excessive heat, how do you protect your house during a heat wave?

[electrolyte]

Leaving the HVAC in circulate mode is an option. Any fan running will introduce heat into the structure... something to keep in mind regardless.

This is generally not a good idea. First, when cooling, when the compressor shuts off in single speed systems, you will re-evaporate lots of water back into the air. Second, even new duct systems can leak a lot, up to 5% is a pretty good figure, I think. The more you run the fan, the more air you lose. Not only do you have that percentage losses, but induce pressure differentials from room to room and from outdoors to indoors. If you have outdoor ducts (That includes attic and crawl spaces, outside the envelope, basically.) you get inside-outside differentials. Return leaks pressurize the house which is somewhat better than leaks in the supplies which depressurize. It depends on where the return is sucking the air from. If it is a damp crawl, not so good. If you depressurize the house, you are sucking air in through any small gap anywhere. If it is hot and humid, you can have immediate condensation there and mold grows. Leaks turn the AHU into a power vent with uncontrolled intake or exhaust points. Leaving the fan on constant circulate makes it into a much more effective power vent.

Inside-outside pressure differentials are not going to happen if your system is entirely within the envelope where it should be, but you can still get room to room differentials that can pressurize and depressurize individual rooms.

Duct leaks cause dry indoor air in the winter.

 

[Poppy]

He has a mini split system. No pressure differentials, and no leakage outside.

A through the wall fan may be the answer to his question.
I used a fan that was mounted in the corner of a doorway to move heat from the kitchen to a mudroom. It was kind of loud, but could be put on a rheostat. This one may no longer be available.

 

[turbodog]

This is generally not a good idea. ...

I agree and disagree with (parts) of what you've said.

The devil's in the details...

Yes, running the HVAC in circ mode will carry water from the evap coil into the air. Depending on factors (airflow due to temp deltas, how often your unit cycles, if ducts are underfloor/attic, etc) this may or may not actually amount to anything. From running mine in circ mode for ~15 years it appears to be the latter, but I am in the deep south.

This tends to make the unit run a little more... which evens out temps as rooms get more air more of the time. This costs money of course.

And that was the thrust of the question... how to deal w/ heat wave. Now if the unit can't keep up at all... then we are talking insulation, window treatments, limiting heat-producing activities, cleaning coils, checking filters.

The circ mode comes at a cost of money, but the longer runtimes are more efficient also, and if it helps avoid hot spots, my experience has been that it's worth it. The additional airflow also tends to dry out any potential condensation in the system, thereby avoiding mold.

Many of these questions are unanswerable (unless you want to scope your ducts). But if the house feels better, then problem solved.

 

[electrolyte]

He has a mini split system. No pressure differentials, and no leakage outside.

A through the wall fan may be the answer to his question.
I used a fan that was mounted in the corner of a doorway to move heat from the kitchen to a mudroom. It was kind of loud, but could be put on a rheostat. This one may no longer be available.

Poppy, I remember seeing those doorway fans from time to time. Note that there is a safety advantage to an "official" powered jump duct of some sort. They will, almost certainly, have a fuse to shut them off in the case of a fire. I offered the duct info because constant blower was mentioned even though the poster does not have them now. In addition, to discourage putting circulation ducts in the attic or through other unconditioned space in favor of trying to put any added ducts indoors.

Note that those high wall mini split heat pumps make very good ceiling heaters in the winter if you are not well insulated, especially with raised homes with poor or no floor insulation. That is, at least partly, because as they approach their set point the blower slows way down resulting in less mixing and lots of air stratification. One way to remedy that is to put a paddle fan in the middle of the room. That problem is not with only mini splits. I rented a small raised home after moving to a new city a number of decades ago. It had conventional forced-air heating and cooling. Trouble was that both the return and supplies were in the ceiling to the attic furnace. Down low was quite cold until I put a box fan on a sturdy laundry basket right under the ceiling return in the central hallway. Blowing up the cold air made a substantial difference.

 

[jtr1962]

I run my room A/Cs in the equivalent of circ mode by having the fan on all the time. Most modern units have an "ECO" setting which turns the fan off when the compressor is off. End result of that is standing water on the evaporator fins, and mildew smell when the unit kicks back on. Leaving the fan on dries off the evaporator while the compressor is off. Yes, it probably puts little moisture back in the air, but in the scheme of things the unit removes most of the excess humidity anyway while the compressor is running.

 

[Poppy]

My brother in law is a builder/remodeler. He'll often put in two sets of registers for his forced air units. One up high, and one low. During the winter, people should close the top one, and open the bottom one for heat. And vise versa during the summer for AC.

 

[turbodog]

So many differences between north/south US in building construction, temps, humidity, length of seasons, etc.

I've got such a mosquito problem I have to run a rather large fan (on low) to keep them from flooding in when I open an outside door. I gather this is not an issue up north?

 

[Poppy]

Almost certainly not to the extent as down south, but we do have Jersey mosquitos.

Three years ago when we first moved into this house mosquitos were unbearable.

I cleared the gutters, dropped a couple of mosquito pucks into the puddle of water that forms as a result of AC condensent. The evaporator is in the attic and the drain pipes out to the gutter.
And for the final step...

 

[electrolyte]

I run my room A/Cs in the equivalent of circ ....

What I see is fan off with compressor off as you say, but I have mostly seen that they turn on the fan periodically to stir up the air so they can better sense the current air temp and find the appropriate time to cycle again. That should allow drying before growth can happen. If I am shutting a unit off, I run the fan only for a time to make sure it is dry.

Central units coolers and other refrigeration equipment will often have controls that allow setting of a "drip time". That is a period after the compressor shuts off when the temperature setting is satisfied when the fan is off. After the drip time the blower comes back on.

 

[electrolyte]

So many differences between north/south US in building construction, temps, humidity, length of seasons, etc.

Ain't that the truth. Trouble is, most of the building codes were written for more temperate conditions. Please see:

https://buildingscience.com/sites/default/files/migrate/pdf/BSI-015_Top_Ten_South.pdf

 

[electrolyte]

I've got such a mosquito problem I have to run a rather large fan (on low) to keep them from flooding in when I open an outside door. I gather this is not an issue up north?

Depends on where in the North. I grew up in central New York (Chenango County). Further Southeast on the coastal plane, you get ticks, mosquitos, and even chiggers. Further North, in the 'dacks, they have black flies and they really hurt*. We had none of that because the Summers were pretty dry. (Deer ticks did come in after I was pretty much out of there.) Even poison ivy does not survive very well. It is too cold in the winter for it.

*Black flies don't have the relatively fine mouth parts to pierce and draw blood relatively painlessly. They kinda saw a hole in your skin and lap up the blood.

 

[raggie33]

i wonder if there the same as we called horse flies

 

[electrolyte]

My brother in law is a builder/remodeler.

I've seen that done, but it seems rare, like a return in every room. It is expensive and most people probably won't appreciate how much better the system works when set up that way.

 

[electrolyte]

i wonder if there the same as we called horse flies

LOL that's the problem with common names for living things. Black flies are tiny, but larger than no-see-ums.

 

[turbodog]

I've seen that done, but it seems rare, like a return in every room. It is expensive and most people probably won't appreciate how much better the system works when set up that way.

But that's a thing also... it can make temps more even, but then your duct losses (not leakage) are higher... the actual energy it takes to create airflow in something 150' long and 6" diameter. Efficiency is a _big_ deal on something that's in use as much as HVAC is.

Given that carpet's unpopular and seemingly unlikely to return... some of the airflow issues get fixed by default due to higher door clearances with hard flooring (tile, hardwood, concrete).

 

[electrolyte]

I've got such a mosquito problem I have to run a rather large fan (on low) to keep them from flooding in when I open an outside door. I gather this is not an issue up north?

Some of the worst mosquitos that I have experiences were after a rain at Cape Henlopen State Park (Delaware shore). It rained and they were upon us. Some, maybe most, mosquito species diapause (go dormant) as eggs ready to hatch and others as pupae ready to emerge as adults. Water, sometimes water with low oxygen meaning microbes growing in it as food for the larvae, triggers their development. So-called "tree hole breeders" lay their eggs at the edge of existing accumulated standing water. After a rain the water level goes up and if the oxygen tension is low enough, the larvae emerge.

 

[orbital]

+

Some years mosquitos here are just nuts, incessant little monsters.
This year we had a historically dry Spring & very few mosquitos, really none to speak of.
never had a chance to get established, million makes a billion, billion makes a trillion ...

add: all the weeks of Canadian wildfire smoke we had, likely drove the mosquitos here south & east

 

[kaichu dento]

Some of the worst mosquitos that I have experiences were after a rain at Cape Henlopen State Park (Delaware shore).

Worst mosquitoes I've ever had to deal with have been here in Alaska, unlike the ridiculous suggestion made earlier in the thread that we don't have mosquitoes in the north. Numerous times over the years I've had to run to keep them off me, and fast walking absolutely will not work.

 

[PewPewPew]

Here's something that can help. His experiment reduced the current draw by about .4 amps But actually locating your outdoor coil in a place that's not in full sunlight would be even better. If you're stuck with the coil in a sunny location, a cheap way to shade it would be pound in a piece of PVC pipe into the ground at the correct angle and then put a patio umbrella over the coil so it's in the shade during the day. It would still allow airflow around the coil and is pretty inexpensive.

 

[turbodog]

Worst mosquitoes I've ever had to deal with have been here in Alaska, unlike the ridiculous suggestion made earlier in the thread that we don't have mosquitoes in the north. Numerous times over the years I've had to run to keep them off me, and fast walking absolutely will not work.

You just need a light powerful enough to kill them.