Author Topic: Is variable speed AC worth it for my small home?  (Read 745 times)

El_Viajero

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Is variable speed AC worth it for my small home?
« on: March 15, 2020, 08:19:25 AM »
If there are HVAC pros out there, I'd love a little advice. I might get a new HVAC system this year. I like the idea of a variable speed, fully modulating system. However, I live in a small townhouse (slightly over 1K sq. ft.) and I already have issues with airflow upstairs. That, coupled with the inevitability of the stack effect, makes it really hard to cool the upstairs rooms. On summer nights, I set the thermostat to 73 downstairs just so that I can make it 76 upstairs.

While I know variable speed systems offer better humidity control (I live in the South), better efficiency, and are less noisy, I'm worried that a system that normally runs at a lower speed would, given existing airflow issues, utterly fail to cool my upstairs. My understanding is that zoning is not possible in my home given that it's very small and has a central return trunk line for both the upstairs and downstairs. Given that my home is pretty small and isn't that expensive to heat and cool anyway, I'm also not totally convinced that the efficiency gains of a variable speed system will be very significant.

Are these concerns valid, or is the country full of two-story homes with variable speed HVAC systems that perform perfectly well? Maybe I'm overthinking this. I just don't want to pay an extra $2k or whatever for a variable speed system and not realize the benefits and/or end up with an HVAC system that struggles to cool the upstairs even more than my current system struggles to do the same.

If it makes a difference, this would be a heat pump system for AC and heat. I don't have gas lines here, so there's no furnace.

Fishindude

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Re: Is variable speed AC worth it for my small home?
« Reply #1 on: March 15, 2020, 08:34:31 AM »
Sounds to me like you have a ducting / distribution issues, and / or insulation issues.     Variable speed fans are nice, but I don't think that will cure the big difference between upstairs and downstairs temps.

Zette

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Re: Is variable speed AC worth it for my small home?
« Reply #2 on: March 15, 2020, 08:58:24 AM »
How many bedrooms do you need to cool?  I'm wondering if a single room unit would do the trick at night instead of trying to cool the whole house.  My father-in-law is an electrical and HVAC contractor in tropical Australia, and it seems that a wall-mounted a/c unit per room is the standard installation there instead of central air.   They look like this:  https://www.mitsubishicomfort.com/products/indoor-units/wall-mounted-heating-and-cooling/gallery

better late

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Re: Is variable speed AC worth it for my small home?
« Reply #3 on: March 15, 2020, 11:25:24 AM »
Was not impressed with variable speed that we had in our old house. Definitely did not cool the upstairs better than our first, regular a/c did. I felt like I payed a lot for a worse outcome. This was for a clown house with questionable insulation. YMMV

I love those wall mounted a/c units

Retireatee1

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Re: Is variable speed AC worth it for my small home?
« Reply #4 on: March 15, 2020, 01:33:34 PM »
I have a single unit with two zones and wish I had variable speed.  It would allow me to set one zone more than three degrees cooler than the other at night.  I can only do about three degrees, or the system will alarm on low discharge temperature.  The other advantage of variable speed might be that you can oversize your system a bit.  It still has to be sized correctly but maybe you can do, say, 3 tons instead of 2 1/2.  If the temps hit 100 outside you'll be in good shape with the extra capacity.

 

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