Central hvac for small spaces

[mike93lx]

My third floor has a guest suite with a separate hvac system. It's about 20 years old and working fine, so no imminent need for replacement.

It's a 1.5 ton a/c with a 50k gas furnace. Both wildly oversized for the space (probably 400 sq ft including the bathroom.

Other than moving to a mini split, are there any options for 1 ton cooling with 20-25k heating? The smallest I can find are 1.5 ton for cooling and 2-burner furnaces around the 40-50k mark.

If I wanted to install a mini split, could I have my hvac guy repurpose the existing lineset? It's all inside the walls, so I would stay with something oversized before running a new lineset.

 

[Jim greengo]

How about a ptec unit?

 

[mike93lx]

How about a ptec unit?

A through-wall hotel unit? No. The house is all brick and no way am I cutting holes. Just like a lineset, I'll go with over sizing before that.

If the unit failed, I'd cover a/c with a window unit and heating with a space heater, temporarily only.

Even doing a mini split wouldn't be ideal as the walls slope in near where the furnace and coil are, so there isn't a great spot to mount it.

I figure that I am stuck with a like replacement, just figured I'd ask

 

[PoorUB]

You probably will not be able to repurpose the existing AC lines as they are fairly specific on the sizes required.
Lennox has a 35K BTU, 90%+ furnace but that is the smallest I am aware of.

A mini split would do it, but make sure you get one that will run in the severe cold when you get those weird cold temp swings in the winter. You can mount a minisplit low on the wall and it will work fine as long as it is not blocked by furniture. Not the best choice, but it does work.

There are small heat pump chillers. They will heat or cool water and all you need is a small fan coil air handler. Not sure how cold they run, plus the smallest I am aware of is two ton. You would need to run water lines.

Small spaces are tough to heat and cool properly with limited equipment.

 

[mike93lx]

You probably will not be able to repurpose the existing AC lines as they are fairly specific on the sizes required.
Lennox has a 35K BTU, 90%+ furnace but that is the smallest I am aware of.

A mini split would do it, but make sure you get one that will run in the severe cold when you get those weird cold temp swings in the winter. You can mount a minisplit low on the wall and it will work fine as long as it is not blocked by furniture. Not the best choice, but it does work.

There are small heat pump chillers. They will heat or cool water and all you need is a small fan coil air handler. Not sure how cold they run, plus the smallest I am aware of is two ton. You would need to run water lines.

Small spaces are tough to heat and cool properly with limited equipment.

For the low use the system sees, I would be hard pressed to go with something 90+ just to get the sizing better. I haven't been monitoring humidity levels, but I have no perceptible problems right now.

There is enough capacity that I could likely make the adjoining attic conditioned space

 

[mike93lx]

You probably will not be able to repurpose the existing AC lines as they are fairly specific on the sizes required.

what happens when the lineset is larger than specified?

3/8 and 3/4 seems pretty standard for the sizing of my systems, so for discussion purposes, lets assume i have that. Mitsubishi specifies 1/4 and 3/8 for their 1 ton systems

12,000 BTU 19 SEER Multi-Positional Mitsubishi Mini-Split Single Zone H2i Hyper Heat Heat Pump - SVZ-KA12NAHZ

The Mitsubishi SVZ-KP12NA / SUZ-KA12NAHZ is a single-zone mini-split with an output of 12,000 BTU and an efficiency rating of 19 SEER. With its Hyper Heat integrated technology, the SVZ-KP12NA / SUZ-KA12NAHZ is an excellent choice to heat and cool any room in your home all year.

hvacdirect.com

that's a huge size difference, but what would happen? poor performance? non functioning?

 

[American Locomotive]

Big pipe =Low gas velocity = poor oil return.

Your use case is ideal for a minisplit.

 

[Davegvg]

IF you have a window you put in a window heat pump - just like an AC only unit.

 

[PoorUB]

what happens when the lineset is larger than specified?

that's a huge size difference, but what would happen? poor performance? non functioning?

Like the other post, with a larger suction line, poor oil return for one. Now if the out door unit is below the indoor it probably is not and issue.

Also, most mini splits have and electronic metering device in the outdoor unit. I would be concerned of messing up performance with too large of "liquid" line. The gas wll probeably "flash off" and you will have your cooling lost in the "liquid" line.

 

[mike93lx]

Like the other post, with a larger suction line, poor oil return for one. Now if the out door unit is below the indoor it probably is not and issue.

Also, most mini splits have and electronic metering device in the outdoor unit. I would be concerned of messing up performance with too large of "liquid" line. The gas wll probeably "flash off" and you will have your cooling lost in the "liquid" line.

Thanks.

The outdoor unit is over 25 feet below the indoor unit.

I'm going to shoot Mitsubishi tech support an email

The heating performance on these mitsu units is pretty great. I can easily cover out coldest winters with it and get rid of the furnace all together. Just exploring options for now. Hopin the system just holds out for a long time as it's just a guest suite for now

 

[NS68RT]

Carrier makes a 26k 90% furnace, but I think 1.5 ton is the smallest ac you're going to find that's not a mini split. Trane used to make a 1 ton, but for some reason it was discontinued.

The problem with mini splits is, the expansion device is in the outdoor unit, which means both of the ac lines need to insulated. A conventional ac system does not have an insulated liquid line. I would be concerned about the lines sweating in the wall.

 

[mike93lx]

Carrier makes a 26k 90% furnace, but I think 1.5 ton is the smallest ac you're going to find that's not a mini split. Trane used to make a 1 ton, but for some reason it was discontinued.

The problem with mini splits is, the expansion device is in the outdoor unit, which means both of the ac lines need to insulated. A conventional ac system does not have an insulated liquid line. I would be concerned about the lines sweating in the wall.

Ah, interesting, thanks. Well that would kill the idea then. There is no good way to rerun the lineset without punching a hole in the exterior wall, so that kills the idea. If I ended up in a position where the existing lineset had to be replaced due to a leak, I'd be willing to rip out drywall to run a new one, but I dont to do that just to resize the system

Going to a 90+ furnace would never pay back in this application.

Welcome aboard, BTW

 

[danski0224]

If the space isn't used all of the time, and if power is available, I'd consider the smallest split AC and electric heat.

Or a 2 stage heat pump. Might get enough heating capacity from a 2 ton unit, if the ductwork is adequate.

Running a mini split on the wrong lineset size is a recipe for failure.

 

[mike93lx]

If the space isn't used all of the time, and if power is available, I'd consider the smallest split AC and electric heat.

Or a 2 stage heat pump. Might get enough heating capacity from a 2 ton unit, if the ductwork is adequate.

Running a mini split on the wrong lineset size is a recipe for failure.

It's definitely infrequently used. I maintain it at 65 heating/80 cooling, unless someone is visiting, plus a separate dehumidifier.

I have gas at the existing furnace and getting a 240v electric line up there would be a PIA, so I don't see myself switching that over.

The ducting setup is simple, but it runs up along the roof deck on the south facing side, so I am sure I'm losing something there for sure. It doesn't ever struggle to hit the desired temp though

 

[Jackfre]

The best solution is the mini split. It isn’t the end of the world cutting a hole in a brick wall. It can be done neatly. Run the correct line set with the proper cover painted in whatever color makes it kinda/sorta disappear and you have the best most efficient system. I really enjoy tearing out old ductwork. I did it in the current house and got a lot of storage out of it.

 

[mike93lx]

The best solution is the mini split. It isn’t the end of the world cutting a hole in a brick wall. It can be done neatly. Run the correct line set with the proper cover painted in whatever color makes it kinda/sorta disappear and you have the best most efficient system. I really enjoy tearing out old ductwork. I did it in the current house and got a lot of storage out of it.

Cutting a hole is easy, sure. Then I have a lineset running down the exterior of my brick house, from the 3rd floor. No thanks. I hate the look of lineset running down the sides of houses and would tear out and patch the drywall on the second and first floor before doing that.

Tearing out the ductwork would gain me nothing besides even more drywalling experience.

If a mini was the only option, then it is what it is, but I can easily replace the system with a like-for-like and it will likely last another 20 years.

 

[danski0224]

There are nice lineset covers available.

 

[mike93lx]

There are nice lineset covers available.

I get that it doesn't have to look like a white downspout, but unless there are invisibility cloak lineset covers, I'm good.

 

[Tracs]

This is getting similar to a thread that is a few years old or more about running a mini split lineset up two levels and through 5 rooms and through attics because that poster wouldn't just run it on the outside of the building.

OP has the info he needs, no point anyone else trying to help.

 

[mike93lx]

This is getting similar to a thread that is a few years old or more about running a mini split lineset up two levels and through 5 rooms and through attics because that poster wouldn't just run it on the outside of the building.

OP has the info he needs, no point anyone else trying to help.

I won't be running a mini split. Not sure how that thread you referenced applies.

The space already has a ducted system that works fine. Yes, it could be made smaller, but it doesn't need to be. Not sure how a mini split is some magical solution

If I needed to run a new lineset, it would follow the same path. To the exterior wall, does through two rooms to the crawl and out. Hardly rocket surgery. Drywall is cheap and easy to patch. But regardless, I don't need a new lineset if I just use a ducted system.

Why is it so terrible to not want holes in the exterior walls nor running stuff on the exterior of the house? Both seem like pretty reasonable restrictions if the workarounds aren't onerous. What if I said I had an HOA that expressly prohibited it? Would it be OK then?

 

[PoorUB]

Mike, I get it, I don't care for the line set covers hanging on the side of the house either, and I have hung plenty of it. I probably would do the same if it were the only choice, rip out sheet rock and run the line set through the walls.