HVAC upgrade to 'zone' rooms for more comfort, add a "mini-split" system?

Melensdad

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Our master suite is on the far upstairs end of our home, long HVAC runs to that room, so it is hot in the summer and cool in the winter.

We tend to run the main HVAC unit excessively to compensate and after 27 years of dealing with this crap we are looking to do something drastic.

Looking at a mini-split unit, possibly this one? Maybe a different brand. But this type. Anyone have experience with these things?


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chowderman

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similar issue here - upstairs was difficult to cool...
when we had the HVAC (furnace&AC) replaced, I also had flow dampers installed on all main ducting legs.
this allows much better air flow balancing than just the outlet dampers.

extremely cost effective - but to your point, the split systems do work well, especially if the main system is close to capacity....
 

Melensdad

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...extremely cost effective - but to your point, the split systems do work well, especially if the main system is close to capacity....
Our system is beyond capacity in my experience. It may theoretically handle the square footage of the house. But it won't handle the heat gain via the expansive glass on the west wall.

My biggest question, at this point, is do I want to put in 1 of these units for the Master Suite and leave the rest of the house on the central HVAC.

OR, do I want to put in 2 of these units, 1 for the Master Suite and 1 for the other bedrooms. Putting in 2 units would reduce the square footage load on the central HVAC by 35-to-40%, and the cubic space load on the central HVAC by about 25-to-30%.
 

Doc

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Interesting concept. I'll be watching to see how this project goes. Our family room is at far end of house and is harder to cool. But it has a cathedral ceiling. I wonder if the unit shown above would work with a cathedral ceiling?
 

Melensdad

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Interesting concept. I'll be watching to see how this project goes. Our family room is at far end of house and is harder to cool. But it has a cathedral ceiling. I wonder if the unit shown above would work with a cathedral ceiling?
This particular unit is designed to be used in an attic space, crawl space, etc.

My master bedroom has a cathedral ceiling. Adjacent to is a walk-in closet and the master bath, the master bath also has a cathedral ceiling. All the existing ductwork to feed air into the bathroom and bedroom are located in the attic area over the closet. Our thought is that we install the unit over the closet, and feed the air through the original ducts (which obviously will be cut down from their current 50'+ length to about 4' to 6' long).
 
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EastTexFrank

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Interesting concept. I'll be watching to see how this project goes.

I'm Like Doc, I'm interested to see how this goes.

We're having hell with our a/c at the moment. Both units are less than 3-years old but the underground wiring from the 3-phase breaker box to the condensers is at least 50-years old and causing problems. Both units quit this last week and in 100° temperatures, that's not pleasant. We have a temporary fix right now and will probably have to rerun the wires next week.
 

chowderman

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see if you can locate a HVAC company that does commercial design/install. the standard residential guys may not have the talent to properly evaluate your situation.
 

tommu56

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Our master suite is on the far upstairs end of our home, long HVAC runs to that room, so it is hot in the summer and cool in the winter.

We tend to run the main HVAC unit excessively to compensate and after 27 years of dealing with this crap we are looking to do something drastic.

Looking at a mini-split unit, possibly this one? Maybe a different brand. But this type. Anyone have experience with these things?


View attachment 150871



they do make celing mount ones that look like an over sized bathroom fan if that will help your cituation


ceeling thingy
 

waybomb

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Just remember, too much refrigeration will cause the ac to not run long enough to dehumidify. It will get cool, but damp.
I'd try one in the master first. And see how the current system handles the smaller load.
 

Melensdad

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Just remember, too much refrigeration will cause the ac to not run long enough to dehumidify. It will get cool, but damp.
I'd try one in the master first. And see how the current system handles the smaller load.
Yup, it is commonly referred to as short cycling and I'm concerned about that. I'm leaning toward an exterior unit that will handle multiple zones but only buying 1 of the interior components. Honestly I don't think it will be a problem, the volume of the main floor rooms is fairly large because of high ceilings and open spaces, plus the bonus of lots of glass to catch the summer sun.
 

Melensdad

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FWIW there is a professional coming out on Tuesday. There is no way I can install one of these because I have no clue how to make a duct manifold or how to run 220v circuits. The rest of it seems pretty simple. But I also want someone to give me a real estimate on the size I need, how it might affect my main HVAC system, etc.

I know I need a new electrical line run if the exterior unit is to be installed where I think it needs to go. But if it can go somewhere else then maybe I have power close? In any case it seems like a pro is going to be needed give me the answers to try to fix this thing once and for all.

I'm leaning toward just doing the master bedroom. But I really like the idea of putting the 2 extra bedrooms & a large bath on another zone.
 
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chowderman

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re: one compressor to do multiple zone . . .
be careful - you'll like get a good sounding spiel about multi-speed compressors, etc - but they have been troublesome.
the commercial company that re-did my system will not install multiple speed / stage compressors because they require an inordinate amount of repairs, customers get right PO'd....
the interior fan unit is multi-speed for A/C but fixed speed for gas/hot air heating. that 'cools' the house faster (when it is x degrees above set point) by circulating more air, but the BTU's are the same..
 

Melensdad

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re: one compressor to do multiple zone . . .
I'm looking at 1 compressor for each zone. Equipment costs are roughly the same. Install cost is slightly more. My biggest question is actually the electrical load and getting power to the outside units. But I think I have an alternative location, and there is a line out there now that ran to our old hot tub and that line is unused, so I may already have the power I need?

So I may end up with 3 separate systems. 1 for the main body of the house/common areas. 1 for the extra bedrooms/bathroom. 1 for the master suite.

At a minimum I'll have 2. One for the master suite and one for the remainder of the house.

House should have been designed that way originally but the HVAC designer totally screwed up.
 

Melensdad

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So yesterday the HVAC guy showed up.

I had been using a company for years, but I wanted fresh eyes looking at my system, so I found this new guy. Small operation but good reputation.

Talked, walked him around, talked more, he looked more. Has some ideas. 3 ideas, in fact.

1- redo my duct runs with solid ducting, put in a few in-line fans, and let the main system do the job. Likely the cheapest option but I am unsure that the system will work well enough to compensate for solar heat gain on hot & sunny days. Still, might be a good try, for a first step.
2- zone off the master bedroom suite with the mini-split of my choice
3- zone off the whole upstairs with a mid-size traditional HVAC system

He is not a big fan of the "Mini-Split" heat pumps, especially as a primary heat source. But looking at my house, and the mini-split as a secondary heat source, he is sort-of OK with it. For AC apparently they are very very efficient. He thinks the traditional HVAC won't cost much more than a mini-split but I think there might be a big price difference.


He also checked out my compressor and found it low on freon, topped that off. Cleaned out the fins better than I ever managed to do, and then he almost electrocuted himself. Decided to check the wiring of the compressor. Found a mouse next + 2 fried mice. They chewed the wire insulation but the wires were not touching each other . . . until he started to remove the nest. FLASH BANG!!! Fortunately he was NOT touching any of the metal. I was standing 6 feet away looking right at him and the flash was so bright it made the sun on a sunny day seem dim. A few choice words later and he composed himself and pulled the breaker. I was just happy I didn't need to dig a hole out back and bury his body.

I should have a couple prices by Monday on various options.
 

Doc

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:wow: one lucky guy. Very interesting info also. thanks. :tiphat:
 

m1west

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Informative post, I have the same issues, House is insulated very well but heat and cooling doesn't distribute through the house evenly. Now I have some options
 

Melensdad

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So from what I can tell, I have about 200' of flexible ductwork in my attic.

Flex duct is cheap to run, it also offers the greatest reduction in airflow, which makes long runs very inefficient. For short runs it can be fine, like from a rigid trunk line to a vent a few feet away. But running it across the length of an attic is stupid.

The HVAC guy is strongly pushing that we replace the flex lines with insulated sheet metal ducts, he said that should dramatically help and may eliminate most or all of our issues. I don't yet have a firm proposal but I'm now leaning this direction based on what I've heard from other HVAC guys in the past about the flex duct.
 

chowderman

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with a digital anemometer you can measure the airflow at various vents and determine if there is really bad balancing in the ductwork/runs.

for example, if the vents 'downstairs' are putting out 3-4 times the velocity as upstairs, and the system does not have "issues" with keeping downstairs cool, re-balancing the system may be in order.

there's no question that the flex ducting reduces airflow over normal duct work - but I would wonder if the pitter-patter is perhaps a bit to convenient....
 

Melensdad

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...there's no question that the flex ducting reduces airflow over normal duct work - but I would wonder if the pitter-patter is perhaps a bit to convenient....
Every HVAC guy who has looked at my attic ducting over the last 2.5 decades has basically said something very similar.
 
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