HVAC dilemma

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EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
Seems like trying to get the humidity out of an unairsealed house would be darn near impossible. It seems like even a little sealing would make the job much easier.

Of course, there is 1 way of lowering relative humidity in the summer that most people don't think of. Light the woodstove!
5 kids and a dog that needs to monitor the neighborhood all the time. And one of us is home working or watching kids all the time. It’s kinda a losing battle. I’ve made some good improvements. Dehumidifier only needs dumped once a week but it was a hot summer. We Are entering that really humid and warm season where ac just runs a less so this will be a test. Humidity indoors isn’t terrible. Here is graph taken in a bedroom within 3 of the master bath door 40” off the floor.

AC482567-3D74-4D1C-8118-2371F1F67BB6.png
woodstoves here just suck in 77%RH air! December or august. Think about this, when the rest of you are putting your kettle on your stove because your house is too dry, I’m down here in the south running a dehumidifier just to dry out the wet air the stove sucks into house all winter. But at least it gives up 1000 btu s per pint! I knew it was humid here and after 11 years and looking up data I know just how humid it is.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,165
Long Island NY
But the relative humidity (not the absolute amount of water) does gor down with the stove on - because the temperature inside is going up.

(Not that that is something folks in SC would appreciate in summer....)
 

fbelec

Minister of Fire
Nov 23, 2005
3,414
Massachusetts
i would have a spray foam guy come in and spray everything he see's with open cell foam or what ever he suggests. all in one job that you don't have to do he will insulate the duct work (if it's the right size for the space) air seal the space and insulate the floor all in one swoop. job done.
 

EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
Seems like trying to get the humidity out of an unairsealed house would be darn near impossible. It seems like even a little sealing would make the job much easier.

Of course, there is 1 way of lowering relative humidity in the summer that most people don't think of. Light the woodstove!
So here is the newest information I learned today. Leakage rates increases roughly 5x if you turn on your blower and leave the front door wide open! Close that door and they increase 9x. Don’t have the source but was on an “HVAC School” podcast. I think it was an older study on existing homes. But untill this past two weeks I was oblivious to how much infiltration due to duct leakage occurs. That appliance that tries to dry out the air is actually contributing to the moisture problem. All that decreases the actual heat (sensible) that you AC can remove from your house. My three ton unit was actually only cooling at 2 tons. Probably less dirty coil leaky ducts ect.

When your dew pint is near 80 degrees that’s a lot of water you are bringing into the house. Have a slab that’s old and didn’t get a moisture barrier. That a lot of water it’s bringing into your house.

I’m trying to decide if I can live with a portable dehumidifier in the upstairs living space. It warms things up and is super noisy but only 150$. Whole house units start at 1800$ plus install.
 

EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
Sounds like this will help alot...

View attachment 298957
Too slow. I’ve got 30 feet of 20x20” Plus every register run.

I’m thinking this. It needs to last only a year or two.

 

Corey

Minister of Fire
Nov 19, 2005
2,744
Midwest
Had to turn on the old hygrometer and see the indoor humidity is running about 54% here tonight which seems fairly normal and average for summer. So doesn't see you're too far off of that.

One thing I didn't see in a quick scan of this thread - and often overlooked - is AC sizing. If you have a relatively large capacity AC in relation to the heat load, it will short cycle. By the time you build up condensation on the coil, the AC has cooled the space and already shutting down - so that humidity goes right back in the air. If you have a smaller AC, it will run longer and there will be a constant flow of condensate off the coil and you literally watch all the humidity from the house go down the drain. ...or save it up as plant and flower water. Obviously make sure your condensate drain is clear and you're getting all that water out of the house before it evaporates again.

Certainly your air sealing / insulation, etc will help with the humidity infiltration, but could actually make the humidity worse, by causing even more short cycling on the AC due to even lower heat load. People, laundry, showers, cooking, dish washing, etc can all be big sources of indoor humidity which aren't lowered by air sealing,
 

tlc1976

Minister of Fire
Oct 7, 2012
1,139
Northwest Lower Michigan
Had to turn on the old hygrometer and see the indoor humidity is running about 54% here tonight which seems fairly normal and average for summer. So doesn't see you're too far off of that.

One thing I didn't see in a quick scan of this thread - and often overlooked - is AC sizing. If you have a relatively large capacity AC in relation to the heat load, it will short cycle. By the time you build up condensation on the coil, the AC has cooled the space and already shutting down - so that humidity goes right back in the air. If you have a smaller AC, it will run longer and there will be a constant flow of condensate off the coil and you literally watch all the humidity from the house go down the drain. ...or save it up as plant and flower water. Obviously make sure your condensate drain is clear and you're getting all that water out of the house before it evaporates again.

Certainly your air sealing / insulation, etc will help with the humidity infiltration, but could actually make the humidity worse, by causing even more short cycling on the AC due to even lower heat load. People, laundry, showers, cooking, dish washing, etc can all be big sources of indoor humidity which aren't lowered by air sealing,
Excellent description of why oversizing and therefore short cycling AC is not a good idea. I never really understand why until I read this.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,165
Long Island NY
Yes. I have a slightly undersized minisplit head in my basement. It runs slowly, continuously (with the coil slightly below the dew point in its dehumidification mode). Yes it cools where I don't need it, but slow and steady works well to dehumidify. (And I don't have a heat producing, and MUCH more noisy dehumidifier running there anymore.)

In the heart of summer at 90+ degrees out there and humid sea breeze going around, I kept my below grade, 1977 basement (finished with 2x4+glassfiber+drywall, no-moisture barrier (planning on a major re-do there...)) at around 55% this way.
 

EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
Had to turn on the old hygrometer and see the indoor humidity is running about 54% here tonight which seems fairly normal and average for summer. So doesn't see you're too far off of that.

One thing I didn't see in a quick scan of this thread - and often overlooked - is AC sizing. If you have a relatively large capacity AC in relation to the heat load, it will short cycle. By the time you build up condensation on the coil, the AC has cooled the space and already shutting down - so that humidity goes right back in the air. If you have a smaller AC, it will run longer and there will be a constant flow of condensate off the coil and you literally watch all the humidity from the house go down the drain. ...or save it up as plant and flower water. Obviously make sure your condensate drain is clear and you're getting all that water out of the house before it evaporates again.

Certainly your air sealing / insulation, etc will help with the humidity infiltration, but could actually make the humidity worse, by causing even more short cycling on the AC due to even lower heat load. People, laundry, showers, cooking, dish washing, etc can all be big sources of indoor humidity which aren't lowered by air sealing,
We are probably close to correct size for cooling. Two compressor with variable speed blower with a enhanced comfort mode enabled. Without knowing coil temps I’m just guessing that it’s doing better than standard mode. Debating flipping the dips to set for 350 cfm per ton. Probably should For shoulder cooling season(keep it that way for winter so I blow less air around that just above room temp;).

Drain was plugged to start the summer. Soaked the whole inside of the unit. Coil wasn’t very clean. Cleaned that twice.

I’m guessing most of my moisture is air infiltration. It’s becoming more clear that dedicated dehumidifier. Had friends of friends leave for a month or two this summer a set the AC to 80 (we keep it at 78 untill it’s 95 then we creep up on 81) and came back to black stuff growing in their walls.

When the dew point hits 80+ we get condensation on the outside of the windows new double pane windows.

I need a blower door test and a manual J. Adding insulation will reduce cycle times. But that’s the point. Getting a decent latent load calc will be worth more than my heat gain/loss to me. With 4 total cu ft of stove in the house and decent enough cooling we won’t ever be cold in the winter and can escape to the basement in the summer m. Adding insulation really comes down how much water I need to remove with a dedicated dehumidifier. I really don’t think it’s going to be that much higher if I get my ducts sealed.

73F58EF6-5C19-48AB-8C6A-5C4246212107.jpeg
 

tlc1976

Minister of Fire
Oct 7, 2012
1,139
Northwest Lower Michigan
Yes. I have a slightly undersized minisplit head in my basement. It runs slowly, continuously (with the coil slightly below the dew point in its dehumidification mode). Yes it cools where I don't need it, but slow and steady works well to dehumidify. (And I don't have a heat producing, and MUCH more noisy dehumidifier running there anymore.)

In the heart of summer at 90+ degrees out there and humid sea breeze going around, I kept my below grade, 1977 basement (finished with 2x4+glassfiber+drywall, no-moisture barrier (planning on a major re-do there...)) at around 55% this way.
Good to see a comparison from someone who has used both. How would you compare the energy use of the minisplit to the old dehumidifier?

I run a dehumidifier in my unfinished basement. Drains to the sump pump hole. The unit says 45-50%, I haven’t checked it with an independent gauge. I might consider a minisplit sometime if the long term savings warrant it.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,165
Long Island NY
Good to see a comparison from someone who has used both. How would you compare the energy use of the minisplit to the old dehumidifier?

I run a dehumidifier in my unfinished basement. Drains to the sump pump hole. The unit says 45-50%, I haven’t checked it with an independent gauge. I might consider a minisplit sometime if the long term savings warrant it.

I unfortunately don't know the energy usage as the minisplit is hardwired and I don't have usage monitoring for that.
The stand alone unit used a decent amount, but would also add heat load coming up the stairs that the minisplit in the living room had to deal with.

I have run also with the stand alone unit at 55 pct, with the idea that the minisplit would do most of the work and the dehum. would ensure the final result. The minisplit doesn't have a hygrometer so I can't set a moisture level.

My main reason to run the minisplit is the sound. The dehum made such a fan noise. (Even when the compression was not on, to pump air so it could measure the humidity.) Now it's quiet. (And no bucket to drain.)
 

fbelec

Minister of Fire
Nov 23, 2005
3,414
Massachusetts
this conversation wouldn't have happened if yours was like this but some of the mini splits have a dehum cycle. no one sizes the things right anyway. the central air my father inlaw put in in his house was a 5 ton unit. it's a small 3 bedroom ranch. then had a unit put in in his cape cod house 2.5 tons. the house is a 5 bedroom 2 livingroom 2 fireplace 2 bath 2 level house it needed a 4 ton unit but what do i know. i just a dumb electrician. when we all go down to the cape the unit turns on at 7 am and doesn't shut down til about 11 pm and the electric bill is very large. and it never gets down below 76 in the daytime
 
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Corey

Minister of Fire
Nov 19, 2005
2,744
Midwest
We are probably close to correct size for cooling. Two compressor with variable speed blower with a enhanced comfort mode enabled. Without knowing coil temps I’m just guessing that it’s doing better than standard mode. Debating flipping the dips to set for 350 cfm per ton. Probably should For shoulder cooling season(keep it that way for winter so I blow less air around that just above room temp;).

Sounds like you have it covered on the capacity side. With two stages and variable speeds, that should adapt to a wide range of conditions.
...we keep it at 78 untill it’s 95 then we creep up on 81) and came back to black stuff growing in their walls.

When the dew point hits 80+ we get condensation on the outside of the windows new double pane windows.
I think this is a big key here. With a set point of 78-81 and dew point of 80, there is not a lot of room for actually 'conditioning' the air - ie removing the humidity. This is why your dehumidifier is effective - because it is removing humidity, but not reducing room temperature...actually adding to it some.
 
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EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
Sounds like you have it covered on the capacity side. With two stages and variable speeds, that should adapt to a wide range of conditions.

I think this is a big key here. With a set point of 78-81 and dew point of 80, there is not a lot of room for actually 'conditioning' the air - ie removing the humidity. This is why your dehumidifier is effective - because it is removing humidity, but not reducing room temperature...actually adding to it some.
Air sealing and adding insulation will tip the balance that I’m pretty close to now. But we get 4+ humid months a year where you don’t need AC that much. Then 3+ months of heat where you still need to dehumidify.

Much has been learned about how to design and install HVAC systems but my experience is. They ask you how does it run. You say ok I guess I never called you out to fix anything. And the company just replaces the old three ton unit with a new one assuming who ever did it before them did it correctly. That’s how you get a brand new two stage system installed without a fan wire or second stage heating and cooling wire because they could not even be bothered to run a new T stat wire or check that the heat strips worked. It took years for me to figure all this out. Techs coming for annual service didn’t even mention it.

Rant over. Due your due diligence. Moisture leads to mold and expensive remedies. Your hvac system probably is the most expensive system in a home you will likely buy.
 

EatenByLimestone

Super Moderator
Staff member
Agree, or they’ll upsize the furnace/boiler just a bit.

I had a 115k btu, 80% boiler in my house when I moved in. I finished off the attic and added 50% to the house size, new windows, insulation, and air sealing. I now run the house on 22k btu. I was breaking the old boiler every year due to short cycling.
 
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EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
Well we have enter southern shoulder season. Means you are comfortable outside with your shoulders exposed;) and the ac is not running enough to keep the indoor humidity in check. HPWH is doing enough to keep the basement below 60 % rh but not upstairs. Average and this is running thr AC some the last week has been 65% RH.

So this basically settles is. I’m getting a whole house dehumidifier. We have been running AC the past week not because it’s too hot but because it’s to humid. Portable dehumidifier is also running some but it’s so loud it’s obnoxious upstairs. First year I have tracked RH upstairs. I’m done with sweating as a fold laundry in a house that’s 75 degrees!

Question now is how to duct the whole house dehumidifier. Doubtful the HVAC company will have any more experience than my self. Planning on adding a dedicated return from house to unit. Then tying into a main supply for the AC with a back flow flapper. This way the AC fan does not need to run when the dehumidifier is running. Down side is adding a new return and figuring out where to place it.

On a related note had a conversation with a friend about hvac contractors in the area. He works for an energy audit company. He got a new package unit in December that was supposed to come with all new duct work. Still doesn’t have duct work done. He said no one in the area is doing any cutting edge work on remodels one outfit will only do new construction. And your choices are to over pay for sketchy on time service or just pay market rate for decent work that may or may not show up when they say they will. This whole race to the bottom for home maintenance is really not getting us anywhere. I’m willing to not go worth the lowest bid to get quality work done by a knowledgeable professional. We can’t blame this on Covid anymore. This is the American way now.

C4186E87-AF26-470F-8916-0546CDD8633D.png
 

fbelec

Minister of Fire
Nov 23, 2005
3,414
Massachusetts
careful on the unit i have done wiring for a plumber that puts them in up here and they make the place they are in warm. the brand he has put in was aprilair. he was told by the company how to size them and everytime they were installed in the basement because humidity sinks to the lowest floor because it's heavy air so it tends to be run in the basement those units running made the basement 75 to 80 degrees
 

EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
careful on the unit i have done wiring for a plumber that puts them in up here and they make the place they are in warm. the brand he has put in was aprilair. he was told by the company how to size them and everytime they were installed in the basement because humidity sinks to the lowest floor because it's heavy air so it tends to be run in the basement those units running made the basement 75 to 80 degrees
Unit will be located in a crawl space. But ducted into the supply trunk. Hopefully that spreads the hot air out. They sell split unit dehumidifiers now. Not sure I want that. You hav to pay the price of running the unit. I think I’d rather the extra heat than cold. Running the unit in the summer increases sensible cooling of the AC due to lower interior dew point by 5000 btus for every 4 degrees drop in dew point. The AC does an ok job during summer but it’s times like now through March when I really need to dry things out. I have not done the math how many btus the unit would put out. It’s probably in the 2-5k btu range. It’s a trade off I’m willing to make. Will get extra attic insulation and do some more air sealing.

Realistically it just doesn’t make cents to install a 20+ SEER variable speed unit yet. Materials cost for ducts is still really high. But I need to get it done. Insulate and add vapor barrier not ready for an encapsulated one yet. Still have flood insurance that’s listed as vented.

Humid air is actually less dense than dry air. Nitrogen is more dense than water vapor.
 

EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
Currently leaning to see if I could separate upstairs and downstairs main trunks when installing new duct this would allow for a damper and zoning with a single system or, better yet two separate systems. No idea how it would actually be done but that’s not my job.
 

vbu

Burning Hunk
Mar 3, 2019
150
MS
I'm in the same boat as you are. I have a portable unit that I keep in my shop so my tools don't start rusting. Pulled it inside last week, the unit is rated for 3500sq ft I believe. Running it wide open for a week emptying the reservoir twice a day has kept the humidity in the house right at 60%. However now with the humidity we're having now (81% as we speak, dewpoint of 69) I couldn't take it anymore and put the portable unit back in my shop. Vapor barrier is close to non existent, I guess I'll have to make that a project this winter. Just hate being down in the crawl space. What I do for now is turn the AC down to 60 degrees and let it run for about half an hour or so, so it can properly dehumidify instead of short cycling
 
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EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
I'm in the same boat as you are. I have a portable unit that I keep in my shop so my tools don't start rusting. Pulled it inside last week, the unit is rated for 3500sq ft I believe. Running it wide open for a week emptying the reservoir twice a day has kept the humidity in the house right at 60%. However now with the humidity we're having now (81% as we speak, dewpoint of 69) I couldn't take it anymore and put the portable unit back in my shop. Vapor barrier is close to non existent, I guess I'll have to make that a project this winter. Just hate being down in the crawl space. What I do for now is turn the AC down to 60 degrees and let it run for about half an hour or so, so it can properly dehumidify instead of short cycling
I sucked it up for 10 years or the heat and humidity are getting worse or now I’m mored education and have resources to remedy the humidity. I’m done dumping bucket after bucket thinking to my self wow this bucket is growing something I should bleach it but not.

It’s all rather pointless if do improve the air sealing. I’m trying. Doubtful I will get a blower door test done. This winter when it cold and I have both stoves cranking I’ll turn on all the exhaust fans and walk around with my thermal camera. Fix what I can. You can only do so much. I’ve made decent improvements inside. I’ll tackle the crawl space once all the ducts get torn out. Hopefully my hvac contractor can give me a week to get it all done. New vapor barrier floor insulation. But it’s vented and dew points in the 70s and even hitting 80 it’s just going to be damp at certain times of year.
 

fbelec

Minister of Fire
Nov 23, 2005
3,414
Massachusetts
not a 100% sure of this but let's just use round numbers. if it took a 3 ton unit to cool your house and it's running a hour to cool the house now you split the ducts and cool one floor at a time, now your ac is still 3 ton. so you have 3 ton cooling one floor instead of both floors meaning the house will be cooler and better regulated as far as temp goes but the humidity might be worse because it is on less time
 

EbS-P

Minister of Fire
Jan 19, 2019
3,511
SE North Carolina
not a 100% sure of this but let's just use round numbers. if it took a 3 ton unit to cool your house and it's running a hour to cool the house now you split the ducts and cool one floor at a time, now your ac is still 3 ton. so you have 3 ton cooling one floor instead of both floors meaning the house will be cooler and better regulated as far as temp goes but the humidity might be worse because it is on less time
Using the current package unit is not ideal. I do have a two sage compressor so In theory you could set up a damper and and on call open the damper and kick into second stage. My wife would be fine with the basement being 10 degrees colder than the rest of the house. Those living down there might not.

I’ll be getting a 100 plus pint dehumidifier so between that the AC and HPWH and a bit more sealing humidity won’t be a concern.

Ideally downstairs would get its own separate system. That’s kinda what I’m planning for. I don’t want to finish a ceiling and then tear out a big second to run more duct. It needs its own return anyway.

I could use the damper as a cheat to restrict flow during the summer to the basement. I close vents now.

I just need something done so I quit thinking about the perfect solution. Maybe someday I will get to build my dream house. But that comes with it’s own issues. (I know too much and have decent standards )
 
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vbu

Burning Hunk
Mar 3, 2019
150
MS
I just need something done so I quit thinking about the perfect solution. Maybe someday I will get to build my dream house. But that comes with it’s own issues. (I know too much and have decent standards )
This is why I'm hesitant to make big investments in the house we're currently in. But like you I'd want everything done right, and I feel like it's hard to get quality work around here. Just like my insert install, I should've just done it myself.