HVAC replacement, retrofit options

Fabrik8

Fabrik8

Overcomplicator
Joined
May 27, 2015
Location
Huntersville
A few recent threads got me thinking about this again, and the recent cold snap has got me second guessing my otherwise brilliant plan for the future.

Have a gas pack in the yard. Appears to be 2001 from the serial number decoders, and has already been repaired a few times. It's a Bryant 3.5 ton unit, gas furnace and A/C. Single zone, single thermostat. Seems to short-cycle, which is not surprising given the tonnage in Climate Zone 3. It intuitively seems like it's oversized for the house.

I've been told by HVAC people that it's at or above the expected lifespan, statistically speaking. Those people may want to sell me shiny new HVAC systems though, so maybe grain-of-salt.

House is 1880 sqft, built in 1989. 1400 first floor, 440 second floor I think. Crawlspace, encapsulated. Unconditioned attic space adjacent to 2nd floor bedroom.

All ducting for 1st floor is in crawlspace. 2nd floor ducting runs between the closets on the 1st floor, then into a junction box in the 2nd floor attic before splitting to the bedroom and bath. Duct sealing is lousy. 2nd floor is usually always hotter than 1st floor, because furnace heat rises in winter and south-facing solar heat rises in summer.


So, here's where my head is at: I need zoning. I need more than one thermostat. I need new ducts. I want to get rid of the ducts in the attic, if possible.


There's a few options I've thought of:
  1. Multi-zone mini split system(s). Maybe concealed ducted units for the 1st floor rooms, or a bigger ducted unit with multiple outlets to distribute to 1st floor rooms. Daiken makes a multi-output unit with electric dampers on each output, kinda cool. 2nd floor would get a ceiling cassette or something like that, because it's pretty well suited to that. Could remove all existing ducting in the crawlspace and attic, and replace with well-installed ducting in crawlspace as needed.
  2. Smaller gas pack for the 1st floor (prob 2.5 or 3 ton, depending on calcs), with mini-split for 2nd floor. Could remove all existing ducting in the attic. Optional replace crawlspace ducting for better quality, air sealing, and age deterioration.
  3. Shawn's idea, putting a traditional split unit in the crawlspace. Would need to keep ducting in attic space for 2nd floor, or could still use mini-split on 2nd floor only.
I haven't crunched the numbers, but I like options 1 and 2. I'm not afraid of tearing the house apart to retrofit mini-split heads inside walls or whatever needs to be done.

But, I'm apprehensive about mini-splits in cold weather as my only source of heat. I know many are rated for 100% heating down to 5 or 10 or 15 degF, but I'm skeptical of that.


Does anyone have other options, or would like to weigh in on the options above?
 
Last edited:
Per Shawn's idea, I just did some reading. Apparently you can install a furnace and air handler horizontally in a crawlspace, and can even suspend it from the joists. I knew none of this, my mind is blown. If it's suspended, I probably don't need a lift pump to get the condensate out of the house (above grade) if I get a high eff condensing furnace. Whoa.

I had zero idea that I might be able to go with a split system until now. Still would likely want a mini-split upstairs, because the packaging would be soooo easy compared to ducts in the attic and running in chases between floors.
 
Fabrik8 said:
Per Shawn's idea, I just did some reading. Apparently you can install a furnace and air handler horizontally in a crawlspace, and can even suspend it from the joists. I knew none of this, my mind is blown. If it's suspended, I probably don't need a lift pump to get the condensate out of the house (above grade) if I get a high eff condensing furnace. Whoa.

I had zero idea that I might be able to go with a split system until now. Still would likely want a mini-split upstairs, because the packaging would be soooo easy compared to ducts in the attic and running in chases between floors.
Click to expand...

Just make sure you get one that has provisions for not using crawlspace Air for combustion. I seem to remember you have a sealed crawlspace, so that means piping in fresh air and exhaust for the furnace.

What about supplementing the upstairs mini split idea with hot water baseboard? Would do this with a good HE gas water heater to help with cold temps and the mini split, or even before switching to full heat. Just check the recovery rate. Could also plumb that into first floor as well for low load heating for not much operating cost, as you are heating the water already.

Just my first quick thoughts about it.
 
3.5 tons for 1880 sq ft seems about right. A load calculation by a pro would tell you more but it sounds about appropriate from just the size of the house. I just installed a 4 ton unit on a 2067 sq ft house that is poorly insulated (116 year old house) and not efficient at all.
 
If you need a quote from a good company, call Wes at AirCentral 704 888 4371. He is a good guy and honest and does quality work.
 
Mac5005 said:
Just make sure you get one that has provisions for not using crawlspace Air for combustion. I seem to remember you have a sealed crawlspace, so that means piping in fresh air and exhaust for the furnace.

What about supplementing the upstairs mini split idea with hot water baseboard? Would do this with a good HE gas water heater to help with cold temps and the mini split, or even before switching to full heat. Just check the recovery rate. Could also plumb that into first floor as well for low load heating for not much operating cost, as you are heating the water already.

Just my first quick thoughts about it.
Click to expand...

It gets hot upstairs if the furnace is running a lot in cold weather, such as last week. That's helped along by having the second air return on the 2nd floor though, because that provides an air path for 1st floor air to rise and flow upstairs, in addition to the heat that is already provided by the upstairs ducting. That won't exist if we have a mini-split upstairs only, so the temperature should be more moderate. Basically, I'm not sure if I'm concerned about having an additional source of aux heat for the small second floor. I might just be cavalier about that though, not really knowing what to operationally expect from a mini-split from lack of experience.
 
Also, am I totally off-base for thinking that the gaspack isn't going to last forever if it's already 17-ish years old?

I just want to get ahead of the logistics of replacing it, especially if there will be a change to the system config/type as part of that replacement process. Also, spring and fall are the best times to do this, as the weather is more temperate so less discomfort.
 
Last edited:
Fabrik8 said:
Also, am I totally off-base for thinking that the gaspack isn't going to last forever if it's already 17-ish years old?

I just want to get ahead of the logistics of replacing it, especially if there will be a change to the system config/type as part of that replacement process. Also, spring and fall are the best times to do this, as the weather is more temperate so less discomfort.
Click to expand...
My parents built their house in 91 and just replaced their original gaspack/ac with a heat pump/gas unit. I doubt something built in 01 was anywhere near the quality of what was built in 91 though.
 
We just replaced a heat pump that was in the neighborhood of 17-20 years old. It was flawless up until the last couple of years, then started going down for a variety of unrelated reasons. The final straw was a major freon leak.
 
I have a mini split in the garage. I'll never buy another one. It works well but has way too many expensive electronics in it. Already had an issue that was covered under warranty. After the warranty is up, I'll be screwed.
 
broncosbybart said:
I have a mini split in the garage. I'll never buy another one. It works well but has way too many expensive electronics in it. Already had an issue that was covered under warranty. After the warranty is up, I'll be screwed.
Click to expand...
What brand is it?

We have a Sanyo in our office and I'd say it's getting close to 10yrs old. It's been pretty much trouble free from what I can remember.
 
Back
Top