Returns!!!!

[uk4545a]

I am in the midst of having (all Goodman products) a 3Ton Compressor, Coil, and 90,000 btu Furnace installed for my upstairs zone of my house. This was primarily driven because the old unit was a 2Ton and could not handle heating and cooling with the amount of venting that was in place.

here is my question, I am adding several more returns and one more vent to the system to keep the air moving well and increase the cooling/heating air flow. Is it better to have "the more the merrier" attitude as to how many returns you have? With the increase in returns at the furnace a vibration is occuring and he said he needs a larger (I forget the name of it, but it sounds like "Placenta") receiving unit for the returns.

Thanks for any insight.

[dcmcm5]

When you say "it could not handle heating and cooling with the amount of venting that was in place" exactly what do you mean?

You should do a load calculation to determine what size unit needs to be installed, rather than just guessing and hoping it will work. Get a contractor that will size the house and determine the correct unit for the load.

[uk4545a]

The HVAC compeny that I normally use said I have about 3 Tons worth of venting running on a 2 Ton unit. They gave me a quote to do everything and I went out and found someone to do it sunstantially cheaper.

The guy doing it now doeasn't seem to have an opinion one way or the other, he basically will do what I ask him to as it related to the venting and returns.

[pstu]

I am a homeowner and when I considered adding returns in 2004, the general advice from this board seemed to be that it is hard to have too much return capacity. I specifically tried to find out if there is a downside and believe there was none.

Just recently one of the pros here said adding return would add to static pressure. Sounds just the opposite of truth to me, however I figure this pro is so knowledgeable that he is addressing some subtlety that I don't know about. My returns were added primarily to reduce static pressure, we measured before and after, and it worked for that. A secondary reason was to increase airflow and that is harder to measure but I am certain it did. A third reason was to provide an air return path when bedroom doors were closed, a return in each bedroom guaranteed that.

Subsequently I have learned the best practice is to use ACCA Manual D to design both returns and supply ducts. It is my understanding that supplies are a lot harder to get right than returns, usually with problems of not enough airflow or poor distribution compared to heat/cool needs in particular rooms.

If you have "3 tons worth of venting" already then why the project to increase it? Sounds like a contradiction in your story, just wondering.

Regards -- Pstu

[uk4545a]

My master b-room is huge and had only two vents so I had another added. The Master bath is also very large with a cathedral ceiling and had 1 vent but no return so I added a return wbove the vent along just below the ceiling.
The final addition was a return in the upstairs hallway right in front of the two story foyer. The upstairs ahllway had only 1 vent and no returns so it is difficult to keep cool. With my old 2 ton unit it never got under 80 degrees if was over 85 degrees outside so the unit ran constantly. This is also where the thermostat is so I figured I need to keep more air circulting out there or the bedrooms will get very cold as the hallway tries to catch up.

What do you think about that theory?

[skippedover]

Airflow is a science. It's fluid dynamics and there are a whole host of additional considerations. For example, if you sleep with your bedroom door closed and the return is in the hallway, then the inrushing air from the HVAC system supply outlet will put the room under positive pressure. The end result of that is that air is force out of the room through every opening it can find, be it recessed lights, electrical outlets, ill fitting windows, etc. That means that when that air is forced out, fresh air has to be drawn in from outdoors somewhere else in the home. Sizing both the supply and return for EACH ROOM as well as for the whole house is the only way to go. If you're putting 150 CFM into the room, you should also be taking 150 CFM out of the room. If your system is 3-tons, the total airflow should be approximately 1200 CFM, divided appropriately between all of the conditioned rooms/spaces. There should also be at least 1200 CFM of return air available. Where some installations miss the boat is by not doing the engineering analysis on the actual grille on the return. Different grilles result in different airflows. When you have large, open spaces, they can serve as an opportunity to provide additional return air. We like to oversize the returns approximately 25% with variable speed products because of the increased airflow. With a variable speed product, if the duct system is undersized, the blower will ramp up to fulfill it's design CFM. If that means the velocity in the duct is going to 1,000 FPM, then that's what it will do. The result is a lot of noise and return grilles that will 'sing' lovely tunes to you. Probably not what you want. The ACCA has manual D to help with the duct design but the final touch is the diffusers/registers or grilles. If they're not properly selected, all the duct design is for naught. As I said, it's a science, not guess work. You get what you pay for. Do the job on the cheap and you'll pay dearly with discomfort. Pay up front with your checkbook and you should enjoy many years of comfort. The choice is yours.

[gonekuku]

90,000 BTU to heat your upstairs sounds excessive. Where is this home located, how old is it, how is your insulation, windows? How many Sq Ft is the upstairs?

How old was your old system? I hope you & your HVAC contractor are not assuming that since the old system wasn't heating & cooling well, you have to get a larger new system.

Perform load calcs.

[dcmcm5]

I guess I'll just have to claim stupidity, but what do you mean when you refer to "venting" since that could be interpreted in different ways? Are you talking about return air size?

[uk4545a]

By venting I mean outflow registers.

[uk4545a]

Oh, and the quote originally called for a 70,000btu furnace but he arrived with a 90,000 as he said it would be more efficient and he would absorb the additional 300.00 or so in costs. sounded peculiar but I didn't see any harm in it.

I questioned him about the efficiency and he said it wiould be better than the 70,000.

[Shophound]

By venting I mean outflow registers.

More commonly referred to as supply registers.


The HVAC compeny that I normally use said I have about 3 Tons worth of venting running on a 2 Ton unit. They gave me a quote to do everything and I went out and found someone to do it sunstantially cheaper.


I'm with the others...without a heat load calculation, without a room by room CFM calculation, without proper duct sizing, without a competent contractor who may charge you a little more...

YOU'RE JUST GUESSING!

Why guess with the largest consumer of electricity in your home? And the one system that has the greatest burden of making your home comfortable? And a system that ranks toward the top in expense should it need extensive repairs?

[tpa-fl]

My master b-room is huge and had only two vents so I had another added. The Master bath is also very large with a cathedral ceiling and had 1 vent but no return so I added a return wbove the vent along just below the ceiling.

Proper airflow has NOTHING to do with the NUMBER of grilles, rather it has EVERYTHING to do with the SIZE of them and the ductwork feeding them. There are precise formulas and calculations are used to determine the proper sizes needed.


The HVAC compeny that I normally use said I have about 3 Tons worth of venting running on a 2 Ton unit. They gave me a quote to do everything and I went out and found someone to do it sunstantially cheaper.

The guy doing it now doeasn't seem to have an opinion one way or the other, he basically will do what I ask him to as it related to the venting and returns.

Sounds like you're getting what you paid for then -- someone who doesn't know jack about air conditioning. Do they have an HVAC license in your state/county? Did they pull a building permit? Do they have their EPA certification card? Do they have insurance? My guess is that the answer to all of these questions is "NO" and you're possibly putting yourself and your family in danger. Also, most insurance cos will NOT cover any major claim in the house if they discover that the furnace/HVAC equipment was installed by an unlicensed contractor/unpermitted install.

What really tips me off that the guy probably doesn't know what he's doing is that he lacks an opinion on this. I've yet to encounter a good AC contractor who doesn't have a strong opinion about the way things should be.


Oh, and the quote originally called for a 70,000btu furnace but he arrived with a 90,000 as he said it would be more efficient and he would absorb the additional 300.00 or so in costs. sounded peculiar but I didn't see any harm in it.

I questioned him about the efficiency and he said it wiould be better than the 70,000.

And you're STILL using this contractor?!? Don't walk, RUN AWAY from this guy!!! I'm willing to bet he didn't even do a true heat load calculation. In which case, how the hell does he know what is too large / too small for your house? I'll give you an answer -- he doesn't. 20,000 BTUs is a huge difference. There's no way that it's going to be more efficient to run a 90k than a 70k, even if the 90k was a 95% and the 70k was an 85% unit. RUN AWAY!!!!!


What do you think about that theory?

It stinks. Get a real contractor in there and you'll be glad you did. It'll be cheaper in the long-run with fewer repairs and cost less to run as properly-installed, properly-sized equipment (including ductwork) is far more efficient than anything just slapped in place. Short-cycling that large 90k furnace is just going to kill it.

[m kilgore]

I agree with all of the above posters. Just a side note, around here its against code to have a return in the bathroom. The other guy (if theres any guy now) that was higher priced would have more than likely had a opinion and not just did whatever you wanted him to do.

[davidr]

Find yourself a contractor that actually measures the airflow & BTU's on the systems they install.

Designs are great but in no way a verification that the design was achieved.

The only way to insure you are getting what you paid for is if they can provide the actual measurements of your system for you.

[tpa-fl]

Just a side note, around here its against code to have a return in the bathroom.

Oh, c'mon.. don't you want to spread the stink of one's "morning constitutional" around the entire house? What's wrong with you? :D