I know there are a lot of experts out here, so I'll expose my ignorance...  ;)


We JUST moved in to our house.  I've posted all the details over the winter/spring, but a quick recap below..

2x6 construction, 1" CC foam & 5.5 batts in the cavities, 1" blue board sheathing (1/2" + OSB on bracing walls), all studs caulked, sills foamed, attic sealed with 1" CC foam then R50 blown in...

Just as we moved in, we hit an extremely hot & humid 'spell', so we turned the air on right away.  What' I'm finding is that the house is holding the temp so well, that the air only turns on every few hours.  That's a good thing, I guess, but it seems to get a little "stale" while it's not running.  We do have an HRV installed, & it was set to "low" and "summer", whatever that means.  The HVAC tech is supposed to be coming later this week for an orientation on how to operate the systems, so I'm hoping that will resolve it by changing the HRV settings.

Anyone experience this, where the house holds temp a long time & the air seems kind of stagnant?

On a somewhat unrelated note, we had the air set to 74 & it seemed too cold so I turned it back up to 76.  It was at least 6 hours before the temp got up to 76 for the air to turn back on.   At our old house, the air was running constantly just to hold the temp.  I'm actually looking forward to winter to see what our heating bills are going to be like!

Congrats on completing and moving into your house! Sounds like you did a great job and the house is performing well insulation/air sealing wise! Try switching the HRV to "med" or "high" and see if that improves... sounds like the "low" setting isn't getting enough air exchanges per hour.

Have you tried running the blower fan continuously?  Some people have told me they prefer the blower always be on to move the air around.

HRVs can also be set to run continuously. In fact, some mfgrs used to recommend that they be set to run cont.
That would reduce the stale air problems. Also, if your HRV is tied into the HVAC system, then running the HVAC cont. will also run the HRV cont. BTW, I run my HVAC fan continuously, and I like the way it keeps the air mixed.

If the issue is actually interior humidity, then the HRV will make it worse. Do you know the relative humidity inside?

thanks for all of the replies. I stopped home at lunch & I'm pretty sure it's just that I don't know how to use the HRV yet.... When I got up this morning it felt "stale", and there was a fair amount of condensation on the windows. I set the HRV to "max" & by the time I left for work it was getting better. When I came home at lunch it felt better.

I'm sure there are other HRV controls than the one they put in, but this one seems very basic - there's a dial to correspond to the outside temp. It goes up to something like 40 degrees, then just goes to "summer". There's also a switch that seems to control the fan, which has 3 settings - off, min, and max. It had been set to "min", and I changed it to "max". It seems that max keeps the HRV running constantly. I may need to keep it set there.

Wes & Alton - are you saying that you keep the furnace blower running constantly? I've heard that some people do that. I tried that at our old house, & my electric bill went up pretty significantly, so I stopped. Just curious what others have seen..

Congrats on moving into the house!
 Do you have a relative indicator for humidity in the house, possibly as part of the controls for the HRV?
The comment on condensation on the windows may indicate that you have a high humidity situation in the house. If you are in a hot spell and the AC only runs a very short time and then shuts off, you may have a unit that is much too large. A large unit gives very quick cooling response, but does not get rid of the humidity. One possibility is to use a separate dehumidifier, but this is a half baked solution on a new house. The correct solution might be to remove the existing AC and replace it with a much smaller unit.
 
Some things that help control indoor humidity:
 Make sure the shower fans are on timers with a 30 min after shower run time.
After showers squeegee the water on the shower walls and hang the bath towels outdoors.
Run the range fan on high whenever you are cooking as this releases a lot of moisture.

The fact that the house only warms 2 deg over a period of hours is great. Thank you contractor for building you a good shell to live in.

Just anecdotally, in the winter, setting my ERV to 0.3 ACH the house stays just fine. In the summer double this seems to be needed to prevent stale air in the house (when the windows are closed).

Posted By jerkylips on 07 Jul 2010 04:17 PM

.........Wes & Alton - are you saying that you keep the furnace blower running constantly? I've heard that some people do that. I tried that at our old house, & my electric bill went up pretty significantly, so I stopped. Just curious what others have seen..

In addition to kwh, this will cause your indoor humidity to be higher in the summer.  When the AC is running, the cold coil causes condensation which runs into the drain.  When the compressor stops, the coil is still wet.  With the fan running, this "humidity" goes right back into the supply air stream until the coil drys.

Bruce

Posted By eric anderson on 08 Jul 2010 09:44 AM
Congrats on moving into the house!
 Do you have a relative indicator for humidity in the house, possibly as part of the controls for the HRV?
The comment on condensation on the windows may indicate that you have a high humidity situation in the house. If you are in a hot spell and the AC only runs a very short time and then shuts off, you may have a unit that is much too large. A large unit gives very quick cooling response, but does not get rid of the humidity. One possibility is to use a separate dehumidifier, but this is a half baked solution on a new house. The correct solution might be to remove the existing AC and replace it with a much smaller unit.
 
Some things that help control indoor humidity:
 Make sure the shower fans are on timers with a 30 min after shower run time.
After showers squeegee the water on the shower walls and hang the bath towels outdoors.
Run the range fan on high whenever you are cooking as this releases a lot of moisture.

The fact that the house only warms 2 deg over a period of hours is great. Thank you contractor for building you a good shell to live in.

Just anecdotally, in the winter, setting my ERV to 0.3 ACH the house stays just fine. In the summer double this seems to be needed to prevent stale air in the house (when the windows are closed).

No relative humidity indicator - not much in the way of controls at all.  I'm wondering if a better control for the HRV would be a good idea. 

As far as the condensation, I don't know that the AC is short-cycling.  It seems to run for probably 10-15 minutes when it runs - it just doesn't run very often.  Since I changed the air exchange control to 'max', we haven't had any condensation on the windows at all, and it feels very comfortable.  The HRV blower seems to be running constantly, which is good right now anyway - "that new house smell" is getting to the wife... 

We dont' have a timer on the bath fans - never really gave that any thought.  I turn it on when I get in the shower & turn it off when I'm leaving the bathroom but I know it's not running 30 minutes.  That may be something to consider, I guess..

I'd go to the hardware store and buy a humidity meter. Low AC loads commonly leave one with high humidity and this gives a musty/stale smell.

Leaving the HRV on high for a few months makes sense too - new houses off gas various things that are better off exhausted.

Theoretically an AC that is properly sized should run 100% of the time on the hottest day of the year. If it runs less then that it is oversized.
 
My parents AC runs full out on hot sunny days. It does a great job with humidity control.
My boss has an AC that is way too large. He used to run the furnace on low so the AC ran long enough to dehumidify the house. I talked him into buying a standalone dehumidifier. The dehumidifier keeps it dry and heats up the house, and the AC keeps it cool. This is not energy efficient , but it does keep the house cool and dry and is more efficient then what he had.
 
If nothing else, buy a digital weather station with inside and outside temp and humidity sensors.
 This will give you a good idea what is happening.
These are not that expensive maybe 75$ for a reasonable one.

There are also alot of sources of moisture (and offgasing) in a new house that go away with time, concrete curing, wood and paint drying, ect.  Keeping the HRV on high for the first 6 months or so is probably smart.

Cheers,
Eric

What's the best way to ensure an HVAC Contractor sizes the AC correctly given that some newer housse are sealed so tight. Do you have to do a blower door test to get an accurate idea of the air exchanges. Humidity wise what is safe indoors...overall... I realize the bathroom immediately after a shower will be higher.

I hoping to build a house like the one talked about on this thread, but I am trying to learn from situations that occur as a result of building a tight house.