HVAC question #2

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LoneAspen

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LoneAspen
Seeing the other HVAC question somebody posted made me realize we probably have some HVAC experts here, and I could ask this here...

The house I bought is a two story located in Colorado, about 3000 square feet, equally divided between the levels (both levels are fully finished). I think the style would be called a raised ranch, as the bottom level is half buried in a hillside.

It has two completely separate natural gas furnaces. There are no A/C units, just heating. The two furnaces don't cover each level of the house, they cover each side of the house.

The problem I'm having is that the upper level will sometimes get too warm, while the lower level is too cool. If I turn one, or both, of the furnaces up to get some heat into the lower level, it's also putting out heat in the upper level, making it even warmer.

Why somebody would plumb furnaces to cover each SIDE of the house instead of each LEVEL, so each level could be heated individually, is beyond me. Seems a strange thing to do.

I'm wonder how involved and expensive it might be to have the system redone so the furnaces cover each level of the house instead of each side? Has anybody ever had something like this done?
 
Start simple, don't redo the system. You said furnace, so I'm assuming forced hot air. I think you just need to balance the systems. You have too much heated air going to the hot areas, and not enough going to the cold areas. I'm also going to assume that the cold areas do not have obvious issues like leaky windows or big drafts.

The duct work or registers of these systems usually have dampers installed that can be adjusted. You want to adjust those dampers. The goal is to get more heat to the cool areas and less heat to the warmer areas. Make sure all filters are clean. Then find the dampers. If the cold area dampers are closed partially, open them up some. Wait a day or so and see what happens. If the warm area dampers are wide open, close them down a little. Make small adjustments then wait at least a few hours and see what happens. Also, don't go by feel for the temps, use a thermometer in each area, just leave them there and compare numbers. After a few days you should be able to get it balanced out. Remember, the goal is to not restrict the system too much when closing the dampers. Some should be wide open, (probably the ones in the cool areas) others should be only restricted enough to balance the temps through out the house.
 
Yeah, I go through this exercise twice a year. Once to balance the A/C to throw more cold air upstairs and again to balance the furnace to throw more warm air downstairs. I mark the dampers in the basement "summer" and "winter" so I can remember how to adjust them.
 
Are the two furnaces in the same room? Are there air returns from each level? If the answer to both questions is yes then maybe the levels can be split with some duct work at the furnaces. If even one of the answers is no then a bit of work will be required to even answer the ‘can it be done?’ question.
 
Thanks for the replies so far!

By dampers - do you mean the registers in each room? Excuse my ignorance, but I'm not that familiar with HVAC systems except for twisting a thermostat dial.

The furnaces unfortunately are in separate rooms, and I'm pretty sure there's an interior concrete wall separating them. I'll have to check on where the air returns are. I know the furnace for the right-hand side of the house has a return on the lower level, and I'm pretty sure it has one in the bedroom upstairs also. I believe the furnace for the left-hand side of the house has a return on the upper level (in a short hallway), and might also have one in the stairwell.

Sounds like the furnaces being in separate rooms would be problematic. The right-hand side furnace is in a pretty large storage room. The left-hand side one is in a very cramped utility room where the gas water heater is also located.
 
LoneAspen said:
Thanks for the replies so far!

By dampers - do you mean the registers in each room? Excuse my ignorance, but I'm not that familiar with HVAC systems except for twisting a thermostat dial.

The furnaces unfortunately are in separate rooms, and I'm pretty sure there's an interior concrete wall separating them. I'll have to check on where the air returns are. I know the furnace for the right-hand side of the house has a return on the lower level, and I'm pretty sure it has one in the bedroom upstairs also. I believe the furnace for the left-hand side of the house has a return on the upper level (in a short hallway), and might also have one in the stairwell.

Sounds like the furnaces being in separate rooms would be problematic. The right-hand side furnace is in a pretty large storage room. The left-hand side one is in a very cramped utility room where the gas water heater is also located.
Click to expand...

The dampers could be on the register, where the air comes out or near the furnace, there might be a lever on the ducts that go to the register. Think of the damper as a valve on a water faucet, open it up more air flows, close it down, less air flows. A few pictures might help us figure things out. It really sounds like a balance problem to me.
 
Our split-level house has HVAC for one side of the house and the other, versus upstairs/downstairs. We just adjust the floor registers as needed to balance out the needs of each room.
 
Regardless of your system(s) one thing I strongly recommend getting thermostat(s) that have a “circulate” function.

This will help to balance out the air temps even when the unit(s) are not running to heat / cool. It’s a fairly inexpensive way to substantially improve the efficiency of your home. I have installed them in my home and business and I have basically eliminated the “yo-yo” adjusting that my wife and employees were always doing.

The ones I have will circulate air (fan mode) about 10-15 minutes every half hour.
 
LoneAspen said:
By dampers - do you mean the registers in each room?
Click to expand...

In my HVAC system, I have a single large duct that goes to the 2nd floor, and two more that go out to each half of the first floor. Inside those lines are dampers that can be opened, closed, or put somewhere in-between. Full open puts air evenly to all ducts. Warm air rises and the thermostat is normally downstairs. So your furnace heat rises up the stairs and your 2nd floor gets hot because your furnace is already putting air up there anyway. Eventually the first floor warms up enough for the t-stat to turn the furnace off but by then the upstairs is too hot. Adjusting the dampers to put more warm air downstairs and letting that air drift upstairs to warm it that way allows for a little more even heating.

Look near your furnace for something that looks like this:

msl_heating_systems3.jpg


B473198.jpg


When the lever is in-line with the duct, it's full open and when it's at 90-deg it's closed.

Another trick is to take some needle-nose pliers to those cheap registers and bend the diffuser vanes to guide airflow into the room instead of along a wall or into a corner or under a couch, or behind the curtains, or whatever.
 
arkvet said:
Regardless of your system(s) one thing I strongly recommend getting thermostat(s) that have a “circulate” function.

This will help to balance out the air temps even when the unit(s) are not running to heat / cool. It’s a fairly inexpensive way to substantially improve the efficiency of your home. I have installed them in my home and business and I have basically eliminated the “yo-yo” adjusting that my wife and employees were always doing.

The ones I have will circulate air (fan mode) about 10-15 minutes every half hour.
Click to expand...

Most thermostats have a switch labeled "fan" with two options, Auto and On. When the switch is in auto your blower only runs when the furnace/AC does, if you set it to On the blower will run continuously which should help your problem somewhat. It also may help the longevity of the motor itself as the lions share of wear and tear occurs on startup and shutdown.

My house is a split level and temps would tend to stratify on each level with the upstairs being much warmer than other areas, simply running the blower all the time made a considerable difference.
 
We recently had to make a choice for our ex-pole barn, now home with garage. It was just a bit more, but we opted for two separate units, one for upstairs and one for downstairs. The idea being only one area might be in use, and the one below grade will likely be cooler in the summer anyway and need less cooling. We could have done it with ducting, but like the redundancy of a second unit.
 
"Crankshaft" strikes again huh? Sorry, not a lot of help here, because it's extremely difficult to diagnose, then offer a long distance solution without an actual walk thru, or a set of architectural and mechanicals. Besides, I hate residential with a passion.

Anyhow, you'd need to know the physical layout of the envelopes, the calculated loads, the units, design airflows, duct layout, return locations, etc., etc.. Trying to adjust airflows at the grill face is not acceptable in a properly designed and installed system. Utilizing two units is a common energy saving practice, if done properly. It's hard to say right now whether or not you have a properly designed system that can be balanced, or you need some modifications? You need to find a local who knows his business. You might start out by telling the tech you think you might have an air distribution problem, then ask if hes ever heard of a thing called an airflow hood. (Shortridge, or Alnor) Good luck.
 
Kansas Flyer said:
Most thermostats have a switch labeled "fan" with two options, Auto and On. When the switch is in auto your blower only runs when the furnace/AC does, if you set it to On the blower will run continuously which should help your problem somewhat. It also may help the longevity of the motor itself as the lions share of wear and tear occurs on startup and shutdown.

My house is a split level and temps would tend to stratify on each level with the upstairs being much warmer than other areas, simply running the blower all the time made a considerable difference.
Click to expand...

I’m not an HVAC expert but have read and been told many times that running the fan all the time (leaving it on fan mode) is not a good practice. I believe it has something to do with not allowing the moisture to collect and drip off the coils when the fan has stopped.
 
Constantly running the fan in a forced air system, depending on the system, can be a good thing, however, it will increase your energy consumption, (your electric bill).

Without getting into long winded specifics, for a multitude of reasons, it can increase your indoor air quality and comfort.
By the way, constant fan, with acceptable airflow velocities across the cooling coil, helps to keep the coil dry, which is extra insurance against the biological growth that can occur in that part of the system.
Next time one of your experts tells you otherwise, ask them, "why does my indoor unit continue to run for a minute or two after the outdoor unit has shut down". Maybe it's a factory design flaw?
It'll probably be like trying to have a discussion with some of the other members of the national brain trust that can't make the connection between the ridiculous costs of general aviation and over-regulation.
 
Don't some of the really high efficiency systems have a multispeed fan? When the furnace or AC is running, the fan goes into a high speed mode, otherwise it shifts down to a low speed mode to quietly keep some airflow moving around the house.
 
In the past several years the residential market has been borrowing some of the technology that the commercial market has used for decades. Variable volume technology, zoning, etc., is nothing new. It can save on operating costs, but is more complicated, and expensive to purchase and maintain. To maintain, "Crankshaft" needs to be up to speed, or the building owner finances his education.
To answer a few questions some might have...sort of.... and this explanation is very simplified.

In a simple commercial variable volume 4 pipe system (chilled water, hot water), the air handler will supply minimum outside air, a constant discharge air temperature (normally around 55 degrees), and maintain a constant static pressure (normally around an inch or so water gauge) in the main supply duct. The pressure independent VAV (variable air volume) terminal units will maintain their (internally programmed) heating and cooling maximum and minimum cfm setpoints depending on zone setpoint and condition. The VAV will also contain the reheat capability for the system.

With the equipment and technology in use today, it's generally more difficult to remove btu's than it is to add btu's, hence, less cfm (lower airflow) is normally required to heat a zone, and more cfm (higher airflow) is required to cool a zone. Also, to maintain indoor air quality we want to maintain a minimum airflow, no matter what mode, to satisfy indoor air requirements (air changes). A fan speed might be lowered, or raised, depending on the condition of the zone compared to the programmed setpoints and needs for the zone.
We can further complicate the situation if we wanted to take into account outside conditions for economizer operation, humidity control, CO2, building pressure requirements, or other.
 
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