow, and the blower would still suck air from the room and suck outside air through the cracks and crevices in the walls, windows and ceiling of that room. Then you have cold, unconditioned air hitting the heat exchanger. Right?

Anywho, I guess there are efficiency issues everywhere, you just need to manage them as best you can depending on your setup. My house has no returns at all (blower is just sucking air from the basement), so anything I do is going to be better than what I currently have.

 

[roughneck]

Are you trying to shut off individual rooms with hopes of saving money by not having to condition that room, by closing the dampers?

 

[tom_poconos]

Are you trying to shut off individual rooms with hopes of saving money by not having to condition that room, by closing the dampers?

Yep. I figured closing down vacant rooms would let occupied rooms get to temperature faster.

 

[user_12345a]

Yep. I figured closing down vacant rooms would let occupied rooms get to temperature faster.

There's heat loss from conditioned rooms to unconditioned rooms so savings are minimal.

I don't know why you want "faster", the entire point is to maintain. Equipment only cycles because it has to be sized for extremes.

The dampers are for balancing, not completely shutting airflow to rooms.

 

[roughneck]

No, that’s not the way HVAC functions.
Plus, you’ll almost surely cause damage to your equipment and cause moisture issues in your walls.
Your equipment doesn’t throttle itself to what dampers are open or closed. Even all out zoned systems cannot condition individual rooms. They need a minimum load.
What you are trying to do will not save any energy, and actually could cost you more in energy use.
And you don’t want to short cycle the equipment. Efficiency comes from runtime. Bringing rooms to setpoint fast is bad for equipment life and comfort. And can cause massive humidity problems in cooling season.

 

[roughneck]

OP, do you have any dampers fully closed now?

 

[tom_poconos]

OP, do you have any dampers fully closed now?

None of the supply levers work (they're all stuck open), and there are no returns in the rooms, just a huge open return in the basement. I haven't checked the positions of dampers in the basement but each room gets air so I assume none of the dampers are closed. So whatever I do to the system is going to be an improvement. 120k BTU oil furnace is 25 years old and is going as soon as it's warm out.

 

[roughneck]

You could look into doing a zoned system, but individual room zoning isn’t an option.
You can do individual room control with a VRF system but that’s huge $$$$.
With your old oil furnace, you’ve kinda got what you got.
Basement return is likely not to code. Is the basement finished/conditioned?

 

[tom_poconos]

You could look into doing a zoned system, but individual room zoning isn’t an option.
You can do individual room control with a VRF system but that’s huge $$$$.
With your old oil furnace, you’ve kinda got what you got.
Basement return is likely not to code. Is the basement finished/conditioned?

Basement is unfinished. I haven't looked into zones but maybe an upstairs and downstairs would be nice. How do you prevent the condensation issue with zoned rooms? Seems like this could also happen with mini-split systems which are becoming popular.

 

[roughneck]

Individual zoned rooms are rare. Even with VRF. So it’s not really a standard practice of what to do.
Most residential construction isn’t designed for individual room zoning anyway. There’s no real reason to do it and the return from the initial cost of doing such a system would be non-existent.

 

[roughneck]

Is your basement conditioned? As in insulated and supplied with conditioned air?

 

[tom_poconos]

Is your basement conditioned? As in insulated and supplied with conditioned air?

Hard to say... it's below grade, surrounded by stone and brick on 3 sides but is open to a crawl space at the back (which is below grade, but may have some big leak points.. I've yet to explore it). I'd say there is some air infiltration but it's pretty good. One issue is the heat pump water heater sucks any warm air out of the basement. Radiant heat from the furnace and ductwork provides some warmth. Anyway, this will all be fixed when I add returns to the rooms and stop sucking it from the basement.

 

[roughneck]

I’d imagine your return air isn’t to code, and is creating a huge waste of energy pulling basement air in, that’s open to a crawl space.