Residential HVAC

As I mentioned in another thread about residential estimating, I found a partially built house in a nice neighborhood where the builder went bankrupt. The house is going to the foreclosure auction in two weeks.

I've been calling around like crazy trying to get quotes for finish carpentry, finish plumbing, kitchen cabinetry, finish electrical, concrete flatwork, garage doors, etc. I think I've got a good number to finish the house at $120,000 for the 2900 square feet.

So my question is this. I was looking at the HVAC and all the rough in work was done. The air handlers are in and they did a jamb up job. This house is two story with crawl space foundation and attic. So the downstairs air handler/ductwork is in the crawl space and the upstairs air handler/ductwork is in the attic. The downstairs air handler is a Trane [SIZE=10pt]2TEC3F36B1000AA (rated for 36,000 BTUs/3.0 Tons). The upstairs air handler is model number 2TEC3F42B1000AA (rated for 42,000 BTUs/3.5 Tons). I can't figure out why the upstairs air handler is larger than the downstairs. The upstairs is 925 square feet and the downstairs is 1980 sqaure feet. [/SIZE]Does anyone have any experience with this type of thing. Any advice would be appreciated. Is it possible that they switched the units and installed the wrong one in teh wrong place? Also, they're both factory shipped for R-22 so I may need to retrofit them for R-410. Bummer.

I'm not entirely sure why the upstairs would be larger, however, unless the upstairs is sealed off from the downstairs you would get a significant amount of flow through your stairway area. I would say that it is likely that it needs a larger unit in order to make up for those losses while the downstairs unit benefits for the exact same reason. I did a lot of HVAC stuff in college as I graduated as a ME but I have been in the civil field too long to remember everything. This is just my educated guess.

Upstairs you have a heck of a heat gain from the roof, depending on how it's insulated. I know in commercial HVAC, the upper floor always has more load than the others.

ekd said:

Upstairs you have a heck of a heat gain from the roof, depending on how it's insulated. I know in commercial HVAC, the upper floor always has more load than the others.

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Even when the upstairs is half the size? I assumed that it would have a much higher heat gain. I just thought that the smaller size would result in a smaller air handler. It may also be that they had planned to finish off the room over and use that unit to do it. That would add an additional 500 square feet.

It's really hard to say with the limited information you have. It's not just the square footage. It's the roof area, window area, orientation, etc. But from what you've told me, I guess I'm not shocked with the unit sizes.

As far as I'm concerned, a larger unit would be preferable. I've been in countless houses where you can't even sleep upstairs in the summertime it's so hot.

ekd said:

It's really hard to say with the limited information you have. It's not just the square footage. It's the roof area, window area, orientation, etc. But from what you've told me, I guess I'm not shocked with the unit sizes.
As far as I'm concerned, a larger unit would be preferable. I've been in countless houses where you can't even sleep upstairs in the summertime it's so hot.

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The only thing I'm worried about is that the unit won't run long enough to take the humidity out of the air. We're in a very humid climate. But I guess I could just put a 3 ton unit on the 3.5 ton air handler to be sure.

I've been in too many houses where you just can't get the upstairs cooled enough... it's especially bad in my current townhouse! We should think about moving the bedroom to the ground floor.

To get the different SEER ratings, a lot of time manufacturer's will "mismatch" air handlers and condensers. While it's common, unless it's a manufacturer approved mismatch they may or may not honor the warranty.

As someone else mentioned, it's much more your windows, orientation, insulation, volume, etc. than it is square footage. Do you have vaulted ceilings? A lot of windows with east/west exposure?

If you can give me some more detail about the house, I wouldn't mind running a load for you. Doesn't take that long.

Also, you can tell the people that say "I'd rather have a unit oversized anyway!" don't live in the south.

Theoretically, converting from an R-22 unit to R-410a should be a simple matter of replacing the metering device (TXV, piston, etc., most likely TXV). However, due to the higher operating pressure of R-410a, a lot of contractors are having problems with the factory joints leaking. I don't think this has been as much of an issue with Trane, but I know Lennox has had a ton of problems with their ADP coils (as they have for years).

There is my two cents. If you're in doubt, run a load.

^^Awesome. Here are the plans for the house. I definitely don't want an oversized unit. It's way too humid down here for that.

I talked to a buddy of mine that works at Trane and he said the TXV is all that needs to be replaced on the air handlers to convert them to R410. It should cost around $40 per unit. He can get me a 3 ton 14 SEER condenser for $1295 per unit. I have a family friend who said he would do the install at cost and install the condensers.

As I said above, they had planned to cool the room over with the upstairs air handler but I'm not going to finish that right now so I'd rather size the condenser for just the upstairs.

Let me know what you think and thanks a ton for the help. If you're ever in Charleston I'll buy you lots of beers and shrimps.

Scan001.PDF

Floor plan looks nice, Chuck. The master bedroom is on the main floor of my house, too. I wasn't sure how much I'd like that, but I do.

Interesting layout, chuck. I have a few questions about it.

1) Do you think you'd get tired of walking across the screen porch/sunroom every morning, or is that HVAC'd? If not, I'd absolutely hate it on chilly mornings.

2) There's no hallway bathroom for the second floor. That's all well and good for the folks in the two bedrooms with bath's, but the poor sap in the third bedroom is gonna have to tramp downstairs and use the powder room.

3) Is there a stairway to the storage above the garage?

Capt Worley PE said:

Interesting layout, chuck. I have a few questions about it.

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See responses below:

Capt Worley PE said:

1) Do you think you'd get tired of walking across the screen porch/sunroom every morning, or is that HVAC'd? If not, I'd absolutely hate it on chilly mornings.

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They are enclosed/HVACd sunrooms. I wouldn't even consider buying the place if they weren't. I am going to tile them.....if I get the place.

Capt Worley PE said:

2) There's no hallway bathroom for the second floor. That's all well and good for the folks in the two bedrooms with bath's, but the poor sap in the third bedroom is gonna have to tramp downstairs and use the powder room.

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True, there is no hall bath, however, the third bedroom also has a bathroom.

Capt Worley PE said:

3) Is there a stairway to the storage above the garage?

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Yes. The house/floorplan is definitely unique. That's a lot of why I like it. It has some really great details and isn't your typicaly cookie cutter type house. It's probably a long shot for me but I won't know until I try.

Chucktown PE said:

True, there is no hall bath, however, the third bedroom also has a bathroom.

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My bad. Didn't see the pocket doors.

Chucktown PE said:

^^Awesome. Here are the plans for the house. I definitely don't want an oversized unit. It's way too humid down here for that.
I talked to a buddy of mine that works at Trane and he said the TXV is all that needs to be replaced on the air handlers to convert them to R410. It should cost around $40 per unit. He can get me a 3 ton 14 SEER condenser for $1295 per unit. I have a family friend who said he would do the install at cost and install the condensers.

As I said above, they had planned to cool the room over with the upstairs air handler but I'm not going to finish that right now so I'd rather size the condenser for just the upstairs.

Let me know what you think and thanks a ton for the help. If you're ever in Charleston I'll buy you lots of beers and shrimps.

Scan001.PDF

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Sorry, a sick 7 month old kept me off here.

I'll look at it and get back to you.

If you have a guide or something that you can point me to I could probably do it and maybe you could review it?

Chucktown PE said:

If you have a guide or something that you can point me to I could probably do it and maybe you could review it?

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I'm getting a 33.1 MBH Sensible and 36.0 MBH Total for the upstairs only. That's probably a 3.5 ton, I'll have to check vendor data.

I'll run the bottom also.

Looking at the floor plan, in my opinion, you're better off running a third unit for the master bedroom suite. 1.) I like it colder in the bedroom, and 2.) You can use programmable stats to place the downstairs in "unoccupied" during the sleeping hours. 3.) With the configuration as it is, you're going to have drastically different loads for the main house versus the bedroom suite.

Did you check the duct work? If they have a three ton air handler, I'd venture to guess that was the plan all along.

Thanks jmbeck. I'm not sure it matters or not but the roof is silver standing seam metal. Does the 3.5 ton include the room over the garage?

As far as the downstairs goes, it looks like there is a zoned damper system. I haven't finished my investigative work but I'll report back next week when I get a chance to look again. It looks like the master is set up for its own thermostat and the main living area is set up for another. The 2TEC3F36B1000AA that is installed is a 3 ton air handler.

Chucktown PE said:

Thanks jmbeck. I'm not sure it matters or not but the roof is silver standing seam metal. Does the 3.5 ton include the room over the garage?
As far as the downstairs goes, it looks like there is a zoned damper system. I haven't finished my investigative work but I'll report back next week when I get a chance to look again. It looks like the master is set up for its own thermostat and the main living area is set up for another. The 2TEC3F36B1000AA that is installed is a 3 ton air handler.

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Does not include room over garage.

Did a little more digging on the house last weekend and there are 2 dampers installed in the system. They are honeywell 24V DC dampers. I'm assuming that they need a controller somewhere? There is also a bypass system that allows the air to recirculate if the damper to the main part of the house is closed. Any thoughts on what is needed down there.

Chucktown PE said:

Did a little more digging on the house last weekend and there are 2 dampers installed in the system. They are honeywell 24V DC dampers. I'm assuming that they need a controller somewhere? There is also a bypass system that allows the air to recirculate if the damper to the main part of the house is closed. Any thoughts on what is needed down there.

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That's a fairly common application nowadays. It basically a poor man's zoned system. Quote "Any thoughts on what is needed down there." With regards to what? Control system?