Just to clarify: whenever the AC is running and cooling second floor only, zone #2, (around 500sq ft room) - temp delta is awesome, 20deg or so, even on a 100+ day. Once the main zone kicks - it is no so good anymore. This makes me think (as well as the HVAC spec I had a conversation with) that current system is just not enough for square footage. Refrigerant pressure is good, filter is clean, there is some insulation in the attic (shiny stuff on the roof) but i don't think it does much - attic is hot as hell on these 100+ days. There are vent mushrooms in the attic so I keep garage slighlty open with the attic door open to keep the air flowing. Also, any AC calculator I look at it says that for the zone I'm in and sq ft of the house I need at least 5t
Mr Cool DIY split system
- Thread starter parshisa
- Start date
JHZR2
Staff member
A 20A 240V circuit runs these systems, depending upon size of course...
I have a 9000 and an 18000 BTU system in my home. NOT in TX heat, but with decent humidity and the potential to get to 100F in the summer.
I installed one myself (the older one), and had the second installed for me, as it was going into my attic, and I didnt have a ladder tall enough.
Both work great. The losses are minimal, so the efficiency is MUCH higher than a ducted system. The air handlers arent as big obviously, so they arent going to push the same kind of flow, but that may or may not be an issue depending upon what youre trying to do.
3.5 ton is a lot of cooling, so Id recommend that you check everything out first, but after that, a DIY install is a very viable thing if you want/need to augment in certain areas. I was able to buy all US made tools, and still come out WAY ahead of the costs from the HVAC folks. HVAC contractors are mostly frauds. Their pricing generally doesnt provide an hourly rate or an estimate of time to do the work. My first install was extremely simple, and didnt even require going up a ladder - we ran the lineset through my basement. There was plenty of handwaving of that they dont know what was really involved, when it was clear as day. Every "contractor" was the same way. And all the BS about needing to keep up trucks and certifications... cry me a river. My auto repair folks keep up recovery machines, EPA certifications, HAZMAT, AND brick and mortar facilities, and charge less to do HVAC work. So try to do DIY if you can, and pick a contractor very carefully if not.
I really like the split systems, and would recommend them to anyone.
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I hope my post is not confusing. I really was trying to be helpful by providing guidance information used in FL. The criteria here is 1 ton per 500 square foot of modern home living area (round it up, example 1200 square foot = 3 tons) . Florida having a similar latitude range to much of Texas, the solar insolation (solar energy) is similar and therefore the needs are not significantly different.
The suggestions that you get your system fixed are (correct or not) just assumptions that it's not working correctly. Having lived with an undersized AC unit in my previous home, it seemed to mirror your results.
One way to view temperature management is like this: The goal is to create a temperature differential (delta T) . It takes a certain amount of energy to do so. Heating is the best way to view this. It's 0 outside and you'd like 75 inside, a 75 degree differential. How many watts or BTU of heat are required to do the job in a house your size? Would 80,000 BTU be enough? Or could you do the job with a 10,000 BTU burner on the stove? Anybody who has lived it, can tell you clearly that even 80,000 BTU will fall short, 110,000+++ will probably do it (depending on location) In fact, 2 each 80,000 wood burning stoves will be required if heating with wood.
You are looking to be able to achieve at least a 25 degree differential, and you need a certain BTU to do that quickly. That number is likely to be about or around 60,000 BTU.
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thanks a lot for the feedback. I really appreciate everyone’s suggestions.
As far as my confusion goes - that purely related to the fact that different people suggest different things regarding my unit capacity.
I guess my plan will be to have current system checked and serviced with HVAC specialist to ensure it does run as designed. In case it does, I'll likely be getting 24000 BTU Mr. Cool system (supposedly it's good for around 1,000sq ft which is couple of hundred feet more than the size of the area it will be installed at).
JHZR2
Staff member
Nobody on the internet should be telling you a capacity. The right way is with a manual J or equivalent calculation which assesses sun exposure, windows, doors, people, etc. in a consistent manner. Its likely the rules of thumb were based upon something realistic, but rigor gets you the right answer. If youre trying to cut humidity, undersizing may be better so you dont get cold, damp air. New compressors may have variable geometry or different settings that let you optimize. Your ducting and the insulation on it and around it in the paths it is routed also comes into play. That all has to be looked at in earnest.
So you have a damper system that regulates airflow to the 2 different zones? Are you positive this is working properly? 3.5 tons for that size house seems low in Texas. Builders here in St Louis put 5 tons in new homes from 2500-3500 sq ft. 87 degrees inside a new house when it is 100 outside is completely unacceptable. Do your neighbors all have similar issues (assuming this is in a subdivision of similar size/style homes)?
Yes, it does regulate the air to the second floor room (separate thermostat installed in the room), and to all of the first floor (another thermostat). As far as I can tell it does work properly (cold air flows out of the ducts where it is supposed to be flowing out depending on which zone is running).
Also, I have to make a correction to my original post - it's not 87 but 77 that it would keep the house at during 100deg days (working really really hard). I apologize for the mistake and any confusion that it created.
Just looked up my neighbors unit and it is a 3ton for 2,000sq ft house (one story) which is close to my situation but a touch more favorable - less sq ft for a ton of capacity.
Honestly this isn't bad. I believe cooling systems are designed for something like a 20-25 degree differential on the worst of days in whatever locale they're in. What's the humidity like?
FWIW an AC system doesn't "work hard". It might "work long" ie run at a high percentage of the time, but it's not working harder per se. It's either on or off. Better to have a properly sized system running at a high factor than an oversized system cycling on and off.
jeff
That is an option as well. There are solar powered attic fans that run for 500$ or so. Not sure though how effective that would be in my case.
yes, ductwork is runninG through the attic. And it is hot there.99F with 108 with heatndex today. Attic is HOT.
Concur. Make sure they're properly insulated, all joints sealed, etc. This is especially true of any return ducts up there.
Attics are always hot so no surprise there
There's some thinking now that the roof should be insulated and the attic be conditioned or semi-conditioned but I assume that's not the case here. OP described what sounded like a radiant barrier which is just to reflect some of the heat load off the surface of the roof. How much insulation above the ceiling in the attic? Pretty easy to add more.As for ventilating the attic, need to be sure there's a way for fresh air to get in as well as out. OP mentioned the mushroom vents - does it have a ridge vent? Soffit vents? If it has a way to allow natural convection to ventilate then it's probably OK as is. If not adding a fan can actually be counterproductive, drawing conditioned air out of the space into the attic.
jeff
Before you do anything I would get a guy out to size your current system. I don't think 3.5 ton is too small. Something doesn't add up. And BTW, the worse thing you can do is over-size a system.....unless you like your home cold....and muggy. Over-sized will leave the air too humid.
Too much attic ventilation is bad also. If you have balanced air flow in the attic leave it alone. Since the home was built in 2014 and nobody has painted over soffit vents you should be fine. Look at duct and tonnage of the system. The ductwork could be unbalanced. If the system is undersized the unit will not shut off and will be unable to maintain temperature. If its oversized it will short cycle and leave humidity. Neither one is good and should be fixed.
during those 110F days I've seen attic to be as hot as 110-115F. Or a regular 95 (105 with HI) days it stays around 100-105. Pretty warm I'd say
