I think this is simple issue with a simple fix, but just wanna confirm my plan.

First floor consists of 2 living areas: main living area ("Main"), and accessory (M-I-L) apartment ("Apartment"). Single doorway separating the two - door usually kept closed.

Each area has it's own t-stat, which controls it's respective hydronic heat zone. However....

The Main t-stat controls the A/C for both areas (i.e. one zone). The Apartment stat is not connected to the A/C system.

Problem: since the door is usually closed, the Apartment gets fairly warm - often 10 deg. warmer than the Main area. Keeping the door open for a few hours somewhat evens things out - but Mama likes her privacy.

Presuming the Apartment t-stat was just never wired to the A/C system:

1. Can I just run 18/2 wire (G-fan and Y-compressor) to the air handler?

2. Do you think I'll need 18/3 - to add a R to go to the air handler transformer? (suppose I'll know that when I take the t-stat off the wall).

Since there's already wires from the Apartment t-stat down into the basement, fishing should be easy. Just wanted to think this out loud with y'all.

Thanx!! Wally

 

Do you have two completely separate A/C systems.... two outside compressors and two inside air handlers ?

My guess is you only have one A/C system which means only one thermostat can control it.

 

Ahh...I didn't know that. I suppose that's why only one of the t-stats is wired to it (only 1 system). I (ignorantly) thought I could wire them both to it, and it would come on when either of them called for cooling.

See, this is why smart DIY'ers come here first...

Thanx!

 

Yes.... technically you could have two thermostats controlling one A/C unit but if either was calling for cool.... both areas would get colder. (not quite helpful)

 

Connecting 2 thermostats to a single air conditioner can often result in a back feeding issue, through the G terminal, that can cause ice to build up on the indoor coil.


Does the main thermostat have a C wire?

The Honeywell VisionPro TH8110R would allow you to add a wireless sensor and take an average reading of both areas to control cooling.

 

Yup, I see your point. If the Apartment cools to 76 deg - then the Main area will go far below that (brrrrrrr.....).

'Suppose Mama's gonna have to sweat a little.

I wonder if I can do a little creative dampering / ducting...hmmm...

Thanx again!

 

Adding a return air duct might be something to look into.

 

Sorry Houston - just saw your reply...

Not sure if it has the C wire. Still working this issue in my head (actually, for 10 years now..LOL). haven't pulled the Apartment t-stat off the wall.

Definitely will look into that VisionPro! Sounds like the perfect solution.

Thanx!!

 

A solution.... but not the perfect one. It will still be a compromise.

The ducting solution would be closer to what you want.

 

Yup - both areas have their own returns.

 

I didn't mention this - 'cause I (incorrectly) thought this was an easy fix - but here's the main problem (i.e. reason why the Apartment gets so warm):

The Main living area is 2-story, but the Apartment is 1-story, with an almost-flat roof (i.e. there's no 2nd floor to 'shield' it from the sun. Plus, the Apartment has a sliding glass door that the sun blasts through in the afternoon. I tried the radiant-block film on the glass - didn't make much difference.

 

Then you may need some more supply into that apartment.

 

This is an excellent discussion, and EXACTLY why I love this forum.

I have many more thoughts / questions, and want to continue - but since we've (more or less) resolved my initial topic, I suppose I should start a new thread. It'll be something like "Adding cooling to accessory apartment"...so if y'all could look for it, we can continue. I'll start it shortly.

Thanx again to all!! Wally

 

This is a continuation of a discussion I started in another thread. Essentially, I'm trying to increase the cooling in an accessory apartment. Background:

Modular home, built 2005. Oil / Hydronic heat, central A/C. This discussion really only concerns the first floor A/C (3 ton Heil):

First floor consists of: main living area ("Main") approx 1100 sqft, and attached accessory (M-I-L) apartment ("Apartment") approx 650 sqft. Separated by single door.

Each area has it's own t-stat for their respective heating zones, however, the A/C is one zone controlled by the t-stat in the Main area.

Main area is fed by 7 branches, either 6" or 7" flex-duct. Apartment is fed by 4 branches, same size flex-ducts. Both areas have their own returns.

Problem: Apartment gets significantly warmer than the Main area. Main t-stat set to 76 deg. and A/C does a reasonable job of maintaining that. Apartment can get as high as 85 deg. in the late afternoon. Reasons: Apartment is mostly 1 story (i.e. no 2nd floor to shield it from the sun) - with a fairly flat roof (I think 2/12, and no venting for crawl space above). Plus, there's a sliding glass door which gets blasted by the afternoon sun.

I have applied radiant-blocking film to the sliding glass door (not much help), and I think adding some gable-end venting to the crawl space above to get rid of some of the trapped heat may help.

From the previous thread, we determined the single A/C zone can only be controlled by one t-stat, so "linking" the t-stats needs more investgation.

We also mentioned somehow adding 'flow' to the Apartment, but I have some concerns:

1. Should I increase the flex-duct diameter (10"??).
2. Should I add another branch(es) to the apartment?
3. Will I need to increase the return diameter (for proper balance)?
4. Will the 3 ton unit be able to provide the increased flow?

Good discussion. Thoughts anyone?

Wally

 

Wally... no thoughts at the moment but I combined your threads into a single topic. Flows better and keeps all the ideas in a single place.

 

Agreed...makes sense. Thanx.