Temperature in basement

We have a 2 story colonial style house with a basement. Maybe 1-2' of basement is above aground.

Historically, 10 years of living here, basement has been below 70 all summer (66-68 or so).

We've always had a big santa fe Advance dehumidifier in adjacent utility room, with a duct from the santa fe into the finished space (pumping out dry air, though I don't recall how warm that air was) and an open vent cover to suck in the humid air. Again, even with this santa fe setup basement was always below 70.

In April/May 2021 we had the finished portion of basement re-finished (vinyl planks over old tile, removed pink roll insulation and wood paneling and had spray foam installed on exterior walls). Santa Fe advance died, so for May through Aug/Sept I just used a portable dehu in the finished space (emptying it every day or two). Temps remained below 70 all summer.

This spring I installed a new Santa Fe Ultra 70 compact in the utility room, with ductwork on both intake and outtake to the finished space (so that it would draw humid air in and exhaust dry air out).

In late June/early July the temps in the finished space started rising above 70 (over 75 past few days). I don't know if it's related to the very warm air coming out of the Santa Fe, or simply b/c we've have a very hot summer here in CT (though of course there have been hot summers in the past). Again, I don't recall how warm the air was coming out of the old Santa Fe, so I can't compare to the temps coming out of this unit.

For the past 3 days I've turned off the santa fe and gone back to the portable, but I still can't get it below 70. So I'm not sure if the unit is the cause, or if it just takes a lot more time for the temps to start falling.

Thanks for any comments/thoughts/suggestions as to what's going on.

 

Could be a combination of everything, tighter insulation, warmer weather, change in equipment. My basement is in the mid 60's regardless of outdoor temps or even if we run dehumidifier.

 

My basement is fairly humid and stays well below 70° because the central A/C ductwork is not insulated. I'll run the dehumidifier as needed and have noticed higher than normal humidity levels which means the unit will run longer to maintain set level causing the heat level to go up.

 

I figured it was absolutely the new equipment, but since the temp hasn't dropped in a few days after turning off the new equipment, now I'm not so sure (unless it's simply too soon to tell as perhaps it takes days and days for the temp to naturally drop in a basement once it's gotten so high?).

 

Mine is a new build. Basement is spray foamed but the floor is not finished yet (still a concrete slab). 65F in summer with AC and 71F in summer. Dehumidifier is always on in the winter and holding at 43%. Your insulated basement might be holding your temps

 

In the winter? I've never know anybody to have humidity issues during winters.

 

Couple of follow-up comments/questions:

I completely forgot about the fact that we added rock wool insulation to the ceiling, and forgot to mention that we sheetrocked the ceiling and walls (used to be wood paneling on walls and drop tile ceiling). I therefore assume that between the sheetrock, better insulation on walls and now having insulation on ceiling, it's keeping the heat in (especially stopping it from rising out of basement up into rest of the house).

That being said, again, the first summer after basement was finished, it was still nice and cool (68 or so). We didn't have the new dehumidifier pumping hot air into the room though.

Should I assume that the issue this year is definitely not only the new dehumidifier pumping hot air into the finished space, but then also the fact that the hot air has no where to go, so it just stays in the finished space (and that's why turning off the dehu for a few days doesn't reduce the temp)?

I guess the only real test is at the beginning of next summer (and assuming the temps drop in the finished space over the winter), to not use the new dehu for a while (just use the portable dehu that doesn't pump hot air) and see if the temps stay low.

Thanks for any further comments/thoughts/suggestions.

 

As noted in many posts insulation does not generate heat/cold, it just slows the migration, eventually without supplemental conditioning everything will reach equilibrium with time.

That being said, technically if no supplemental heat is added to the basement other than what comes off the dehumidifier then yes the basement could warm up.

But, a dehumidifier is not a heating appliance and I have never had one that ever put out enough heat that it would raise the temp by a measurable amount.

 

Thanks, but, as noted above, there isvery warm air coming out of the Santa Fe Ultra 70. Within 2 minutes of turning on unit just now, the air temp coming out (as measured by an ir thermometer gun) was 82.5 degrees (and I believe it would read even hotter if I checked it after a longer period of time, but I'll have to confirm that later).

To the contrary, using same ir thermo gun on portable dehu, the temp (at the air exhaust grill on top) was 70 before turning on, but was actually 68 after turning on unit for a few minutes.

I therefore think it has to be the hot air coming out of the Ultra 70 (creating heat), combined with the new insulation (retaining the heat), making my basement much warmer than in the past. Last year when we just used the portable, no warm air (no heat) was being generated, so the insulation had nothing (no hot air) to retain. Does that make sense scientifically?