Controlling Wall Fans with Thermostat
Is it possible to control a fan with a thermostat?
I live in Massachusetts. I have a 1,700 s.f. house built in 1973. The open living area has a cathedral ceiling. I plan to retrofit the whole house with heat pumps. I want to maintain a comfortable temperature in the home office and two seldom used bedrooms. All three of these rooms are small – about 120 square feet. It would be expensive to equip each of them with its own heat pump. Could I put a fan through the wall of each room to mix the air in these rooms with the air in the main living area? See attached floor plans.
The main living area will be maintained at about 70ºF by two one-to-one ductless mini-split heat pumps. I envision a thermostat in each of the three small rooms that would turn on the wall fan whenever the room gets warmer than 70ºF in summer or cooler than 70ºF in winter. By mixing the air in the smaller rooms with the air in the main living area, the temperature in all the rooms would presumably stay at the temperature called for by the thermostats on the heat pumps in the main living area.
Have you ever heard of anyone doing something like this? Are off-the-shelf thermostats for fans available?
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Carl Seville, Green Building Curmudgeon, did something like this in his house. As I recall, all the calculations indicated it would not work, but he reported back that his installation in fact does work. See the comments for the full discussion.
https://www.greenbuildingadvisor.com/article/done-well-almost
This post also discusses the fans:
https://www.greenbuildingadvisor.com/article/getting-into-the-details
Thank you very much for this reference! I checked out both links. The comments are encouraging. The quiet through-the-wall Panasonic fan they mentioned sounds like a good one: https://www.amazon.com/Panasonic-FV-08WQ1-WhisperWall-Wall-Mounted/dp/B000MNIB9C/ref=sr_1_35?gclid=Cj0KCQjwidSWBhDdARIsAIoTVb2H4xGVRae2CMnta0BQODSXrTE7Poda7hNUCOyp6_tXClrnx4ganMcaAiBTEALw_wcB&hvadid=410016427867&hvdev=c&hvlocphy=9001952&hvnetw=g&hvqmt=e&hvrand=8077432709082551772&hvtargid=kwd-5135713304&hydadcr=7364_11107261&keywords=panasonic+whisper+green+fan&qid=1658169636&sr=8-35
I'd look into a ducted mini-split first.
To your question, yes, you can get a thermostatically controlled outlet on Amazon starting around $30. The simplest installation would be to just plug a fan into such an outlet.
The house was built in 1973 with electric baseboard heat, so there is no ductwork.
Thanks for the tip about thermostats on Amazon. I found some that you you can plug a fan (or any device) into, but I would prefer a wall-mounted thermostat that would be hard-wired to a fan built into the wall to move air from the room to the main living area when the temperature disparity between the room and the living area exceeds a certain threshold (say, 2ºF).
The device you want is called a "line voltage thermostat." They start at about $20 on Amazon.
Thank you, Nick. I am not an electrician but I think you are right about what I need. I looked up "line voltage thermostat" on Amazon and I came across this device, which I think would work except it will be a bit unsightly: https://www.amazon.com/EconoHome-Adjustable-Thermostat-Universal-Compatible/dp/B08HNHBC8P/ref=sr_1_3_sspa?
crid=1ORY3PRTZN0VO&keywords=line+voltage+thermostat&qid=1658187166&sprefix=line+voltage+thermostat%2Caps%2C133&sr=8-3-spons&psc=1&smid=A2TV6GR2NMZ11P&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFTMEhKNFNIVUNTOUUmZW5jcnlwdGVkSWQ9QTAxNzI0NDNLRTJBTk45TjZNSVomZW5jcnlwdGVkQWRJZD1BMDQwMDY0MTNLVjFYMzEwSUFUNVgmd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl
You want a SNAP DISC thermostat switch. They come in different on/off temperature settings. Look them up on AMZN.
I built some hot air solar collectors with a greenhouse fan that pushes the air through them. I believe they switch on at 90 and off at 70. There are all sorts of temperature deltas to chose from and maybe even adjustable ones. AC and easy to wire. Cost me $12.
The SNAP DISCs I found on Amazon are designed for higher temperatures (90º and up) than a home, and the 20º difference between the cut-in and cut-out temperatures is too much.
Look for a “line voltage thermostat”. They’re sometimes called “snap thermostats” or “snap switches” in the trades, but “line voltage thermostat” is the more generic name for them.
All these thermostats are is a basic thermostat, usually a mechanical one, that typically only operates to turn on a heater. Note that you can also use any regular thermostat along with a 24v transformer and and relay with a 24v AC coil to operate a fan, or pretty much anything else. The thermostat then operates the relay, and the relay can control the line voltage fan. Thermostats and control transformers are easy to get even at box stores. Grainger is a good source for relays. I like to use octal base relays and the matching sockets to make connections and any future replacements easier. You can mount the relay in a large junction box as an enclosure.
Bill
You could also put a filter on the fan to improve air quality by removing particulate.
Thanks for this suggestion! We are "buttoning up" the house, so air quality will be more of an issue.
Paul,
Apart from the fan which will be either exhausting or drawing in air into the rooms, you will also need some way to supply make-up air and equalize the pressure. That can be a grill, jumper-duct, or undercutting the doors. Because the volume of air the fan will need to blow to change the temperature in the rooms will be quite large, so will these return air openings. From a privacy and acoustical separation perspective that's a problem. Most people would prefer not to have large openings between their bedrooms and common areas.
Thanks for this valuable feedback, Malcolm. The office is on the north end of the house, so it tends to be chilly in winter. I'm thinking a fan and a passive return would gradually equilibrate the air temperature with the adjacent living area that's warmed by heat pumps. Privacy is not an issue in the office, so I think I'll experiment there and then decide whether or not to attempt the two bedrooms upstairs.
PS - We are installing inner storm windows made of 1/4" acrylic to reduce heat loss across the 49-year-old double-pane windows. See attached photo.
Paul,
The windows will no doubt make this a lot easier. The better insulated the rooms are the less differential you will see.