Faster blower for furnace/AC?

[trader4]

A friend has a house with two gas furnaces and AC. The downstairs one is OK, the upstairs which is based in the attic is very marginal at best. The biggest problem is that there is not enough air flow. It's really only a problem in AC season, when it takes a very long time to cool. It has to run most of the day just to keep it at

2. It would appear that is due to a number of factors. The way they did the ducting is far from optimal. Right off the furnace the duct makes two 90deg turns, then feeds down a long duct off of which come flex hoses that feed 5 bedrooms and two baths. The furnace is located close to one long side of the house. Three of those supply hoses have to go up close to the peak of the roof, going across to the other side of the house. They did that to avoid going straight across the attic floor, leaving space for walk-in accessibility, which is good, but it comes at a cost. The return ducting is good. The AC itself appears to be working, the air coming out is 15 deg cooler than going in, closer to 20 deg right at the unit.

So, looking at this, I can see some possible improvements. Obviously doing something with the ducting would be beneficial. But I also looked at the blower and right now it's a 1050 RPM 1/3 hp. I'm thinking part of the solution could be to go to a 1650 RPM, 1/2 hp, which should be a drop in replacement. I know it's not a total solution, but even if the ducting stuff is straigtened out, given the length of the runs, etc, I think having the more powerful blower would still be part of the solution. Being that the blower motor is easy and cheap to do, I wonder if it makes sense to just try it and see how much it helps?

[hrhofmann]

What diameter are the supply hoses, and I hope they are insulated???!!!

[recyclebinned]

Just one question: When you or your friend says that =93the upstairs which = is based in the attic is very marginal at best=94 do you have the downstair= s on? What I mean is: Are you considering the house as a whole before you m= ake your judgment? In other words: If you don=92t have both the downstairs = AND the upstairs air conditioner on at the same time the hot air is simply = going to rise and make the upstairs hot.=20

[trader4]

Hide quoted text -

Yes, they are insulated as is the rectangular duct itself. I didn't measure the duct, but I'd say it's about 20 x 10? The furnace is horizontal. The crazy thing, IMO, is that they could have come straight off the top of the furnace, ie in the direction the air is already moving. Instead they did two

90 deg turns before starting the long straight run across the attic. Near the end, it gets reduced down to another duct about half the size.

I should also point out with regard to upping the blower that right now it's two speed. So the 1050 rpm speed is for cooling, heating is the lower speed, maybe 750? I found an equivalent motor that is

3 speed, 1650. So, could use 1650 for the AC, the lowest speed, which is probably 1300 or so for the heat. Could also use 1300 or 1450, etc for cooling if the 1650 doesn't work out for some reason, eg noise?

Jus thinking if this quick, easy and cheap solution makes a big improvement, maybe could avoid screwing around with the ducting? Another thing that sucks, IMO is that they put the furnace near one end of the area it serves. They could have positioned it another 10 ft or so towards the center of the area it serves.

[trader4]

h is based in the attic is very marginal at best=94 do you have the downsta= irs on? What I mean is: Are you considering the house as a whole before you= make your judgment? In other words: If you don=92t have both the downstair= s AND the upstairs air conditioner on at the same time the hot air is simpl= y going to rise and make the upstairs hot.- Hide quoted text -

The downstairs is at like 77F, which is a comfortable temp. But you have a point. If the downstairs was set to 72, it would probably make the upstairs a lot more manageable. I forget the exact split, but as I recall the total AC is like 5.5 tons, no more than 6 for sure, with it split 60/40, the 60 being the downstains. The house is 4100 sq ft. Another thing that sounds kind of dumb, no? I'd put more of the AC capacity up top.

The sad thing is the house is like 7 years old and this isn't rocket science. You would think by now they would be able to do this right.

[Ed Pawlowski]

It may help, but it may not. Sure, it will move more air, but if the unit does not have the capacity to removed the heat from it, the faster blower just moves warm air faster.

Have you checked the temperature drop over the coil? That will tell a lot.

[Stormin Mormon]

The often neglected aspect of low air flow, is return air ducts. Often under sized.

With 5.5 tons for 4000 sq feet, seems like it ought to cool. Please have a HVAC pro come out. He should clean the outdoor units with foaming chemicals, run till they dry and then check the freon. And a few other checks. If your system needs maint, you may have 5.5 tons of equipment, but not be getting that much cooling.

I worked on a house, couple years ago. The guy was stuck on "if it's got 3.5 tons and not cooling, we need 5 tons or six". Several lack of maint problems were there, and he was getting nearly no cooling. I repaired the system, and life improved a lot. SWMBO was pleased, too.

Christopher A. Young Learn more about Jesus

.

manageable. I forget the exact split, but as I recall the total AC is like 5.5 tons, no more than 6 for sure, with it split 60/40, the 60 being the downstains. The house is 4100 sq ft. Another thing that sounds kind of dumb, no? I'd put more of the AC capacity up top.

[trader4]

All that is good, but if there is very limited air coming out of most of the registers, not just very little cold air, but very little air period, then I don't see how anything maintenance related is going to do squat. It has an electrostatic type filter and it's clean.

[Ed Pawlowski]

But, as Chris points out, if the inlet is restricted, the outlet won't have an air to move. Do check that part if you have not already.

[recyclebinned]

I have had to work on air conditioners where the previous residents had ope= rated them without an air filter causing the evaporators to become clogged = with dirt. I know the answer to this but I=92m going to ask it anyway. Do y= ou have an access panel or door on your evaporator coil that you can check = from? Air conditioner installers never put one on residential units but alw= ays put one on commercial ones for some unknown reason. You will need to in= stall an access panel or door and you need to do it without cutting the sof= t copper refrigerant lines while doing it.

[hrhofmann]

But what size are the supply hoses, I asked about that before?? Is the problem low flow of very cold air, insufficient coldness of lots of air, or something in between???

[Rick]

Unfortunately the horsepower required to turn the same blower at the faster speed varies as the cube of the speed ratio. Depending on where the system restriction curve falls on the blower performance curves, 1/2 HP probably ain't gonna get it.

[David Whitfield]

Check the RA vs supply dimensions. Works much better if RA can hancle about 10% more volume than supply. I had a similar problem a few years back with geothermal units. Downstairs unit for 2,800 sq. ft. was great. Upstairs unit (1,800 sq. ft.) had problems similar to what you describe. It turned out that the upper unit had insufficient return-air. Additional RA vents added, problem solved. That was 16 years ago.

[Stormin Mormon]

Oft neglected, because people don't see how under sized returns could "possibly" affect the air out put.

Christopher A. Young Learn more about Jesus

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But, as Chris points out, if the inlet is restricted, the outlet won't have an air to move. Do check that part if you have not already.

[Stormin Mormon]

That's true, a dusty and dirty evaporator would reduce the air flow. And, you're right not to cut the copper tubing.

Christopher A. Young Learn more about Jesus

.

I have had to work on air conditioners where the previous residents had operated them without an air filter causing the evaporators to become clogged with dirt. I know the answer to this but I?m going to ask it anyway. Do you have an access panel or door on your evaporator coil that you can check from? Air conditioner installers never put one on residential units but always put one on commercial ones for some unknown reason. You will need to install an access panel or door and you need to do it without cutting the soft copper refrigerant lines while doing it.

[trader4]

That's interesting. I figured it would go up, but wasn't counting on that much! Fortunately the sub motor is 3 speed and the lower speed is probably

1300 rpm or so. Maybe that will be OK at 1/2hp

[bud--]

Is it actually running at 1/3 HP now? (Amp clamp and compare rated current.) (Current versus hp is not particularly linear; watts vs hp probably is.)

Don't remember it coming up (and way too obvious) - air filter is not clogged? Dampers not closed? (particularly to farthest run).

[Vic Smith]

Air flow in vents is hard to figure. I've got one room closer to the furnace than others, same size vents, but it's always cooler in the wintertime. If the A/C is putting out the BTU's for the entire house, but the air can't get upstairs, I'd look into booster fans. They sell vent boosters and in-line boosters. Might be the more cost efficient way.