what size home?....location?...what size is each zone?...i would move the air speed to med or 400 CFMs/ton....I would also suggest a 15 KW heat strip is oversized and will hurt your pocketbook...I would have dealer change it out to a 10 KW size...

IMO

I am in Indiana. The unit in question is in my attic for the upstairs which is around 1900 square feet. The installer came and measured all the rooms, ducts, windows, and everything else and came back with this size unit. The downstairs unit is 2 ton with 10 KW. I think he said the heat strips are in stages so they will come on 5 KW at a time but I might have been wrong on that part. I need to look in the book and see the CFM/fan speed. I have an attached garage so the downstairs that has heat is closer to 1200-1400 sq ft.

Prior to this install I had a single 3.5 ton unit with a single 10 KW heat strip but it had a damper system that allowed for a stat upstairs and one down stairs. That system was way undersized for my house. With the old system the single 10 KW was not enough. Even when the down stairs was not calling for heat, the upstairs would run around the clock if it was below 20 degrees. However the single unit was downs stairs and it had to push air a lot further then the new unit now does.

W

He seemed to think with the newer unit and the "normal" temps we have been having the last several years in Indiana it won't call for emergency heat too often.

what size was the upstairs system that you replaced?...you may be undersized on outside condenser and oversized on strip heat...was a load calculation performed?...that last statement your dealer said is nonsense...

IMO

I only had one system for the entire house. It was way undersized, it was a 3.5 ton system with a single 10K heat strip. (heating 3300 square foot, two story) One unit with a baffle system that controlled the "zones". He had a chart for Indiana, I can't remember now the exact numbers but it was something along the lines of 90% of the time in Indiana the temperature is above 20 degrees (again paraphrasing). I know last night and this morning it was below 20 degrees and the system was running with the HP only and keeping the temps stable. When I got up this morning I kicked the temps up several degrees and it went into emergency heat for one cycle but has been running with HP only since and it is in the 20's.

I am not sure what an actual "load calculation" is. All I know is he spent a couple hours in the attic measuring diameters of all the ducts, the length of each run, size of all the room, all the returns, etc. The he got with the supplier and together they told me what size I needed.

Also, along the same lines. With the fan currently set to high speed is that likely causing the air from the heat pump to cool down some or does that affect anything? I was sitting here thinking that the air might be warmer if it is not blowing as hard.

Load calculation for new home = having all the facts necessary to make a good estimation of the system size needed to cool / heat the home.

Load calculation for old home= a guess that looks smart only to those who do NOT know better. (GIGO = garbage in + garbage out)

Load calculations are figured via R values for insulation... which determines how well the home will retain heat or lose heat given the outdoor load (heat or cool) on the structure.

Windows have R values, doors have R values, walls have R values, ceilings have R values. In the case of a new home these values are easily known. In the case of an older home they are not known. They are guessed at.

It is quite easy to inflate or deflate the load on a home. It's also just as easy to make a mistake.

So after thinking about all these things, now ask yourself who is doing the load calculation? (Many cases it's someone with less than 5 years experience and if it's a salesman they may have no HVAC experience at all and could just be winging it.)

With that said a load calculation is ONLY a tool for those who KNOW how to use it.

The upstairs system is a 2.5 ton HP and 2.5 ton air handler with 15K electric aux heat. The unit in question is in my attic for the upstairs which is around 1900 square feet.

The summer design temperatures for Indiana are 90-93 degrees depending where you are located. The winter design temperatures are 0-6 degrees F.

How much insulation do you have in the attic? I am thinking the AC will struggle in the summer to keep the upper floor at 75 degrees during a hot day. I would be interested is seeing what the load calculation showed for the second floor. It would also be interesting to see the attic duct loss calculation. If your contractor did a load calculation then ask him to give you a copy.

When I got up this morning I kicked the temps up several degrees and it went into emergency heat for one cycle but has been running with HP only since and it is in the 20's.

What thermostat model do you have? You may have the type that turns on the auxiliary heat whenever the set and room temperature difference is more that 2 degrees. Do you know how the heat strip staging is controlled? Is done by the air handler control board?

The duct work in the attic may be poorly insulated and/or leaking. This could be the cause of air cooling down. I am not sure what high or medium means on air flow on your Tempstar air handler. Also are there independent settings for heating and cooling?

The installer said he felt certain that it would have enough air flow on medium but to be on the safe side he was going to leave it on high until we can confirm.

The installer should confirm air flow for heating and cooling at the time of installation. I don't like this "let's set it on high and see what happens" method.

I don't want to rush to judgement, but based on what you have described so far I question the skills of the installer. I suggest you call him back and ask him to address your concerns.

The house is insulated vey well. Our old system was able to keep the house cool as we wanted. Heating was the only issue we had.

As far as the thermostat, yes it will kick into emergency heat if the temp drops 2 degrees or if I crank it up more then 2 degrees. There is a light that shows when it is emergency heat. I kept a close eye on it the first two days because I was curious to see how often, if ever, it went into emergency heat. So far the only time it does is if I crank it up more then two degrees and when it is defrosting.

As far as the air flow the way he described it to me (and this gets back to my initial question) was that the air flow was sufficient when the blower was set to medium. What he didn't know was how much air flow is required with a 15 kw heat strip. I have a call in to ICP and am waiting to hear back from them.

The other thing I forgot to mention (as I didn't think my initial question would lead down this road). Is that the house was built and the initial HVAC was a complete mess. The ductwork was not size properly, not enough returns etc. The first three bids I got, all of them told me I needed at least a 5 ton unit, however the duct work as it was would not handle that. Every one said without completely redoing all the ductwork and some major renovations they would put a 4 ton unit and that is the best that could be done. Completely redoing all the ductwork and everything was not in the budget. This guy made the most sense to me and stated going with these two separate units he could re-use most of my duct work and add a few here and there to get proper air fllow. He even found when he was in the crawl space that none of the returns were capped. The ducts came down and then the joints where they turned to go to my furnace were open at the bottom.

A 15Kw heat strip will generate 51,182 BTUs of heat. I would think you would need 800-1000 CFM of air flow.

I am not expert on heat pumps and don't install them for a living. But I would think the air flow is set in order to achieve an air temperature. If the air flow is too low then the air handler will run hot and that becomes a long term reliability problem. If it is too high then you get a wind chill affect and will be uncomfortable.

What I would like to understand is how the heat strip staging works with your set up. Maybe one of the heat pump experts can explain how it is supposed to work.

Are are fee to call the manufacturer but they are going to tell you to speak to your installer. They don't respond to homeowners about installation questions.

Thanks, that is the core question I originally asked before we got off track. That is what he said. The manuals for the exchanger did not show what the CFM was at the different fan speeds and he didn't want it set too low to cause over heating. He said until we found out how many CFM it produces at each level he would leave it on high. He said what you said, if it produces enough CFM on medium then it would be better because of the wind chill affect. I just checked with the person I bought the equipment from and he should have an answer today.

Heard back from ICP. They stated that I needed to set my fan speed on tab 3 which would produce approximately 900 cfm, which would be sufficient for the 15 kw heat strip. That is where the installer already had it set at.