Upgrade my furnace to central air?
Posted: Thu May 28, 2020 8:32 pm
Not surprisingly I'm all over the place here. First I thought I wanted an 18k BTU mini-split heat pump for my great room. And maybe I still do. But that's $1,500 for a Mr. Cool DIY system and while that gives me an extra heat source, and avoids me having to schlep my heaviest window A/C twice a year, I started wondering what it would cost to upgrade to central air. One HVAC guy quoted me a VERY ballpark number, over the phone, of around $7,000 after I told him what my situation was. Of course this same guy also quoted me $4,500 for a single 18k BTU mini-split so obviously he is not into those because that price is whacked.
I don't necessarily want to just throw away my hot air furnace. Yeah it's old, I'm guessing 30+ years old. However, it works fine. And ever since I bought the house I noticed the sticker on it that says something like "Equipped for air conditioning." I'm not sure what would make it equipped unless it just generically would fit standard size A coils.
So I started by looking up the cost of a condenser and coil.
Here is a Goodman 4 ton unit with coil and a 50 foot line set for $2,316.95.
https://hvacdirect.com/goodman-4-ton-14 ... d1662.html
I would need a bunch of other stuff and that's why I'm posting this.
But like...probably $3,000 or less? Not including refrigerant work which I may be able to borrow some stuff from my brother in law and get that done, too. Also that's only twice the single mini-split. Seems worth a look.
So it seems I can buy what I need.
No pro is going to retrofit A/C to my old-ass furnace. And the guy who is coming tomorrow is probably going to tell me that my ducting is insufficient (too small). Yeah, for modern cooling efficiency standards. But what if I want 70s standards? I'm not redoing my ductwork. And maybe I can just retrofit A/C into my furnace as if it was 1991 or whatever. What's the difference? It's not going to be as efficient as a brand new modern system but it also won't be as expensive. The idea is it would be as functional as a period system would have been. And the Goodman system I linked above is 14 SEER which is probably still quite a bit better than a standard 30 year old system so I'm still doing better.
Fortunately I found some manuals for my furnace in the basement...on the furnace. Here are some key pieces of info. One thing my furnace is missing is the controls for A/C. And look at that - the manual says exactly what I need. Honeywell Cooling Center R8325A. That has the fan controller and talks to the thermostat.
Even better, here's one on eBay:
https://www.ebay.com/itm/New-Open-Box-H ... SwlxNeqtI1
$71, not bad. Also my furnace manual shows how to wire it all up to my existing stuff.
I would also have to run a new like 5 wire thermostat wire down but my basement is unfinished so this would be a cinch. I am not sure what else I'd have to do. I would have to cut a giant hole in the duct on top of my furnace and mount the coil inside, on top of the furnace.
Other items I'd need, listed randomly:
- Condensate pump and tubing/pipe ($47)
- Disconnect switch for the condenser ($28)
- TXV ($90, https://hvacdirect.com/goodman-3-5-to-5 ... tx5n4.html), not required but should help efficiency
- Misc electrical stuff, like, uh, 8/2 or 8/3 wire and a 40A 240V breaker, or 10/2, 10/3 and a 30A breaker. 50 ft of 10/3 is $83 at https://www.homedepot.com/p/Southwire-5 ... /202316239. Maybe I can even use 10/2, not sure
- Pad and whatever else for condenser
Here are some other thoughts.
For sizing I came up with probably in the 4.5 ton range. So then it becomes a question of 4 or 5 because there is no 4.5. Part of me wants more, but you don't want to oversize A/C systems because it can lead to short cycling and poor dehumidification (from shorter running times). So maybe 4 ton would be sufficient. I have 3.6 tons of window unit normally and the upstairs bathroom and kitchen are not really cooled and tend to be warmer than the rest of the house. So it's probably closer to 4 tons than 5 based on that. The other thing is, if my ducting really is inferior (the guy will tell me tomorrow) then perhaps I am better off on the smaller end (4 ton) to avoid other issues like evaporator freezing. I think this makes sense. It makes even more sense because the coil linked above is actually a 4-5 ton, depending on the condenser used. So it's really a 5 ton coil with a 4 ton condenser. That sounds like efficiency to me, bigger coil, higher CFM, etc.
For brand, Goodman is cheap and made in the USA. Some people bag on them but I have been watching HVAC videos for the past few years. What I have learned is the installation is more important than the brand. Since I'm controlling the install, for better or for worse, no sense in spending big bucks. The other reason not to spend big bucks is there are some seriously diminishing returns for the very cutting edge super high efficiency stuff like 20+ SEER. These units have all kinds of electronic controls, variable speed compressors and all this nonsense that is likely A) less reliable and B) more expensive to fix when it breaks. So a Goodman 14 SEER is just right for me. Single speed. Simple. Cheap and easy to get parts for.
Down the road when I need a new furnace, there's no reason some or most of this couldn't be used. Worst case I'd need a new evaporator coil to fit a different furnace. The one above is $500. Should be able to reuse the condenser outside.
I don't necessarily want to just throw away my hot air furnace. Yeah it's old, I'm guessing 30+ years old. However, it works fine. And ever since I bought the house I noticed the sticker on it that says something like "Equipped for air conditioning." I'm not sure what would make it equipped unless it just generically would fit standard size A coils.
So I started by looking up the cost of a condenser and coil.
Here is a Goodman 4 ton unit with coil and a 50 foot line set for $2,316.95.
https://hvacdirect.com/goodman-4-ton-14 ... d1662.html
I would need a bunch of other stuff and that's why I'm posting this.
But like...probably $3,000 or less? Not including refrigerant work which I may be able to borrow some stuff from my brother in law and get that done, too. Also that's only twice the single mini-split. Seems worth a look.
So it seems I can buy what I need.
No pro is going to retrofit A/C to my old-ass furnace. And the guy who is coming tomorrow is probably going to tell me that my ducting is insufficient (too small). Yeah, for modern cooling efficiency standards. But what if I want 70s standards? I'm not redoing my ductwork. And maybe I can just retrofit A/C into my furnace as if it was 1991 or whatever. What's the difference? It's not going to be as efficient as a brand new modern system but it also won't be as expensive. The idea is it would be as functional as a period system would have been. And the Goodman system I linked above is 14 SEER which is probably still quite a bit better than a standard 30 year old system so I'm still doing better.
Fortunately I found some manuals for my furnace in the basement...on the furnace. Here are some key pieces of info. One thing my furnace is missing is the controls for A/C. And look at that - the manual says exactly what I need. Honeywell Cooling Center R8325A. That has the fan controller and talks to the thermostat.
Even better, here's one on eBay:
https://www.ebay.com/itm/New-Open-Box-H ... SwlxNeqtI1
$71, not bad. Also my furnace manual shows how to wire it all up to my existing stuff.
I would also have to run a new like 5 wire thermostat wire down but my basement is unfinished so this would be a cinch. I am not sure what else I'd have to do. I would have to cut a giant hole in the duct on top of my furnace and mount the coil inside, on top of the furnace.
Other items I'd need, listed randomly:
- Condensate pump and tubing/pipe ($47)
- Disconnect switch for the condenser ($28)
- TXV ($90, https://hvacdirect.com/goodman-3-5-to-5 ... tx5n4.html), not required but should help efficiency
- Misc electrical stuff, like, uh, 8/2 or 8/3 wire and a 40A 240V breaker, or 10/2, 10/3 and a 30A breaker. 50 ft of 10/3 is $83 at https://www.homedepot.com/p/Southwire-5 ... /202316239. Maybe I can even use 10/2, not sure
- Pad and whatever else for condenser
Here are some other thoughts.
For sizing I came up with probably in the 4.5 ton range. So then it becomes a question of 4 or 5 because there is no 4.5. Part of me wants more, but you don't want to oversize A/C systems because it can lead to short cycling and poor dehumidification (from shorter running times). So maybe 4 ton would be sufficient. I have 3.6 tons of window unit normally and the upstairs bathroom and kitchen are not really cooled and tend to be warmer than the rest of the house. So it's probably closer to 4 tons than 5 based on that. The other thing is, if my ducting really is inferior (the guy will tell me tomorrow) then perhaps I am better off on the smaller end (4 ton) to avoid other issues like evaporator freezing. I think this makes sense. It makes even more sense because the coil linked above is actually a 4-5 ton, depending on the condenser used. So it's really a 5 ton coil with a 4 ton condenser. That sounds like efficiency to me, bigger coil, higher CFM, etc.
For brand, Goodman is cheap and made in the USA. Some people bag on them but I have been watching HVAC videos for the past few years. What I have learned is the installation is more important than the brand. Since I'm controlling the install, for better or for worse, no sense in spending big bucks. The other reason not to spend big bucks is there are some seriously diminishing returns for the very cutting edge super high efficiency stuff like 20+ SEER. These units have all kinds of electronic controls, variable speed compressors and all this nonsense that is likely A) less reliable and B) more expensive to fix when it breaks. So a Goodman 14 SEER is just right for me. Single speed. Simple. Cheap and easy to get parts for.
Down the road when I need a new furnace, there's no reason some or most of this couldn't be used. Worst case I'd need a new evaporator coil to fit a different furnace. The one above is $500. Should be able to reuse the condenser outside.