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Placement of supply vents

geode's picture

We are building a home with SIP walls(R-26) and conventional trusses (R-50 cellulose). Most of our windows are south-facing (Low e, fiberglass), shaded by deciduous trees in summer. We are getting a geothermal heat pump, radiant heat in the basement, first floor, and 2nd floor bathrooms. We're getting some ductwork, mainly for AC and HRV air supply. Our feeling is that we will very rarely need to get heat to the upstairs with forced air. In our current, leaky, 1928 house, we have all the vents upstairs closed off because it gets so much hotter than the downstairs. Based on our experience here, we would like to have the supply vents for our new house located high in the wall on the 1st & 2nd floor (or in the ceiling), because our main concern is with getting the upstairs cool during the summer. Are we being foolish? Since our current house is forced air, it is hard to know if we will get the same heating effect upstairs with radiant.


We're in lower Michigan.

(post #112505, reply #1 of 15)

I'm just to your south, outside Toledo.

We have a partial open floor plan, passive solar using South and SW glass.  HW in concrete 1st floor, HW under ply/ceramic in the upstairs baths.  Two 4' HW basebd sections in to remote BR's and nothing but a big opening to the downstairs in the masterBR.  Cooled in spring and fall with a whole house fan.  Cooled in the summer with a window ac in the master BR.

I was concerned with heat rising like you are.  With our one side open to the 2nd fl ceiling and open downstairs floor plan I was surprised when the upstairs didn't get overly hot.  Heat rises but our ceiling fan seems to move it around enough and remember, radiant is just that.  The floor is warm.  There's some heat going up, but not the volume that you get with forced air.

Same thing goes with the window ac.  Expected the cool air to go out that big opening overlooking the LR, but it doesn't fly downstairs.  Gradual cooling throughout the whole house with a "you could hang meat" temp in the BR.  We keep it on energy saver and usually turn it down at night so it cycles on and off.

The key is the orientation with good sized overhang, the trees you have in the right location to block the hot aftn sun.

We did build it partial in the ground at the north/northeast side, live on a hill so the wind gets directed up and over the house and got some good insulation by '87 standards.

I hope I have helped a bit.  Where are you located in Mi.?

A great place for Information, Comraderie, and a sucker punch.

Remodeling Contractor just outside the Glass City.

Quittin' Time


A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


(post #112505, reply #2 of 15)

We're near Ann Arbor. I come to Toledo all the time with my kids (great zoo and COSI of course).

We would like to just add some radiant upstairs and skip ductwork altogether. We're not really sure we'll need ac, but it would be way more difficult to add ductwork later, than to just plan on it now. Because it's a geothermal unit, we don't have to pay more to get AC--except for the ductwork of course.

Thanks for your reply, it's good to have input from someone with radiant heat.


(post #112505, reply #4 of 15)

When you plan your bath, and if you have a deck tub, run some hose up under that deck ledge and maybe even around the tub base.  Makes for no shock to the fanny on tile and a longer warm bath.

Also, no hose runs under the vanity/kitchen cabs, no need for heat there. 

A great place for Information, Comraderie, and a sucker punch.

Remodeling Contractor just outside the Glass City.

Quittin' Time


A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


(post #112505, reply #3 of 15)

I don't see how you can make any energy/HVAC comparisons between your old house and the new one you are building.  Apples and oranges.


(post #112505, reply #6 of 15)

Hence the reason I'm asking! I don't know anyone who has radiant heat, much less anyone with a house as insulated as ours is going to be. Of course, convincing my DH that we might not get the same overheating upstairs that we do now is infinitely more difficult.


(post #112505, reply #7 of 15)

I'll step in here again if I may.

"Since our current house is forced air, it is hard to know if we will get the same heating effect upstairs with radiant."

Why not add light-weight, dry, low mass heat to the floors in the second floor and put that in it's own zone.  Easy and cheap to do now...very difficult and expensive to do later.  Even if it turns out you never turn it on, you've got that option for now and at re-sale time.  Maybe the next occupants want to sleep really warm.

This is assuming that the other floors will be slab/gypcrete.  What the heck, if you are now considering gypcrete in the first floor, why not go light-weight there as well?

(post #112505, reply #8 of 15)

What do you mean by light-weight? A staple-up system?

The first floor won't be gypcrete--out of our budget (which was stretched pretty thin to accomodate radiant at all). We'll be doing 2x4 sleepers with sand--which I know not everyone agrees with, but we thought it would be better than a staple up.

We are considering staple-up for the 2nd floor....but now it's a matter of how much time we have to get all the tubing in before the HVAC sub comes out (on top of all the other things we are doing), and then we'd need to insulate below, which seems like it would be very time consuming...too many decisions!

(post #112505, reply #9 of 15)

I'm with you on too many things to do and schedule...from your first post it sounded like you were subbing alot out.

How much is your HVAC guy doing?

Anyway, "light weight" as applied to radiant floors is anything NOT using cement or gypcrete.  The relatively new existence of technology...both the materials (aluminum plates with various well-tested methods of installation and control systems)....has made it increasingly possible to create systems with PEX tubing, aluminum and some sort of wooden sleeper system.  There are lots of very good ready made light weight systems available, like Quik Track, Warmboard, Rehau, to mention a few, and aluminum plates of all sizes and thicknesses (Thermo-fin gets good reviews).

Not to be-little your use of sand and sleepers, just that all of my research on both DIY and "patented" systems hardly brings up any sucessful examples using that method, while there are legions of sucess stories surrounding light weight systems in general (mine included) and all kinds of data to support the sucess.

But I'll repeat that if you really have serious doubts about heating the second floor, it's alot cheaper and less time consuming to deal with it now than a long shot.


(post #112505, reply #12 of 15)

In terms of HVAC, we're laying the PEX. We're trying to take over the time-consuming manual tasks that would be costly to pay someone else to do, but don't take a whole lot of skill. The HVAC sub will connect the pex up the heat pump, and put the ductwork in.

We've gotten ourselves into quite a bit of trouble with the "it's easier to do it now" mindset. I still can't fathom how much this house is ending up costing us for being a relatively modest 2200 sq ft. We're trying to use high-quality materials where it counts--but it doesn't leave a lot left for things like cabinets (IKEA, here we come!).

Thanks for your insights,

(post #112505, reply #14 of 15)

Jo, take a deep breath and plan the rest of this place b/4 you go any further.  Seems like you are in a rush to do the planning that should have been done b/4 you broke ground.  Any rushed decision now might be regretted later.

Remember what I said re. the heat on the second floor.  With radiant in our place, the open floor plan and path to the upstairs has not flooded the 2nd floor with heat.  What does the hvac guy suggest.  This can't be his first radiant house.


A great place for Information, Comraderie, and a sucker punch.

Remodeling Contractor just outside the Glass City.

Quittin' Time


A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


(post #112505, reply #15 of 15)

google "home energy magazine" if this is a real magazine I'll eat my shirt, but you can learn more about energy in a home here here than anywhere i've found

(post #112505, reply #5 of 15)

I think you've got it right on.

From my readings, and from having built a house similar to yours, one of the advantages of radiant heat is that you can optimize the delivery systems for both heating and cooling seasons, and you are wise to put in ducting as you plan.

I wish I had been as fore-sightful and added ducting in the planning and rough in stages.  As it is, I'll need to retro-fit ducting for an HRV system.  Not really hairy but no fun either.

Here's an example of how different radiant floor heat is than forced air heat or even radiators:

My recliner, a big over-stuffed beast, sits over several runs of PEX and plates, and even now, early in the heating season, it's almost uncanny how warm that chair is...but when you think about it, since I'm running a low temperature, nearly constant circulation system, the steady low temp radiation is warming the chair from the inside out.  Same effect with cold sheets in the bed.  During the half-dozen or so days that we actually have the bedroom floor "on", the sheets actually warm to a slight degree.

Edited 10/28/2005 8:53 am ET by johnnyd

(post #112505, reply #10 of 15)

Something that I did with my home that you may consider: between floor use wood trusses, not TJI's, and put all of the ducting between the floors.

Running a supply up the wall of every room on the second floor will get costly. Wall stacks/head/register combinations are not very effective supplies, even though the relative location is better than the floor. It is well documented that air distribution from the ceiling in cooling applications is the most effective manner of delivery, however, if properly selected for the correct throw, floor supply registers will work just fine. This would be recommended over any ducts in the attic.

(post #112505, reply #11 of 15)


Too late for trusses--although I tried hard to convince DH that we should get them for ease of installing mechanicals. Oh well.

So you're saying that we're better off having floor registers for the AC than to put them in the ceiling? Even buried under 2' of insulation? Do you have any online resources you could direct me to--my husband is a scientist and likes to look at data.


(post #112505, reply #13 of 15)

Since running ducts between floors is impractical, I would not say that floor supplies are better than ceiling supplies. IF, you have the opportunity to keep the ducts completely within the conditioned envelope, that would be prefered to running them through the unconditioned attic, no matter how well seal and insulated.

The greatest single source of information and data on HVAC is the American Society of Heating, Refrigeration and Airconditioning Engineers or ASHRAE. They have a website and a monthly journal as well as annually published Handbooks. The 2001 Fundamentals or the 2005 Fundamentals Handbooks would provide you and your DH with more information than most folks ever see on this subject. Air distribution and duct design is but a small segment of this publication.

Ceiling supplies will work very well. Seal and insulate the duct well. Check the air flow and the "throw" of the diffusers/registers selected, and wherever possible try to locate returns oppsoite from supplies (i.e. supply in the ceiling at the south end of a room, put the return near the floor on the north end of the room). The throw for vertical mounted registers should approximate the room ceiling height, for horizontally mounted registers 1/3 to 1/2 the width or length of the room.