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Central Heat/AC: More efficient (ie: cheaper) to turn fan to constantly on?

JEDI

JEDI

Lifer
How to Make Your Air Conditioner More Effective and Efficient (lifehacker.com)

Before doing anything else, Radziej says you should check your thermostat to make sure the blower fan is on, because it helps circulate cool air, giving your AC unit a bit of a break. “Just think about it, it’s constantly circulating air from the basement up to the second floor and back down,” he told Fox 9. “It’s the most efficient way to use it.”


WHAT?!
is this true?
 
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JEDI said:
How to Make Your Air Conditioner More Effective and Efficient (lifehacker.com)

Before doing anything else, Radziej says you should check your thermostat to make sure the blower fan is on, because it helps circulate cool air, giving your AC unit a bit of a break. “Just think about it, it’s constantly circulating air from the basement up to the second floor and back down,” he told Fox 9. “It’s the most efficient way to use it.”


WHAT?!
is this true?
Click to expand...
All depends on the system, but in any case actually running the fan without the compressor side on actually ADDS heat to the space in the form of motor heat. It's small but it is a very real thing.

If it is actually taking cool air from one spot and moving it, yes it can make it feel cooler temporarily. But eventually the temperatures will equalize. It definitely doesn't make it more efficient. Efficiency is bound by energy in and energy out.
 
There is some logic in what he's saying. Air stratifies if it isn't moving, warm air up top, cooler air at the bottom.
Heating and cooling systems are often oversized as most people expect to push the button and have their home warmed/cooled in less than an hour. The problem is that oversized systems cycle a lot. Better designed systems will have longer run times that prevent stratification, but they have to be downsized for that to work.
 
Yes, I think this depends on how well your HVAC system distributes air for air conditioning. Heating distribution is fine in our house, but the temperature difference between upstairs and downstairs can be 5 degrees when the air conditioning is in use. Any additional upstairs/downstairs circulation we can get is a good thing.
 
I've read that running the fan continuously during the warmer months will increase your indoor humidity. Once the compressor kicks off, you don't want to keep the fan running as any moisture on the evaporator coil will be transferred throughout your home.

If you're not running your compressor, then turning on the furnace fan might work without affecting the indoor humidity. I've never tried it, though.
 
No, your system is not set up correctly if it is drawing in the basement air instead of air from every room through the returns.

It does not help, is less efficient, but if you have allergies this will remove more dust/etc from the air, given a good filter, and it will need changed more often.

This will also wear your motor out faster and clog the squirrel cage fan even behind a filter unless it is very good and well sealed.

Don't believe anything that's on Fox. 😉
 
I doubt most systems have returns in every room. But definitely agree the returns should be on main floors, not the basement!
 
mindless1 said:
No, your system is not set up correctly if it is drawing in the basement air instead of air from every room through the returns.

It does not help, is less efficient, but if you have allergies this will remove more dust/etc from the air, given a good filter, and it will need changed more often.

This will also wear your motor out faster and clog the squirrel cage fan even behind a filter unless it is very good and well sealed.

Don't believe anything that's on Fox. 😉
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No one said their system was drawing air out of the basement.
 
Greenman said:
No one said their system was drawing air out of the basement.
Click to expand...
Did you not read the topic starting post?
“Just think about it, it’s constantly circulating air from the basement up to the second floor and back down,”
Click to expand...

Drawing cooler air out of the basement is the only way that misguided suggestion would even make sense.
 
NutBucket said:
I doubt most systems have returns in every room. But definitely agree the returns should be on main floors, not the basement!
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They're supposed to, unless an oddball (bad) architecture of the building prevents it, except for closets and smaller bathrooms. It's necessary in order to achieve good flow to the room when the door is shut. If you have adjacent rooms without doors partitioning between them, a single return for both can work as long as it's situated far enough away from the registers, but it is cheating on the job if there's a place to put more returns and they don't.

A lifetime ago I did HVAC installs into newly built homes.
 
Yeah for the first time ever I'm gonna have to agree with @mindless1. Sorry guys he is right. If your HVAC system is properly installed the advice given in the article is total shit.

I blame Nest and their misguided attempt to introduce Airwave. It was fucking stupid from the get go but hey here we are.
 
When I coded the A/C portion of my hvac control system I had logic in there so it keeps the blower running until the return and supply air temperatures are within a few degrees of each other, basically it would use up residual "coldness" that is left in the coils. I have the same logic for heat. The problem with doing that with AC though is that because the coils are going to be wet from condensation but they are no longer being kept cold, it will cause the humidity to shoot up at the tail end of the hvac cycle making the air feel clammy. I ended up removing that logic from my coding as it made things worse instead of improving things.

Now if I wanted to be more fancy, I would setup a bunch of dampers so I can bypass the evap coil and also block the upstairs returns and only draw from the basement. Then it would continue to run but it would be drawing air from basement and bringing it upstairs. Would also want a way for the air to go back to the basement to complete the loop, so can just have louvers in the basement door, or a grate somewhere that connects back to the basement.

So in normal AC mode you would have both the basement and upstairs returns involved in the system and run the system normally, when it reaches the setpoint, the compressor would turn off, a bypass damper would flip to cut the evap coil out of the hvac, the upstairs returns would shut off and another basement one would open. You want to do this in proper order to not starve the system of air. At this point it would monitor the return temperature and keep running that way until that temp is within a few degrees of the upstairs setpoint. After this it would shut off and wait for the temp to rise enough to run the AC again.

At least this would be one way that could work. Been meaning to build out my automation stuff so it's more modular and just have yet to actually do it so lot of stuff I want to do but not in position to do any of it yet. My current setup is kind of hard coded and uses protoboards and such and a bit mickeymouse, but it has held up for almost 10 years now... how time flies. It was suppose to be a temporary thrown together setup until I can design something better.
 
mindless1 said:
They're supposed to, unless an oddball (bad) architecture of the building prevents it, except for closets and smaller bathrooms. It's necessary in order to achieve good flow to the room when the door is shut. If you have adjacent rooms without doors partitioning between them, a single return for both can work as long as it's situated far enough away from the registers, but it is cheating on the job if there's a place to put more returns and they don't.

A lifetime ago I did HVAC installs into newly built homes.
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I've never seen that done in residential construction.
 
Greenman said:
I've never seen that done in residential construction.
Click to expand...
Maybe you've only seen penny-pinching bids? Back when I did it, I didn't even do the design (duct/return routing) aspect, rather an engineer already had it worked out for that model of home. Granted, that may be difficult if not impossible on some w/o a basement but in the region I worked, just about every residential had a basement.

Better question why wouldn't that be done? It's a bad design not to. Where would you leave out returns? I can't think of a single time the thought was "well we could put a return in there but let's not."
 
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It's never done around here. I've worked on multi million dollar mansions and it wasn't done. The only code requirement is that the doors be an inch off of the finished floor, and I've never seen or heard of an inspector checking that.
Other than the odd house here and there, basements don't exist here.
 
My sister's house has returns in every room, I was surprised to see that too actually, but it's a good idea. The way the bathroom fans are setup is nice too, it goes through a HRV system so you're not losing heat when the fan is on.

If I built a house these are all things I'd want to do as well to make the house as efficient as possible. Also, 2x6 outside walls for thicker insulation, then staggered 2x4 wall (so studs don't line up with the 2x6) with more insulation. Vapour barrier, then 2x3s, then drywall. The empty space on the 2x3 side would be for electrical and such so you don't need to have so many penitrations in the vapour barrier, also when you hang pictures etc you're not piercing the vapour barrier either. This would make a rather thick wall though, but that kind of works as an advantage as you get a nice big window ledge to put plants and sport trophies. 😛 Can also do 2x2s or even 1x2s if you don't want that area to be so thick, and just avoid putting electrical on outside walls. Can have some decorative faux support beams that come down and put outlets there so the electrical can be routed on the warm side.
 
^ Don't forget the windows and doors, a modern home w/modern levels of insulation, loses more through windows & doors (and shoddy work = leaks) than through the walls and ceiling.

You'll probably need more than window ledge areas-worth of plants to replenish oxygen if you seal it up tight as can be.
 
mindless1 said:
^ Don't forget the windows and doors, a modern home w/modern levels of insulation, loses more through windows & doors (and shoddy work = leaks) than through the walls and ceiling.

You'll probably need more than window ledge areas-worth of plants to replenish oxygen if you seal it up tight as can be.
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Yeah probably want to do triple pane and make sure they are installed in a sealed manner where there is continuous seal up to the vapour barrier. Spray foam is probably best bet for that.

Ideally you would want a HRV system in a house that is well sealed as well. Best to have controlled air exchange than uncontrolled leakage. An economizer on the hvac can work too for the off seasons when you get days where the temp outside is warm but not too hot. No need to run any heat or cooling in that case other than air exchange.
 
^ Or just buy a home the size you can afford to heat and cool. Invest a boatload in efficiency and the next thing you know, you have to move and get pennies on the dollar for the extra investment.

All else equal, the 1st world is not oblivious to efficiency and the trends of mobility, have already struck a balance without extreme measures.

The best way to exercise efficiency is conservation, not "more" of anything. Same amount of insulation in a smaller house, for example, or it extends to cars, boats, toaster ovens, whatever.

Depends on the climate I suppose, in some areas extreme insulation makes more of a difference than others.
 
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Or I can just make it efficient. My goal would be to build off grid if I build. There's too much red tape trying to build in the city and the costs of living is too high, whether the house is small or big it's all the same bills more or less give or take a few $100 difference if that. May as well build something off grid where I'm generating my own energy too and eliminate most bills while I'm at it.
 
mindless1 said:
^ Or just buy a home the size you can afford to head and cool. Invest a boatload in efficiency and the next thing you know, you have to move and get pennies on the dollar for the extra investment.

All else equal, the 1st world is not oblivious to efficiency and the trends of mobility, have already struck a balance without extreme measures.

The best way to exercise efficiency is conservation, not "more" of anything. Same amount of insulation in a smaller house, for example, or it extends to cars, boats, toaster ovens, whatever.

Depends on the climate I suppose, in some areas extreme insulation makes more of a difference than others.
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I looked at a place some years back that had gone total efficiency. House was a single floor 3 and 2, yearly heating and cooling was zero. Upgrade cost was $250k above the regular remodel cost. Around a 50 year break even point, assuming it all lasted that long.
 
I'm late to this discussion. But I didn't see anyone mention that if the goal is to make your house a bit more comfortable and to run the A/C compressor a little less then the advice makes sense. But if the goal is to save MONEY then it does NOT.

Depending on the size of your house, the central fan can use between ~200-400W. In my case it is rated for 300W. That is 300W running 24/7. 7.2KWH every day. 216KWH in a month. That's in addition to the heat the motor generates, as already mentioned, that the A/C needs to remove.

I used to run the fan 24/7 during warmer months based on this advice. I did this immediately upon moving into my current house so I had no baseline for what a "normal" energy bill was. My bills were $200-220 in the summer. But a couple years later when I actually examined the actual electrical usage and started doing some math, factoring in 2 gaming PCs, appliances, etc., the total electricity usage didn't add up. But then I realized that I did not factor in the energy usage of the air handler fan. Just stopping that practice of running the fan all the time knocked ~$20 a month off my energy bill (216KWH @ $0.10/KWH in Maryland).

I have since adjusted the thermostat schedule (example below) so that it cools my house several degrees below my desired temperature early in the morning before the sun rises and outside temps rise. On most hot days my A/C doesn't turn on until the late afternoon. My wife and I are also religious with keeping our heavy blinds closed when the sun is on a particular side of the house (front of the house faces east, back faces west). Between this, the thermostat's schedule, and NOT running my central fan 24/7, my energy bill is now $140-160 during the summer.

5am - Thermostat set to 68*F (Too cold for me, but I wake up soon after this temp is set)
8am - Thermostat set to 74*F (A comfortable day time temp. The sun is just cresting over the tree line behind the houses across the street. I do not have any other trees to shade my house for the rest of the day.)
8pm - 72*F (The summer sun sets, outside temps are coming down. Also what I find comfortable for sleeping without needing a blanket)
 
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