Is my HVAC Guy correct? 2 systems instead of 1 system with Dampers

I'll soon be working on converting a second floor of a residential building that was never finished and is being used as an attic for the last 80+ years. Building Size 36'x36', 9 1/2' 1st floor ceiling height, 8' planned ceiling height in 2nd floor with plenty of insulation and air barrier planned.  This is also a DayCare Facility.

I will be adding an open stairway to the floor plan to provide access to the 2nd floor. (Clients request for capitalizing on the natural daylighting.)

The HVAC guy informed me that: having 2 separate HVAC systems is the route he would use because-it was how he learned and is the norm in St Louis:

  • Existing HVAC system for  1st floor is undersized 1 1/2 Ton compressor should be 3 Ton unit. (located in the Basement)
  • 1 system with dampers for climate control could  lead to future mechanical problems if one big system was used.  (I don't believe he had faith in a damper system to work over long periods of time.)
  • Controlling Costs and Not disrupting existing downstairs.  We would have to build a chase for the hvac ducts from the basement to the 2nd floor. (closet space is available to do this)

The RED warning light that is going off in my head and is contrary to all I've learned is that: "What will keep one system from robbing the climatized air from the other system?"  The open stairway will allow air movement up and down.

I agree with him partially on 2 systems if there was not an open stairway planned.

Since this is in design stages to capture the natural lighting I've mentioned a French door with a wall would allow lighting and separate the floors.  Which makes a dual system more appealing to me.

Thanks in advance for any advice.

Build Green,


The following CAD drawings were made using Sketchup and what I've found is an easy way to convert plans into picture files for showing my clients what the finished product will look like.  Yes there will be rails on the stairs, omitted so that it doesn't clutter up the drawing.

Instead of this railing set up a wall with a French door would allow the natural light into the room.  And also alleviate my fears of a child climbing the rails and falling to the 1st floor.  If this design is chosen I plan to build the railing 48" tall.

Tags: Air, Energy, HVAC, Movement, Split, Systems

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Since publishing this article I've already fired the original hvac person because he could not supply a bid on time. 

I plan to use the old pro who generally handles my hvac work.  He also mentioned the same thing as you did Mr Blanchette.  

I'll inquire about this and see if this was his reasoning for his suggestion as well as discussing the clean air aspects mentioned by Mr Kinder.

Thank you for your advice and suggestions.


thank you. Scotty

Ted Kid,

Thank you for sharing your thoughts.


Ted, stop "beating around the bush" and tell him like it is :))


How old is the existing system?  Is this a heat pump since you only talk tons or is it a furnace / AC?  You are in St. Louis so CZ 4  Mixed Humid. 

What else do you know about the existing enclosure?  Blower Door run?  Insulation?  Has someone done a Manual J?  How big is the basement?  Is it heated and cooled?  What about the insulation there? Where is the 2nd unit location?  Duct location.  Putting all this in the attic. Bad idea!

Why is the building owner adding on?  Why a 2nd story?  No room? Does he have a budget?  What are his goals with the day care and the addition?  Does the day care use the basement, storm shelter? How many kids and what ages at the daycare?

Most HVAC guys have a hammer and every answer involves equipment.  I would at the very least get another opinion on this one.  

Mr Nicholas,

I have been hired on to build the 2nd floor so that the owner can meet the expansion of the biz.  There is a waiting list of 16-17 people right now (16 kids min).  Which will bring the total count of 5 adults and 26+ kids in the building at one time.  If the owner didn't own the building already and if the location was poor I'd suggest to buy a better building and skip the remodel and the expense.  But since the location is good and building is owned I'll remodel the upstairs to meet the needs of this growing biz.

Furnace/Air Handler- Initial inspection age undetermined but looks fairly new 5-7yrs old guesstimate.  What I noticed (and was confirmed by the HVAC inspection) was that the metal ducts were not sized correctly and the soft ducts had kinks and other issues that inhibited the air flow.  It was no wonder the building owner had 3 window units to assist in the cooling.  The exterior compressor looks old enough to vote-so its past its prime / needs recharged yearly.

Basement: No Insulation, used as storage, laundry area, storm shelter. I would love to assist in making the whole house energy efficient and will discuss this while the owner and I are going over this with the Banker and the EEM mortgage.  My focus is mainly on the Second Floor Remodel right now so that the owner can grow the biz. 

The Second floor was designed/built for the original family to expand as the family grew and more room was needed.  It was never utilized as this and has remained as an Attic for 80+ years.  There is plenty of room to meet the planned growth of the day care with a little room leftover.  So we're not really building in an attic.  My design will have a very small attic above the ceiling with R49 or greater blow-in insulation.  I will also be adding Peak and Soffit vents, Insulation, Air Baffles- for natural air flow.

I do not plan to locate the 2nd Floor furnace in the Attic and will build a closet for this (not included with this drawing)  I would like to locate it where the sink is and move the sink towards the bathroom door.  The HVAC ducts I am planning to put in the Attic (I don't like this but I don't really think a soffit to hide these would look good-second option would be the loft type ducts that are exposed {while they look good in high ceilings I don't think the aesthetics will fit in this design}).  I will also insulate these ducts with a couple of layers of foam.

Thank you for taking the time to offer your suggestions.


Scotty, Have you considered closed cell spray foam?  Should speed things up and lower risk of QC and design failures:

While I like spray foam in this case because the Day Care will  never be closed I do not feel the benefit outweighs the possible health hazards.  Since the costs of spray foam vs conventional insulation is higher-I'd rather buy cool flooring materials instead.  The walls I build are on the inside of the Brick Home.  I'll have  total R19+ via equest building simulation.  R49 Attic Insulation, and R13 in the flooring as a sound barrier and energy efficiency.

Thank You for your thoughts.


Have you measured the building's leakage?

Will a blower door be used for any part of design, work, or quality control? 

I'll no more about how much money is available for the project after the meeting with the financier this coming week.  I'd sure like to have the testing done but if there is only so much money available my hands could be tied.  Whatever I do on the 2nd floor will be designed and built with more "energy efficient" measures than were utilized compared to the downstairs.

Thanks for all the feedback.


If you are looking at any kind of an EEM for residential property, you will need a HERS Rater.

If the existing flex is not well installed, replace.  If outside the envelope, buy R-8 insulation. If on the ceiling plane, bury the ducts in your blown material.

You need to get someone with eyes on the existing building to do your Manual J and D. Until you have those numbers any discussion of 1 unit or 2 is really not useful to push for energy efficiency.  BTW:  IRC in the Mechanical Chapters has required a Manual J and D for 10 years now. Same sections in IBC.  So anyone not being able to do this is not following code.

A Daycare with 26 capacity.  What are the state and local regulations for the physical plant!  Someone better be looking at those in the design stage.  You may have some plan reviews to get through or some specific variations on otherwise routine installation of items that will make everyone miserable unless you allow for it in the design stage.  I know that adult day care etc has many really specific regs that get enforced by Registered Nurses - not building inspectors.  

You may have more issues with these regs and reviews than what you have been talking about. Don't take the owner's word. Find out for yourself.  It is your license on the line (and your liability insurance.) Y

This sounds like a design build type remodel. You know it is for commercial day care, so you are on the hook to know the details.  That also makes it a commercial code issue and depending on the AJH it could be a zoning issue as well.

Ask the questions now!

Good Points.

Before any building will be done I will submit my design to the city for a Review of the Building Plans.  There are Issues the "Old Pro HVAC" has already pointed out and figured into the project on his end.  One of which is how we are going to get Fresh Air into the space per HVAC guidelines.  There is a few additional areas I'd like to address (if the budget allows) but my plans call for at a minimum of the way I would build it and not cut corners.

Thank you for your thoughts and suggestions.



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