Heating & Air Conditioning The Old House

Remote thermostat for inline duct fan

5 years ago

last modified: 5 years ago

The two-story home we recently purchased (in northwestern New York near Rochester) was built in 1933 with a forced air heating system. Central air was added much later sometime in the 2000's. During heating season, everything works fine and all of the rooms, including the bedrooms on the second floor, heat pretty evenly. However, during the warmer months (like now) when we switch over to cooling, while the main floor is very comfortable, the second floor remains much warmer. After asking some professionals, it turns out that the original ductwork up to the second floor doesn't have the capacity to cool to the degree we'd like it to. So short of replacing ductwork to the second floor or using window units or installing mini-splits up there, I did some research and decided to try inline duct fans to boost the airflow to the second floor. I incorporated an airflow sensor switch which automatically turns on the booster fans when it senses the HVAC system fan coming on and pushing air.

Surprisingly, the inline fans work very well and have made a dramatic improvement in lowering the temperature on the second floor. However, now the rooms upstairs in some instances can get too cold due to this boost in cold air being pushed up to the second floor. So my next challenge is trying to come up with the simplest and least expensive way possible to incorporate a thermostat in each of the rooms on the second floor that will sense the temperature in the room and then shut off its respective inline booster fan down in the basement once the set temperature has been achieved (or allow the fan to turn on in the event the room warms up again). Obviously, these inline fans will only operate when the overall system is running. Wondering if anyone out there had dealt with this challenge and come up with a good solution. Thanks

Featured Answer

charlieny
Original Author

5 years ago

There are several brands on inline duct booster fans. The specific brand I have is Hydrofarm.

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Comments (9)

sktn77a
5 years ago
If I understand your post correctly, you have multiple duct fans (one in the ductwork going to each room). What model fans are they? Are there any adjustments? Will they alter the currently-balanced airflow between floors in the heating season?
charlieny
Original Author
5 years ago
last modified: 5 years ago
Hydro farm 8” fan. Single speed. Fans won’t be used during heating season
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mike_home
5 years ago
I have never dealt with this challenge but I do have a suggestion. The simplest and most inexpensive solution would be to add a cooling line voltage thermostat in series with the booster fan switch. Unfortunately there are not many options for this type of thermostat. This TPI ET9SRTS Series ET9 thermostat should work. Unfortunately there are not a lot of choices and the ones the sell for less than $35 are the mechanical type and not very accurate.

The hard part will be running a 14 gouge wire from the thermostat to the booster fan switch.
sktn77a
5 years ago
"Fans won’t be used during heating season"

No, but they are an obstruction in the ductwork that may well impair airflow when they are not on.

Not sure what to tell you regarding your issue but duct fans frequently cause as many problems as they solve.
HU-867564120
5 years ago
Have you considered these?

https://www.amazon.com/AC-Infinity-Register-Thermostat-Control/dp/B0792QR5YT/ref=sr_1_2?dchild=1&keywords=infinity+airtap+t4&qid=1623770861&sr=8-2
charlieny
Original Author
5 years ago
I have, but unfortunately no manufacturer that I'm aware of makes one for an 8' x 10" register opening.
Lee
5 years ago
I have the same cooling problem and have been wondering how I might go about fixing it. My house was originally a gravity heating system. This idea is brilliant! Do you possibly have a link or name of the fans and thermostats you have been using? I’d be very interested in giving this a try.
wwu123
5 years ago
last modified: 5 years ago
I had a similar challenge with a downstairs office that was furthest from the central HVAC/furnace and too cold in the winter due to insufficient flow, also solved with an inline duct booster that was wired to the furnace accessory (air cleaner) terminals.

1. First, if your duct fan is 120V, have you tried plugging it into a variable speed fan control switch and manually adjusting the speed to balance the flow with the rest of the house? I did this for a few years, and it was somewhat adequate.

2. Second, this past winter I finally installed a DIY zone control board (Smartzone 4X, available from Amazon), to fully zone the office with its own thermostat. Typically zones use duct dampers that open and close for each zone. However, it was almost as trivial to have it control the duct fan instead - i.e turn on the booster fan when the zone was calling for air, and leave the fan off (effectively minimizing the airflow) when the zone was not calling for air. My duct fan is in the crawlspace near the furnace, so the zone control board was within a few feet of both.

The most challenging part was connecting a new thermostat in the office back to the furnace/zone control without tearing open the drywall; fortunately I'd hidden extra cat5e cable in several walls during a remodel, for Ethernet or low voltage automation, and was able to use one for the thermostat wiring.