AC with single stage furnace?

[G-ZUS]

Hey Beyond,

Has anyone got AC installed on an old single stage furnace? Have gotten a few quotes to install central AC and everyone said it won't work and wanted to sell me a new furnace as well except for one guy who came out and said he can install AC on my dinosaur no problem. Any insight?

[Nufy]

Why should it matter.

AC uses the fan...not the two stages of heating...

Even if its a 2 speed fan it shouldnt matter.

(Not a HVAC guy)

[ExtraSlow]

HVAC companies are mostly shit bags who make more for markups on equipment replacement than anything else.
You don't need a new furnace.

[Tik-Tok]

The only thing about old furnaces that affect A/C installation is the size and location. I've got some funky ductwork that literally everyone noped out of when getting quotes and said I needed a newer smaller furnace to make it work. Even the most honest guy told me to keep my old furnace and forget about a/c until the old one finally dies on its own.

[ExtraSlow]

The only thing about old furnaces that affect A/C installation is the size and location. I've got some funky ductwork that literally everyone noped out of when getting quotes and said I needed a newer smaller furnace to make it work. Even the most honest guy told me to keep my old furnace and forget about a/c until the old one finally dies on its own.

In my Renfrew house I had same situation. Guy said the ductwork re-work woukd cost more than a furnace.

[G-ZUS]

HVAC companies are mostly shit bags who make more for markups on equipment replacement than anything else.
You don't need a new furnace.

I agree with that. furnace was made in 1976 and still going strong. i dont want to throw it and put a HE one that's going to break down yearly. just want AC. no duct rework needed. Had one guy give me a quote who came in highly recommended on here, need to install fan controller which isnt worth it and just get a new furnace. The one guy who said he can do AC on my furnace wants $5500 for just AC while the other came in at $3750 for the same AC paired with a new furnace for 9k.:nut:

[Darell_n]

Some older furnaces and ducting can’t provide the necessary CFM required to properly cool the house. My 1996 house was marginal when I put a/c in 20 years ago which I improved with a 4” filter box. Manufacturers are now making heat pump units with indoor coils installed above existing furnaces. Having the option of central heat pump heating and natural gas heating for backup is a great design IMO.

[sabad66]

Had 3 companies quote my place with original 80s era furnaces (only wanted it on my upstairs furnace). W&J and I think Arpi’s said nope unless you get a new furnace. Smaller owner operated company called Lendrix agreed to it. The furnace even had tiny ductwork, that wouldn’t fit the coil, but he expanded it and made it work. Not pretty nor perfect and you have to understand and agree it’s not going to work optimally/efficiently, but it’s definitely possible if you just don’t want to invest in a new furnace. No regrets in my case… I figure having a/c that works 85% well is better than no a/c at all.

[G-ZUS]

Had 3 companies quote my place with original 80s era furnaces (only wanted it on my upstairs furnace). W&J and I think Arpi’s said nope unless you get a new furnace. Smaller owner operated company called Lendrix agreed to it. The furnace even had tiny ductwork, that wouldn’t fit the coil, but he expanded it and made it work. Not pretty nor perfect and you have to understand and agree it’s not going to work optimally/efficiently, but it’s definitely possible if you just don’t want to invest in a new furnace. No regrets in my case… I figure having a/c that works 85% well is better than no a/c at all.

Thanks for that info, ill reach out to lendrix as well for a quote

[Cash Money Hoes]

I suspect your 1978 furnace does not have the R,W,G,Y,C connections at the control board (likely does not have a control board at all, it likely just has 2 wires that go to your gas valve from your thermostat). When your thermostat calls for AC to come on, the furnace blower motor needs to come on and simultaneously low voltage power is sent to your AC condenser outside to start it up. Furnaces that don't have the R, Y and C terminals on the board aren't set up to have AC added. There are retrofit relay thingy's that will work called a Y block and serve this purpose, but they are finicky and can fail so most companies won't offer these (or don't know they exist). This is likely the reason why no one has been willing to quote you on a new AC with your old furnace.

[G-ZUS]

I suspect your 1978 furnace does not have the R,W,G,Y,C connections at the control board (likely does not have a control board at all, it likely just has 2 wires that go to your gas valve from your thermostat). When your thermostat calls for AC to come on, the furnace blower motor needs to come on and simultaneously low voltage power is sent to your AC condenser outside to start it up. Furnaces that don't have the R, Y and C terminals on the board aren't set up to have AC added. There are retrofit relay thingy's that will work called a Y block and serve this purpose, but they are finicky and can fail so most companies won't offer these (or don't know they exist). This is likely the reason why no one has been willing to quote you on a new AC with your old furnace.

That explains it, one guy said i would need to replace the fan motor and put in a fan center control which is $$$ apparently and that's why he wants to sell me a new furnace. I will reach out to the one guy who can do it and see how he makes it work, as his quote was ~$1750 more

[Tik-Tok]

It's hilarious how these guys can't operate "outside the box". I hooked up an entire relay/bypass system for $30 so I could control the fan from upstairs without the thermostat, but they can't get a normal blower to come on without changing half the furnace?

[dj_rice]

I has A/C installed on a single stage furnace 2 years ago. But my furnace is somewhat newer Lennox Value Series from 2000 era I believe.

But its wired up kinda funky. Not the A/C itself but something is mixed up. My 2nd floor has a switch that turns the furnace fan on to blow cold air up from the basement. That works fine BUT my 2nd floor bathroom, if anyones taking a shower and turns on the bathroom vent fan, that also activates the furnace fan to blow up cold air from the basement. Noticed this during winter why house got cold when that shower was used. Is there a fix for this?

[bjstare]

That works fine BUT my 2nd floor bathroom, if anyones taking a shower and turns on the bathroom vent fan, that also activates the furnace fan to blow up cold air from the basement. Noticed this during winter why house got cold when that shower was used. Is there a fix for this?

That's a feature, not a bug. It helps push hot air from the second floor out of the house, and cycle cold air upstairs.

[B20EF]

That explains it, one guy said i would need to replace the fan motor and put in a fan center control which is $$$ apparently and that's why he wants to sell me a new furnace. I will reach out to the one guy who can do it and see how he makes it work, as his quote was ~$1750 more

I have a 1990's era furnace with only two wires - black/white to a new Rogers wifi thermostat. AC company installed relay box but wouldn't guarantee it would actually work with that thermostat. I had it installed in winter so had to wait to actually try it out. They can turn on the AC from outside to ensure it works but not actually trigger demand from my thermostat in winter. It didn't end up working in the spring so rather than call the company back I just bought 50 feet of HVAC 5 wire cable from Home Depot, fished it through wall and wired it up to my furnace/ thermostat myself - works perfect now.

[ThePenIsMightier]

That's a feature, not a bug. It helps push hot air from the second floor out of the house, and cycle cold air upstairs.

This.
New houses so tight that without the normal leaks, we literally have to push air that we paid to heat outside.

[sabad66]

I suspect your 1978 furnace does not have the R,W,G,Y,C connections at the control board (likely does not have a control board at all, it likely just has 2 wires that go to your gas valve from your thermostat). When your thermostat calls for AC to come on, the furnace blower motor needs to come on and simultaneously low voltage power is sent to your AC condenser outside to start it up. Furnaces that don't have the R, Y and C terminals on the board aren't set up to have AC added. There are retrofit relay thingy's that will work called a Y block and serve this purpose, but they are finicky and can fail so most companies won't offer these (or don't know they exist). This is likely the reason why no one has been willing to quote you on a new AC with your old furnace.

A workaround is to just leave the furnace blower fan on 24/7 during a/c season. This is what I opted for vs a relay switch. Electricity use isn’t as bad as people might think because you avoid those big draws of power that are needed when starting up the motor from idle.

[dj_rice]

That's a feature, not a bug. It helps push hot air from the second floor out of the house, and cycle cold air upstairs.

So its supposed to do that when someone uses the bathroom fan vent switch as well? The switch that operates only that function is separate on the outside hallway. I thought it would wired separately not together on both switches?

[bjstare]

So its supposed to do that when someone uses the bathroom fan vent switch as well? The switch that operates only that function is separate on the outside hallway. I thought it would wired separately not together on both switches?

Yes. It's called an interlock. Just read my post again, and think about it logically.

[The_Penguin]

Yes. It's called an interlock. Just read my post again, and think about it logically.

It's actually code with exhaust fans over a certain CFM rating.

[Darell_n]

Electricity use isn’t as bad as people might think because you avoid those big draws of power that are needed when starting up the motor from idle.

That’s why I let my personal vehicles idle 24/7, to avoid the bad mileage from stop and go traffic.

[sabad66]

That’s why I let my personal vehicles idle 24/7, to avoid the bad mileage from stop and go traffic.

Vehicle starter manufacturers hate this one simple trick!

[grampafunk]

We put one on our 25 year old shitbox furnace. 4 years ago. Run's great!

[spike98]

It's hilarious how these guys can't operate "outside the box". I hooked up an entire relay/bypass system for $30 so I could control the fan from upstairs without the thermostat, but they can't get a normal blower to come on without changing half the furnace?

This is because the newer generation of tradesmen are being taught with procedures instead of the fundamentals. They dont understand how they work by the basics so troubleshooting or "thinking outside the box" is difficult. They all refer to a manual that says, if this light blinks then do....else replace.

[Darell_n]

This is because the newer generation of tradesmen are being taught with procedures instead of the fundamentals. They dont understand how they work by the basics so troubleshooting or "thinking outside the box" is difficult. They all refer to a manual that says, if this light blinks then do....else replace.

You want an 'outside the box' install on your life and safety critical heating equipment? Ok then. Have at it, homeowner.

[spike98]

You want an 'outside the box' install on your life and safety critical heating equipment? Ok then. Have at it, homeowner.

Im not sure you get what i am saying. I never said redneck engineered or slapped together with duct tape. I am saying, is that many of these guys have no clue how the equipment actually works, whats needed to make it run (safely) and how to retrofit. The just right to, oh you need new.

Plus, your kind of overblowing HVAC as being "life and safety critical heating equipment". Its a furnace. Makes heat by burning natural gas. Its not rocket appliance corey.

[Darell_n]

Im not sure you get what i am saying. I never said redneck engineered or slapped together with duct tape. I am saying, is that many of these guys have no clue how the equipment actually works, whats needed to make it run (safely) and how to retrofit. The just right to, oh you need new.

Plus, your kind of overblowing HVAC as being "life and safety critical heating equipment". Its a furnace. Makes heat by burning natural gas. Its not rocket appliance corey.

A lot of guys aren’t willing to ‘fuck around and find out’. It’s a business, they exist to make money and are liable if your house blows up or the heat goes out freezing your water lines. Experimentation doesn’t fit well here.

[bjstare]

You want an 'outside the box' install on your life and safety critical heating equipment? Ok then. Have at it, homeowner.

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