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About Fred Weldin
Expertise
I can't help you if your whatsis won't work, people (Especially if it's a refrigerator); I have no experience with appliances, and I haven't been involved with H&AC service and repair since March 08, 1996 (Thank the Lord); I reject appliance questions and H&AC "Service and Repair" questions (about 18 a week), so if you want to know why your whatsis isn't working like it used to, ask someone else. I delete answers that are unread after one week (about three a month). If you have questions about how big a unit you need, if one room's warmer than the others, if you want an opinion on bids received, etc. just ask. Do visit askweldin.com, there's a lot of good information on sizing, ductwork, efficiency, as well as some techniques accomplished DIY-ers can use to troubleshoot and improve their H&AC. Finally, I want to thank all of the kind, serious people whom I meet here; I enjoy working with you.

Experience
50+ years in the business. See askweldin.com

Education/Credentials
B of ME U of D 1965, numerous classes and seminars since.

You are here: Experts > Home/Garden > Home Appliances > Heating, Air Conditioning, Fridge, HVAC > Min. distance between supply and return?

Heating, Air Conditioning, Fridge, HVAC - Min. distance between supply and return?

Expert: Fred Weldin - 11/5/2009

Question
QUESTION: Hello there, sir. I'm hoping you can give me some assistance with a problem I'm having with a new home construction. We are at the pre-drywall stage and all of the supplies and returns have been run. I'm specifically interested in our bonus room over the garage. This room currently has two supplies and a return, all in the ceiling, however the return is only about 1 foot from one of the supplies, and looks as though it was stuck in as an afterthought. It would seem that air entering the one supply would immediately be sucked back out through the return. I've attached a sketch of the way the room currently looks, and next to it is a layout I think may work better. Would love to get your thoughts on this.
This room will be used as a TV/media room with a lot of heat being given off by electronics. It's a room we'll likely spend a lot of time in and it won't be enjoyable to be warm the entire time.
Thank you so much for your insight.
Doug
IMAGE: HVAC

ANSWER: Doug:

First: The room must be a separate zone with its own thermostat, and a zone damper system is probably the best way to go; it's a Manual J requirement.

Second: I suggest you use a single "Diffuser" at the outside wall (I assume there's a window); it could be a three way blow, or a one way blow, the important thing is to have it blowing into the room, not towards the outside wall (the "secondary air" going from the room back to the diffuser will "wash" the outside wall and entrain downdrafts in the winter).

You're at the stage where a trip to www.askweldin.com would be worthwhile: Make sure the flex is installed to Industry Standard; if there's fibrous glass duct, check it closely (Pull off a branch and take images inside); and be sure to look for high resistance fittings. Stop everything if you see problems; your negotiating position is substantially reduced if you OK the next draw!

Fred

PS: Your AC is too big; now's the time to get that straightened out.

PPS: "...heat given off by electronics..." is no big deal today; some contractors use it as a scare tactic to sell more tons.

---------- FOLLOW-UP ----------

QUESTION: Hi Fred,

Thanks so much for your response. I've been thinking about your suggestions to my situation, and I wanted to respond to it to clarify a few things on my end.

You recommend a separate zone system for this room with its own thermostat. However, unfortunately I don't have that option. We've selected a canned floorplan from a local builder, and the HVAC is designed ahead of time. The HVAC for the house consists of two units - one for downstairs and another for upstairs. The thermostat for the upstairs is in the hallway attached to this room.

I'm not able to change something as significant as adding in a separate zone for this room. About the only thing I can do is maximize the locations of the supplies and returns to ensure the air will properly cool the room while circulating through it. How would you lay out the ductwork if you were to design the room? I thought my sketch might be better than the current configuration, but I'm certainly not an expert.

To answer your question, yes there is a window on the outside wall, which is the wall at the opposite end of the room as the door.

Do you know of anything in a building code that stipulates the minimum distance between a supply and a return? As I stated previously, in its current config air entering one of the supplies will immediately be sucked back out via the return, not giving it a chance to circulate through and cool the room. Any room I've looked at always has supplies on the opposite end as the returns.

Thanks again for your response. Let me know what you think based on this new information.

Best Regards,

Doug

Answer
Doug:

Let's start with the thermostat in the hall: The stair to the first floor is also in the hall, right? Do you think heat from the first floor will warm the hall and fool the thermostat (DUH)? Move the stat into a second floor room of your choice.

No, you shouldn't have returns near supplies; put the supplies at the outside wall.

Fred

PS: Good luck, it sounds like you're in for a good time; do delay the draw until the ductwork is right.

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