Need next steps after units are dialed in

[BayshoreBandit]

Hello,

I would like to have suggestions as to what to ask of the HVAC contractor at this point.

Background:
Tampa, Florida
2 story home 3,000 sqft, 1,800 downstairs, 1,200 upstairs
Trane XL14i heat pumps, 2.5 tons one unit per floor, 9 vents per floor (returns in bedrooms and hall upstairs, single return in family room downstairs)
85 year old home, remoddled, western exposure back half gutted, new windows, insullated, sheathed 1/2" plywood, vapor barier. Eastern exposure (shaded by large oak tree) blow in insullation in walls.

Complete new HVAC installation, nothing reused from old systems.

As briefly as possible: Neither unit is able to cool adequately. Downstairs unit runs on max speed all day and is best able to achieve 77 degrees, around 2 PM unit begins to lose ground and can only hold 80 degrees until around 8 PM and then can come back down to 77. Similar upstairs but because of radiant attic heat takes until 10 pm to come back down.

A number of problems, primarily with the downstairs unit, have been resolved and both now have an 18 degree split and proper pressure at the unit. All these visits and tuning have netted one degree improvement in the downstairs possible temperature 77 verus 78.

Here are the actions taken to date (please excuse the incorrect terminology)
Replaced thermostats (honeywell 8000 series)
Increased fan speed to 450 cfm
Replaced heat exchanger in the downstairs unit
Replaced control valve (the one attached to the exchanger)
Moved the sensor on the valve from 6 o'clock to 2 o'clock position
Reduced fan speed to 400 cfm
patched two leaks in the duct work coming from the unit in to the crawlspace.

The last technican is their most skilled and he's taken this as far as he can, he said they are operating as effiently as possible and it is the combination of the heat load and leaks that some from it being an older house that is causing it not to be able to keep up.

Perhaps true but not the final resolution. What should I tell the contractor and HVAC sub next?

[BURL-REF]

Hard to say if they are undersized, but if they are running as efficient as possible, one or both could be undersized.

What sizes were the original units ?

Did the installer do a heat gain calculation & a manual D (duct size )

He installed the same size for each floor having a 600 sq ft difference between the 2.

Do both levels lose ground after 2 pm ?


If you can spare 49.95, I suggest you go here http://hvaccomputer.com/talkref.asp and get this load program. Its very simple to use and even has video help. I use it on every job and its worked well. Just double check all data input, exp walls, windows, insul r values etc. You can then compare the installers info, if he has any.

[davefr]

Did the installer do a heat gain calculation & a manual D (duct size )



That's the key question to ask the contractor.

Your home sounds like a challenge. (old, remodel, many variables)

[beenthere]

Yep, ask them what size the load calc came out to.
And what the sensible and latent loads were.
And if your units meet those loads.

They may have just guessed at size.

[dash]

Bayshore, nice area,my daughter used to have a home in South Tampa, San something was the street.

They are undersized, or not working properly,or not setup properly,hard to tell from here.

Assuming they are setup and sized properly,adding attic and crawl/floor insulation,is the best solution. Having a load calc done as is and with upgraded insulation will tell if insulation can solve the issue.

Increasing the system sizes will require increasing the duct system size as well.

The issue could also be an undersized duct system now,ask them to test the static of the duct system.

[BayshoreBandit]

Sorry I missed this in my original post.

Prior units were also 2.5 ton (14 year old 10 SEER units)

Remodelling added 200 sq ft to each floor but then you have new windows and insulation now so I figured that was a wash.

Upstairs can get to a comfortable temperature in the morning but cannot hold it once the radiant heat from the attic begins to add heat.

Downstairs can only get to 77 degrees in the morning (might be 82 outside and no sun on the house at that point). That's a big question mark in my mind because even if you wanted to be 75 it just won't get there even though there isn't much temperature differential with the outside and no radiant heat from the sun.

And to the one comment about more insulation. Attic is insulated both on the underside of roof with reflective barier and ceiling rafters with cellulose and the walls done with cellulose, crawlspace with fiberglass bat. Not much options left on that front.

As to system sizing, although this is the biggest installer in the area, their response on whether things were sized properly has been the rather annoying it wouldn't have passed inspection if it didn't pass the city load caclulation.

Thanks for the advice so far and to come.

[Gator Mouth]

I have a 2750 sf, 2-story home in Florida runs of one unit. My master bedroom is warmmer than the rest of the house, for that mater the upstairs is warmmer compared to the downstairs. I have 2 questions

1) I keep the Master Bedroom (MB) door closed at night. I have been told that if I provide a passive return from my MB to the hallway this will allow the MB to feel cooler. Since my door is shut the return air doesn't have a way to escape the room which does not allow the cold supply air into the room. Would this really help or am i just putting holes in my celing?

2) If I provide an additional supply at the top of my stairs this will keep the hot air from rising as much in my house and force more of the hot air into my return. Would this be trully benificial?

[DanW13]

With all the insulation and new windows,sounds like it's a issue of undersized units or in need of someduct remediation to be done.

[Gator Mouth]

I have a 5 ton unit and I have been up to the attic and the duct work is fine as far as installation. Nouthing is crushed the supply box is shaped fine. I do not know if the duct size is right that is beyond me, but the HVAC subcontractors that have been out to inspect all have indicated that the size was good. I don't have a humidity control on my unit which would help out tremendously for the upstairs, but I don't want to spend the money on a new unit quite yet. The one I have is only 8 years old. I was wondering if I made a few of the changes mentioned above would that help or would I be wasting my time.