I am reluctant to tell you that mini splits will handle all of your dehumidification needs. When they reduce their capacity, the indoor coil is warmer so during low load they do not dehumidify as well.
I generally recommend fresh air along with a dehumidifier. This is because ERVs and HRVs are not very good at removing moisture. I don’t know how much humidity you have in central Texas so I don’t have any specific advice for your situation.

 

Whole house dehumidifier with outside air hook up.

 

I appreciate the feedback it can definitely get humid here in the summers.

Does anyone make a smaller unit made for closer to 1k sq ft? Most of the units I've seen start closer to 2k square feet.

Any opinion on best brand for something like this?

I've run across:

- Sante Fe Ultra70 + their controller + the fresh air powered duct
- Aprilaire 8192 (looks like this is more capacity which I probably don't need and shorter warranty)


Thanks!

 

830 sq. ft. living space and an 800 CFM vent hood?! That's crazy!

Open windows or hope the walls don't buckle when you turn on the hood.

 

Gotta go big in Texas My wife likes to cook and we happened to like this NXR vent hood that we have in our main house at a different property but that one happens to be in a huge room with make up air. We'll see how this goes probably massive over kill and I suppose I'll put in one of these mechanical vents that opens when the vent hood kicks on. Just not sure I want to spring for the fan powered one as those look pricey I suppose I can always retro-fit the fan powered on in later if I have the duct in

In all honesty it will most of the time be used in the low settings so probably no where near the full 800 CFM I hope.

If I have to sink extra money in I'm more concerned about optimizing on the fresh air/de-humidification. That said I'm already way over budget but that is the joy of always over-doing everything At least it should be a nice weekend hang out when I get it wrapped up.

 

A filtered fresh air change in 3hours on a small space like you describe is minimum. This will purge indoor pollutants and renew the oxygen for 2-3 occupants. With typical "green grass climate dew point in the 60-80^F dew points and maintaining 75^F, 50%RH, a 55^F dew point removing 2-3 lbs. of moisture per hour is needed. The occupants will also add up to a lb. of moisture per hour. During peak cooling loads, your a/c may remove 2-3 lbs. per hour. The mini-splits are difficult to adjust to remove additional moisture during all put full load conditions. The main problem is during evenings and rainy days, you high outside dew point and low/no sensible cooling loads. you a good small whole house dehumidifier with the optional filtered fresh air ventilation. The Santa Fe Ultra 70, Broan 70, Trane, Lennex units are ideal.

Another benefit is that the dehumidifier will also maintain <50%RH during times the building is unoccupied by operating the dehumidifier without the a/c.

You will need a small 8" supply duct provide filtered dry fresh air to the main rooms of structure. The under cuts of the door will all return back to the dehumidifier's return.

Good thinking on your about the fresh and dehumidifier.

Keep us posted.

Regards Teddy Bear

 

Thanks for all the advice this has been great.

Just ordered the Sante Fe Ultra 70! With their controller and the fresh air damper.

Quick follow up on ducting I basically have 3 rooms:

- bedroom
- kitchen/family room (one big room)
- bathroom (just the bathroom exhaust fan in here)

My thought is to run a 6" IN/OUT into the bedroom and 6" IN/OUT the kitchen/family room should that be ok to split the 8" INTO 2x6" ducts? (ordered some 8" x 8" x 6" duct ceiling boxes)
And I'll have the 6" fresh air input hooked through the damper (planning to tee this line with 2 powered dampers one for the fresh air and one for make up air into and independent register)

------------ fresh air damper ---> ultra 70
|
6" Wall cap ----
|
-----------vent hood controlled damper ---> independent register


(basically this will save me a wall penetration and I figure make up air use should be rare)

Let me know if that sounds like it should be ok.


Thank you!

 

Who's purchasing all this?

Who's sizing all this?

Who's installing all this?

 

Probably myself at this point.

 

So YOU sized that exhaust fan 800 CFM, 1 1/2- Ton Mitsubishi in a 850 Sq Ft walk-in box? And now a whole house dehumidifier?

What calculations did YOU use?

You do realize YOU only have 1 chance of getting this right!

 

How much outside air are you planning on bringing in?

 

Yeah not claiming this is the best planned thing here. This is a weekend place where the plans evolved as we were building it we started building a metal building [3k sq ft] (barndo) and then decided to frame out a sub-portion of that building as living space originally was just going to be bedroom/bathroom (most of the building is a big garage) so I had one mini-split for that(admittedly was probably already oversized)... Then we decided why not add a kitchen/family room to the mix and run a wall all the way across so I bought another one of the same mini-split (so yeah probably doubled down on being oversized). I did try engaging with one installer early on who was big on Mitsubishi which is the reason I went that direction but he became non-responsive and never would get back to me with details and he was telling me prices were going to go up if I waited till the wrong part of the year. With all the supply chain issues going on I figured screw it and just ordered some units. (probably not the best choice I know)

I did hire a professional installer to install the mini-splits and run the lines as well as a 3.5 ton ducted split for the garage area but they were the units I had ordered. (At this point this is a sunk investment the units are installed other than the 2 heads on the wall for the 1.5 ton units). The only unit active at the moment is the 3.5 ton unit for the garage since it is not in the space I need to sheetrock so far it seems to work very well granted I still need to insulate the building but using that to keep the pipes from freezing on days when it gets colder.

My professional installer mentioned nothing of make up air/fresh air/dehumidification and I've seen the same for other installers for family members building similar reasonably tight buildings. Seems like there are many not educated on these aspects unfortunately. I know that yeah I'm not an expert either but just trying to get a decent setup and good advice seems hard to find.


The vent hood was my wife and I figuring we liked the vent hood we have at our main larger house (also NXR) so we get the 30" version of the same thing and didn't consult anyone as to the capacity... Note that it does have several speed settings are we are unlikely to ever use it at the highest capacity. From my current house we have a mechanical make up air duct that opens when it turns on so I was figuring I'll just do the same thing also watched some videos on make up air but didn't really want to spring for the fan powered one due to those being quite expensive.

My current house spray foamed 4300 sq ft home which I had a local HVAC company design the system has fresh air intake which got me thinking of that as a concern. But I had all kinds of problems with humidity after their design during certain parts of the year and particularly in the master bath. I've had to install 2 whole house de-humidifiers one I had professionally installed and a second one for our upstairs that I ended up doing myself (frankly since I could see how it was professionally done on my other unit).

I read some things on this forum about dehumidifiers with fresh air as that was a new combo to me and given my experience with my main house a de-humidifer seemed like a good idea and retrofitting it later seems like a mess since I will be using closed cell spray foam to seal the building up. That is the main reason I'm trying to get this figured out quick before I spray foam everything. The sizing on the de-humidifier was basically buying the smallest one I saw offered that claims it can coordinate with fresh air. Also this building will be sitting empty a whole lot of the time so turning off the split units and just de-humidifying much of the time seems like a good idea to save some money since it will mostly be a weekend place.

As for fresh air requirements I see that the sante-fe docs have a table that lists the ASHRAE requirements looks like it is claiming 501-1k sqft needs something like 45-60 CFM of fresh air depending on how bedrooms are counted.


So trying to do the best under the circumstances and acting off of some experience with my prior home but I realize I've very likely over done things in a couple of ways (I seem to be good at that).

Anyways sorry for the essay there but that is how I arrived where I am now.

 

Yeah not claiming this is the best planned thing here. This is a weekend place where the plans evolved as we were building it we started building a metal building [3k sq ft] (barndo) and then decided to frame out a sub-portion of that building as living space originally was just going to be bedroom/bathroom (most of the building is a big garage) so I had one mini-split for that(admittedly was probably already oversized)... Then we decided why not add a kitchen/family room to the mix and run a wall all the way across so I bought another one of the same mini-split (so yeah probably doubled down on being oversized). I did try engaging with one installer early on who was big on Mitsubishi which is the reason I went that direction but he became non-responsive and never would get back to me with details and he was telling me prices were going to go up if I waited till the wrong part of the year. With all the supply chain issues going on I figured screw it and just ordered some units. (probably not the best choice I know)

I did hire a professional installer to install the mini-splits and run the lines as well as a 3.5 ton ducted split for the garage area but they were the units I had ordered. (At this point this is a sunk investment the units are installed other than the 2 heads on the wall for the 1.5 ton units). The only unit active at the moment is the 3.5 ton unit for the garage since it is not in the space I need to sheetrock so far it seems to work very well granted I still need to insulate the building but using that to keep the pipes from freezing on days when it gets colder.

My professional installer mentioned nothing of make up air/fresh air/dehumidification and I've seen the same for other installers for family members building similar reasonably tight buildings. Seems like there are many not educated on these aspects unfortunately. I know that yeah I'm not an expert either but just trying to get a decent setup and good advice seems hard to find.


The vent hood was my wife and I figuring we liked the vent hood we have at our main larger house (also NXR) so we get the 30" version of the same thing and didn't consult anyone as to the capacity... Note that it does have several speed settings are we are unlikely to ever use it at the highest capacity. From my current house we have a mechanical make up air duct that opens when it turns on so I was figuring I'll just do the same thing also watched some videos on make up air but didn't really want to spring for the fan powered one due to those being quite expensive.

My current house spray foamed 4300 sq ft home which I had a local HVAC company design the system has fresh air intake which got me thinking of that as a concern. But I had all kinds of problems with humidity after their design during certain parts of the year and particularly in the master bath. I've had to install 2 whole house de-humidifiers one I had professionally installed and a second one for our upstairs that I ended up doing myself (frankly since I could see how it was professionally done on my other unit).

I read some things on this forum about dehumidifiers with fresh air as that was a new combo to me and given my experience with my main house a de-humidifer seemed like a good idea and retrofitting it later seems like a mess since I will be using closed cell spray foam to seal the building up. That is the main reason I'm trying to get this figured out quick before I spray foam everything. The sizing on the de-humidifier was basically buying the smallest one I saw offered that claims it can coordinate with fresh air. Also this building will be sitting empty a whole lot of the time so turning off the split units and just de-humidifying much of the time seems like a good idea to save some money since it will mostly be a weekend place.

As for fresh air requirements I see that the sante-fe docs have a table that lists the ASHRAE requirements looks like it is claiming 501-1k sqft needs something like 45-60 CFM of fresh air depending on how bedrooms are counted.

.

Suggest an 8"fresh air inlet, a 8" return from the open space in the apartment, and a 6" return large space. Use manual dampers in all of the ducts. 6" supply to the bedroom, 6" supply to the kitchen, and a 6"supply to the large area, Again manual dampers in all ducts. Electric damper in the 8" fresh air duct. This will give you the ability to fine tune the flows as you learn how to control the spaces.

Keep us posted on the issues and how it all works.

Regards Teddy Bear

 

You can keep going down this rabbit hole or take a step back. Your choice.

Get an accurate Manual "J" Performed. You can do your own here to compare: https://www.loadcalc.net/

Being an extremely tight home due to the spray foam the April air dehumidifier with a 6" outside air hook up.

 

Thank you for the advice I'll take a look at that.

 

Thanks for the advice will let you know how it goes!