Is an added vent needed?

pawn657July 30, 2012

We had an a/c unit installed last year as the existing one was far too small for the home. As this was done at the end of the summer we really did not have much time to see how it would perform during the peak Florida summer. We have this year and have an issue. Unfortunately company, one man, who installed it passed away and we are now left with the prospect of "advice" from all areas. The following is my question

We have the return in the ceiling in the hallway outside our bedrooms. The thermostat sits almost directly underneath it. There is no vent in the hallway. We have noticed that the thermostat will show 77 degrees and we have the a/c set on 75. We have had the t-stat replaced and had an insulation inspection, both are sufficient. It just does not cool down until sun goes down. Which means we either have to set air at 77 to avoid undo condensation on ducts or let unit run nonstop.

My question is, should we add a vent in the hallway to help the t-stat get a more accurate reading of the house? If so how far should it be from the return? House is only 1400 sq. feet and hallway is about 10-12' long.

Any help would be great as we are being hit with alternating opinions from every where. Thanks you in advance

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My home. like many if not most Colonial Style homes has both the thermostat and the upstairs return located in the upstairs hallway. My thermostat is directly below the return.

No problem.

I would think you would not want the thermostat directly in the path of conditioned air out of a supply. Also, I think the upstairs hallway is a pretty good representation of some kind of average temp.

It sounds as if your A/C is simply not up to meeting the amount of cooling to keep the second floor comfortable... this is not uncommon, particularly on older homes in my area. (MD)

    Bookmark   July 30, 2012 at 9:21PM
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We do not have an upstairs, only one floor. The a/c unit we installed is one step higher then specs call for just in case. We receive a rebate from our local power company and the tax incentive allowed us to go a little higher then we needed. Do not believe it is the unit.

If we did install a vent it would be about 8' from the t-stat and the return. Basically just to supply some air to the hallway. We had two a/c companies come in and this was one of their suggestions, other was replacing all of the ducts. Not sure why as the rest of the house is definitely cool enough. Our electric company checked each vent and they are blowing below standard temperature. Had this done for insulation rebate.

Trying to find a solution any help is appreciated.

    Bookmark   July 31, 2012 at 7:13AM
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I've never seen supply vent in hallway

in your 1400 sq ft one story home in florida
what size unit was installed?
what was the size of the one that was
'far too small' that was replaced.
are you aware that bigger is not better?

did the company who upsized the unit
tell you that your ducts would be too small
for the larger unit you had installed?
this is probably why another hvac company
mentioned changing ductwork.

by 'one step higher than specs called for' do
you mean that you put 14 SEER instead of
industry minimum of 13 SEER?

where are your ducts located that they
condensate? vented attic? crawlspace?

or is there some other meaning to this statement?

you could try a stand alone dehumidifier
to remove humidity. larger unit may have
short cycles that prevent it from running long
enough to dehumidify.

long run times are not a bad thing in a hot humid
utility companies don't troubleshoot for hvac.
they may shoot a couple of temps but they
don't know hvac.

best of luck.

    Bookmark   July 31, 2012 at 9:42PM
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"Our electric company checked each vent and they are blowing below standard temperature."

It sounds like you have an installation problem. You should have at least a 20 degree temperautre drop. Adding a vent to the hallway is not fix the problem.

    Bookmark   July 31, 2012 at 10:39PM
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The temperature is below the 20 degrees mentioned. One is at 30 others even lower.

The unit is a 15 seer and the duct work was reviewed at installation and nothing was needed. The ducts are the old metal ones and are located in our crawl space. That was the only thing mentioned that we should think of going to flex pipe some time in the future.

The old unit was one for a mobile home and was there when we bought the home. The people who owned home were trying to sell after father died and did a lot of fast replacements to get it off the market.

The only spot in the house too warm is the hallway with the t-stat in it, the rest of the house is way below set temperature due to it running to cool to t-stat temp. reading. That is why I one of the hvac companies stated it should install a supply in the hall. So, that is not a valid option?

    Bookmark   August 1, 2012 at 7:02AM
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It sounds like the hallway is two degrees warmer than the rest of the house because there is no supply vent. I think you want the house to be 75 degrees, but the AC is only able to bring the hallway down to 77. If you set the thermostat to 75 the AC runs all day with the hallway at 77 and the rest of the house at 75 or below.

Did I state the problem correctly? Do you mind the hallway being a few degrees warmer? Do you keep the doors of the rooms connected to the hallway open?

You could add a supply vent to the hallway, my conern would be stealing air from one of the other rooms. The simple solution is setting the thermostat higher in order to compensate for the temperature difference. This assumes you don't mind having a hallway warmer than the rest of the house.

    Bookmark   August 1, 2012 at 8:55AM
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so...what size was there originally
and what size was it replaced with??

this is a mobile home?

    Bookmark   August 1, 2012 at 1:08PM
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"It sounds like the hallway is two degrees warmer than the rest of the house because there is no supply vent."

I have owned many homes in many different parts of the country, most were two story colonials. Not one of those had a supply duct in the upstairs hall, most had the upstairs return in the hall, and all had the thermostat in that hall.

    Bookmark   August 1, 2012 at 4:46PM
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A 15-SEER unit should not have a +30F drop on the supply air!
IT MUST HAVE WAY BELOW THE REQUIRED CFM of AIRFLOW; also, there could be a very low humidity in the conditioned area.

You need to have the actual air flow CFM checked.

The indoor temp-drop from the supply outlets should be around 19F under normal CFM airflow & load conditions.

Under low humidity & the lowest airflow permitted 23F drops are about the usual limit for 15-SEER units.

    Bookmark   August 5, 2012 at 3:49PM
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This is what I am talking about. We have had two separate companies come to inspect and suggest and neither have mentioned what you are asking. The 30f drop is the first room it comes to and they said nothing about this being abnormal.

Thank you for your advice, I guess we will keep looking for a company that will give us the service and honesty we require.

    Bookmark   August 6, 2012 at 9:08AM
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If the stat is in the hallway the majority of rooms going into the hall have closed doors and or registers the air moving down the hall could very well be too warm because it isn't conditioned air. My parents have a ranch and with three bedrooms down the hall where the stat is located and if they only leave the master door open with the registers open in that room and the other two bedrooms with doors shut and registers shut the comfort level and stat settings go out the window and every room has a dedicated return.

With decent insulation and sealing and every vent blowing 25-30 degrees below room temp if the ducts were sized correctly and it ran all day you would need a coat. I don't know where but there is a serious problem and not only is it causing comfort issues I bet it is eating a hole in your wallet compared to being set up correctly.

    Bookmark   August 6, 2012 at 3:06PM
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I had a single wide 16x80 and the only difference between the system in it and a double was the line set was different. The single had a restriction in the high side fitting if I remember correctly so it was choked down. The hvac guy at that time cut it out because the O ring had a slight leak and he did away with the orifice and fitting and soldered a sleeve in its place. The unit was sized for a double wide after that and it blew over 30 degree cooler air which would wake you up if you stepped on a vent and was not near as comfortable in the spring and early summer because of the short run times and poor humidity control.

    Bookmark   August 6, 2012 at 3:26PM
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