AC and Heat Issues

Problems related to residential installations.

Moderator: juster

Post Reply
Posts: 2
Joined: Sat Dec 29, 2012 5:13 pm

AC and Heat Issues

Post by hledford » Sat Dec 29, 2012 5:49 pm

We have been having problems with our HVAC system ever since we had our house remodeled and a new HVAC system installed. The HVAC guy that we have now has not been able to really help us that much so before I called someone else from afar, I thought I see what info I can get from here.

Brief History
The house was originally built in 1965 and was somewhere in the area of 1800 heating/cooling square feet. In 1976 the
carport was converted to a living room which bumped the sq footage up (sorry I don't have exact numbers). In 2007 we
remodeled the house somewhat by taking out walls and adding on, and now the total square footage is 1946. Before the house
was remodeled in 07, the air handler and all duct work was under the house in a craw space and the system was gas, and
the system worked pretty good. The new unit that was installed during the remodel was installed in a closet and ran into
the attic and the air vents were run through the ceiling. This new unit is electric. The old vents in the house to the
original unit were covered up with flooring. The old unit is still under the house with the duct work running from it.

Layout of Vents in house (with rough room dimensions)

Den Area - 3 Vents, room size is around 20*14
Living room/kitchen - 4 vents, room size is around 16*12 ***(Walls were removed in remodel to make kitchen bigger, so now
it joins with the living room)
Utility Room - 1 vent, room size is 12*12
Dinning Room - 2 vents, room size is 14*12 ***(This room is a new add-on in 07)
Bathroom #1 - 1 vent, room size 8*8
Bathroom #2 - 1 vent, room size 10*10
Bedroom #1 - 1 vent room size 12*12 ***(a/c handler is in closet in this bedroom)
walk-in closet - 1 vent, room size 7*7
Bedroom #2 - 1 vent - room size 12*12
Bedroom #3 - 2 vents - room size 12*12 ***(this room is now a computer/work room, it has 2 to 3 computers running)
Short hallway connecting rooms

The hvac unit -
The air return/filter is in the hallway. The thermostat is also in the hallway.
This is the model numbers on the unit we have.

Rheem Classic Series
Outside unit is model number - RPNE-048JBZ
Inside unit is model number - RHLA-HM4821JA
White Rodgers thermostat.
20" * 20" air filter

This unit also has a issue that we can never get our hvac guy to pinpoint. When we were using the A/c, right before it
came on, it would make a clicking/ticking noise for about 5 mins or so.

The -

The Den, Living room/kitchen, Dinning Room, and connecting hallway are cold in the winter and do not feel like the system
is heating the rooms properly. We have to run a set of gas logs in the den to help heat that area of the house. The same
can be said about Bedroom 2 and 3. Bedroom 3 especially, it has the 2 vents in it to keep it cool in the summer because
of the computers running constantly, but that room still climbs up to 88 at times in the summer when the thermostat is set
to 73. The heat from the computers in the winter help keep it warm somewhat. Wouldn't a room with 2 vents be burning up
because of the heat or freezing because of the a/c? The vents in the other parts of the house do not feel like much air
is being pushed through them. The original system really pushed a lot of air out. Also the original duct work was
aluminum duct wrapped in fiberglass. The new duct work is aluminum nor is it heavy like the original.

From the information I have gathered and posted here, is the unit we have strong enough for this house?
Would maybe changing the duct work out with the heavier sheet metal type help air flow?
Do the multiple vents in a small room really have a BIG effect on temperature, like bedroom 3?
Do we need to move the thermostat down the hall towards the cooler end of the house??

Thanks for any help and information.

Most Valued Contributor
Posts: 1019
Joined: Sat Jun 18, 2011 11:26 am

- AC and Heat Issues

Post by Freon » Sun Dec 30, 2012 10:57 am

The first step is go to each room and feel the air flowing from each register with the room door open. The perfect design will have the force (velocity) of the air from each register equal. Many times colder rooms are not getting the correct amount of air flowing into them.

The next thing is look at where the return registers are. Returns are where the house air returns to the furnace to be heated again. Many poor designs have returns that are too small for the furnace thereby choking the overall air flow.

If the returns are in a central area, like a hall, then you need to ask, How does the air entering a room get back to the return. Some rooms are open all the time and there's no problem. Other rooms where the door may be closed can have problems since there is no way for the air entering the room to exit. One way to solve that is cutting 1" off the bottom of room doors so the air can flow under the door.

Another design problem involving the ducting is flex duct. It has a higher coefficient of friction thereby making the air flow less. Poor installations will also have 90 degree bends in the flex that literally chokes the air flow altogether. Fortunately there are ways to fix that.

You will need to draw a diagram of your new ducting. You need to know the diameter of the ducting. At the furnace supply plenum the ducting diameter should be the biggest. As the duct goes through the house to various rooms it will decrease in diameter. I will assume all the supply registers are connected to 6" ducting.

The next question is the BTU output of the new furnace compared to the old furnace. Did the installer do a load calculation. Were you comfortable on the coldest winter night with the old system.

To save money installers do hurried jobs and there can be problems. I think your problems can be fixed with a little work once you understand exactly what you have for a heating plant.

Posts: 2
Joined: Sat Dec 29, 2012 5:13 pm

- AC and Heat Issues

Post by hledford » Mon Dec 31, 2012 4:45 pm

First of all thanks for the response. When they put the new system in, I don't think they did a load calculation. I will try to have someone come in to do a load check on the heat as soon as possible.

From walking around the house and feeling the air being pushed through the registers, they are not all pushing the same amount of air, some are stronger than others in the same room.

We have one return in the house and it is dead center of the house in the hallway. It sits over where the old original system was that is under the house. The closet that the new system is in butts up against the return area. The bedroom with the 2 registers (smallest room in the house, my size was off) is directly across from the return in the hallway. The door to this room stays shut, but there is a 3" gap at the bottom due to floor hights. Also, back last year we cut a pocket door between that bedroom and bedroom 2. The other 2 bedrooms doors stay open and are no more than 6 feet from the return. There are no doors on the other side of the house (normally colder side), it is wide open so air funnels down the hallway.

The duct in the ceiling is flex. I have been up there a few times to check it to make sure insulation or anything else wasn't on it crushing it. There are 90's in it.

All registers are connected via 6" ducting. From what I can tell all the duct work in the house is 6". None of it is smaller or bigger than the rest. I can't tell how big the furnace plenum is, but will see if i can get a size.

The older gas unit that we had under the house (and still is) worked great, but when it was in use, the part of the house that was remodeled had walls between each room, and now it is one big open area.

Would having the two registers in one room like I mentioned earlier make a room hotter or colder depending on heat or air?

Again, thanks for the help and info. I am going to work on getting someone to come in and check our problems.

If I can I will try to draw out the house and where everything is and post it. Maybe that will help.

Most Valued Contributor
Posts: 1019
Joined: Sat Jun 18, 2011 11:26 am

- AC and Heat Issues

Post by Freon » Tue Jan 01, 2013 11:33 am

More registers per room equals more air flow to that room equals more heat transfer.

If all the ducting is 6" then it is possible the rooms farthest away from the furnace will have the least air flow. Usually you'll have a main, large, trunk line from the plenum feeding the smaller lines going to each room. Closer rooms may only need a - feed from the trunk while rooms further away will need a larger diameter feed. Smaller the diameter the more friction reststance and the less air flow as the length of the duct increases.

If you have someone come make sure they check the return size. Many times the returns are inadequate for all the supply lines to the rooms.

Post Reply