Higher than normal Electricity bills caused by my mistake

Geo NR Gee · 03-01-17, 03:13 PM

For the last three or four months, my electricity and gas bill has been about $250 and above and about $100 more than normal. We've stopped long ago using the electric dryer and hang dry our clothes. We make sure to shut off the TV when not in use. We turn off the parasitic devices like stereos and unplug anything that is not in use. What is going on?

I finally figured it out.......

8 months ago, I closed the vent in the workout room because you don't want it hot when you are getting hot. Right?
1 of 13 vents closed

Then it was the laundry room vent because it is such a small room and there was boxes put on top of it anyway.
2 of 13 vents closed now

The guest bathroom vent next to the thermostat was keeping the bathroom too hot (and maybe the thermostat?), so that vent was closed
3 of 13 vents closed

Our 4 bedroom house is now empty since the boys have all graduated from college, got jobs and moved out. With just the two of us and the dog, I thought it would be a good idea to close the doors to their bedrooms and what the heck close the vents and just not heat the unused space. Bad idea.
5 of 13 vents closed or 38.46%.

The heat pump seemed to run longer and longer, but I wasn't sure if it was the cooler 20*f weather? Puzzled still... I checked the filter as normal and one night heard that the sheet metal on the air handler would pop once when the fan started and when it stopped. There was my moment of clarity.

I didn't even think about the restrictions to the airflow across the coils. The popping stopped and the heat pump did it's job and now the house is warm and the heat pump doesn't come on as much now!

What is in fact happening that causes the heat pump to keep running exactly?

I did some google searches and found some information here
Can You Save Money by Closing HVAC Vents in Unused Rooms?

MN Renovator · 03-01-17, 05:06 PM

Less airflow over the coil will cause a few things to happen.

1. The temperature rise over the coil will be higher because less heat is being carried away from the coil.
2. The higher temperature rise is less efficient, especially with a heat pump system because the higher the temperature difference, the more wattage the compressor is pulling. Non-condensing furnaces are also less efficient because more heat is lost up the flue since less is being captured. Condensing systems still lose some efficiency, but not as much. With condensing furnaces, if the air flow gets cut off too much, it will no longer reach a condensing temperature which will cause the efficiency to plummet and run the risk of melting the plastic exhaust pipe, there are temperature limit switches in place designed to prevent that from happening.
3. The lower airflow means less heat transferred to the living space, keep in mind that as temp rise over the coil increases, the heat pump loses capacity as that temperature rise occurs. CFM*(temp rise*1.08)=BTU output.
4. Defrost cycles will increase with the increased runtime and temperature rise.

So basically your system is putting out less heat over time, running longer, and consuming significantly more power for the same amount of total heat needed in the process. Heat pump systems need the amount of airflow from the install specifications to get their rated efficiency and output. The same applies to air conditioning too, without the proper airflow temperature drop is increased, capacity and efficiency are also lost and there is a risk of the indoor coil freezing and liquid returning to the condenser and slugging the compressor.

jeff5may · 03-03-17, 12:14 PM

OK, so we have acknowledged a few trends here:

1. Most "casual" users believe that closing vents increases energy efficiency.

2.Most residential duct systems are already correctly sized for the unit.

3. Heat pump and condensing furnace systems work close to the same as "blast" furnace systems.

The truth is that none of these beliefs are true. No matter how you slice it, cutting down an already restricted system doesn't help. However, it is a good way to inadvertently destroy a heat pump: bursting freon pipes and burnt compressors come to mind. Besides not saving energy in the short term, due to the heat escaping through leaky ductwork (worse than heating/cooling an unwanted zone), the added stress on system components shortens its useful lifespan.

What hasn't been touched here is this: what if you INCREASE the airflow in these types of high-efficiency systems in the zones that more capacity is desired? For instance, installing a larger vent in the master bedroom and the kitchen. Or maybe installing a "duct booster" fan to send added comfort to a desired zone. Would the additional airflow help out energy efficiency? I believe if the if the change was made skillfully, it could do lots of good for not much effort or expense.

Geo NR Gee · 03-04-17, 12:04 AM

What should the speed of the airflow be across the coils or even at the vents? Is there a standard speed?

I noticed that one bedroom that has the most windows in the house is the coldest and is the last ducting on the run. It doesn't blow as much and is a lot cooler. I checked for leaks in the duct under the house, but didn't find any. It would be a good candidate for the inline fan.

jeff5may · 03-04-17, 11:44 AM

The rule of thumb is 400 CFM per Ton of capacity for "regular" systems and 500 CFM per Ton for "heat pump" or "high sensible heating" applications. The air handler of your system should have the specs right on the nameplate and/or data tag. Most residential systems are rated at 1/4 inch water column (or less) static pressure, and max pressure is specified around 1/2 inch of discharge pressure. If you desire more info, the installation manual for the specific model has charts and lookup tables to aid techs in assuring high performance.

Before doing mods on the existing system, I would definitely recommend taking measurements on the existing setup. There are two pieces of test equipment needed: a manometer and an anemometer. The manometer measures pressure, the anemometer mesures airspeed. Both can be found online for under $20 (shipped) each.

I use a RadonAway #50017 u-tube manometer and an anemometer/thermometer like the GM816. I know, I know, they're cheap. But so am I, and they work fine for me. Feel free to spend more on instrumentation if you like.

Ron342 · 03-07-17, 11:27 AM

This is good stuff, guys and yes i confess to closing ducts thinking i was saving kilowatts.
But Jeff how do you use the flow meter - string it up against the evaporator coils and close up your access hole for the reading? And i assume you just tap a hole in the discharge plenum for the pressure?
Another very common problem with low air flow, poor performance, tripping high pressure cutouts, and cooked compressors is caused by simple crud buildup on the evaporator. Most of us just change filters but think that keeps the evap clean - not necessarily guys - always get a look at it every couple of years - some are so bad they have to be removed to clean. Much of it is , i think, mold type growth on dust that builds during the wet summer use and then cooks hard in winter at least on heat pumps. Don't ask how i know!
You can buy a very thin fiber optic viewing snake for about $15 to use with your phone - works great for those areas you can't easily see!

jeff5may · 03-07-17, 01:09 PM

To use the anemometer you simply hold it in an air stream and read the airspeed. To find CFM or M3/min, you have to calculate it. Airspeed times cross section area equals volume. The gizmo is awesome for balancing flow at registers also.

03-01-17, 03:13 PM	#1
Geo NR Gee Journeyman EcoRenovator Join Date: Jan 2011 Location: Seattle Posts: 326 Thanks: 109 Thanked 23 Times in 18 Posts	Higher than normal Electricity bills caused by my mistake For the last three or four months, my electricity and gas bill has been about $250 and above and about $100 more than normal. We've stopped long ago using the electric dryer and hang dry our clothes. We make sure to shut off the TV when not in use. We turn off the parasitic devices like stereos and unplug anything that is not in use. What is going on? I finally figured it out....... 8 months ago, I closed the vent in the workout room because you don't want it hot when you are getting hot. Right? 1 of 13 vents closed Then it was the laundry room vent because it is such a small room and there was boxes put on top of it anyway. 2 of 13 vents closed now The guest bathroom vent next to the thermostat was keeping the bathroom too hot (and maybe the thermostat?), so that vent was closed 3 of 13 vents closed Our 4 bedroom house is now empty since the boys have all graduated from college, got jobs and moved out. With just the two of us and the dog, I thought it would be a good idea to close the doors to their bedrooms and what the heck close the vents and just not heat the unused space. Bad idea. 5 of 13 vents closed or 38.46%. The heat pump seemed to run longer and longer, but I wasn't sure if it was the cooler 20*f weather? Puzzled still... I checked the filter as normal and one night heard that the sheet metal on the air handler would pop once when the fan started and when it stopped. There was my moment of clarity. I didn't even think about the restrictions to the airflow across the coils. The popping stopped and the heat pump did it's job and now the house is warm and the heat pump doesn't come on as much now! What is in fact happening that causes the heat pump to keep running exactly? I did some google searches and found some information here Can You Save Money by Closing HVAC Vents in Unused Rooms?

03-03-17, 12:14 PM	#3
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	OK, so we have acknowledged a few trends here: 1. Most "casual" users believe that closing vents increases energy efficiency. 2.Most residential duct systems are already correctly sized for the unit. 3. Heat pump and condensing furnace systems work close to the same as "blast" furnace systems. The truth is that none of these beliefs are true. No matter how you slice it, cutting down an already restricted system doesn't help. However, it is a good way to inadvertently destroy a heat pump: bursting freon pipes and burnt compressors come to mind. Besides not saving energy in the short term, due to the heat escaping through leaky ductwork (worse than heating/cooling an unwanted zone), the added stress on system components shortens its useful lifespan. What hasn't been touched here is this: what if you INCREASE the airflow in these types of high-efficiency systems in the zones that more capacity is desired? For instance, installing a larger vent in the master bedroom and the kitchen. Or maybe installing a "duct booster" fan to send added comfort to a desired zone. Would the additional airflow help out energy efficiency? I believe if the if the change was made skillfully, it could do lots of good for not much effort or expense. Last edited by jeff5may; 03-05-17 at 12:18 PM..

03-07-17, 11:27 AM	#6
Ron342 Apprentice EcoRenovator Join Date: Feb 2010 Location: Maryland Posts: 120 Thanks: 26 Thanked 12 Times in 8 Posts	Lost in the ductwork? This is good stuff, guys and yes i confess to closing ducts thinking i was saving kilowatts. But Jeff how do you use the flow meter - string it up against the evaporator coils and close up your access hole for the reading? And i assume you just tap a hole in the discharge plenum for the pressure? Another very common problem with low air flow, poor performance, tripping high pressure cutouts, and cooked compressors is caused by simple crud buildup on the evaporator. Most of us just change filters but think that keeps the evap clean - not necessarily guys - always get a look at it every couple of years - some are so bad they have to be removed to clean. Much of it is , i think, mold type growth on dust that builds during the wet summer use and then cooks hard in winter at least on heat pumps. Don't ask how i know! You can buy a very thin fiber optic viewing snake for about $15 to use with your phone - works great for those areas you can't easily see!

03-01-17, 05:06 PM	#2
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 940 Thanks: 41 Thanked 117 Times in 91 Posts	Less airflow over the coil will cause a few things to happen. 1. The temperature rise over the coil will be higher because less heat is being carried away from the coil. 2. The higher temperature rise is less efficient, especially with a heat pump system because the higher the temperature difference, the more wattage the compressor is pulling. Non-condensing furnaces are also less efficient because more heat is lost up the flue since less is being captured. Condensing systems still lose some efficiency, but not as much. With condensing furnaces, if the air flow gets cut off too much, it will no longer reach a condensing temperature which will cause the efficiency to plummet and run the risk of melting the plastic exhaust pipe, there are temperature limit switches in place designed to prevent that from happening. 3. The lower airflow means less heat transferred to the living space, keep in mind that as temp rise over the coil increases, the heat pump loses capacity as that temperature rise occurs. CFM(temp rise1.08)=BTU output. 4. Defrost cycles will increase with the increased runtime and temperature rise. So basically your system is putting out less heat over time, running longer, and consuming significantly more power for the same amount of total heat needed in the process. Heat pump systems need the amount of airflow from the install specifications to get their rated efficiency and output. The same applies to air conditioning too, without the proper airflow temperature drop is increased, capacity and efficiency are also lost and there is a risk of the indoor coil freezing and liquid returning to the condenser and slugging the compressor.

03-04-17, 12:04 AM	#4
Geo NR Gee Journeyman EcoRenovator Join Date: Jan 2011 Location: Seattle Posts: 326 Thanks: 109 Thanked 23 Times in 18 Posts	What should the speed of the airflow be across the coils or even at the vents? Is there a standard speed? I noticed that one bedroom that has the most windows in the house is the coldest and is the last ducting on the run. It doesn't blow as much and is a lot cooler. I checked for leaks in the duct under the house, but didn't find any. It would be a good candidate for the inline fan.

03-04-17, 11:44 AM	#5
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	The rule of thumb is 400 CFM per Ton of capacity for "regular" systems and 500 CFM per Ton for "heat pump" or "high sensible heating" applications. The air handler of your system should have the specs right on the nameplate and/or data tag. Most residential systems are rated at 1/4 inch water column (or less) static pressure, and max pressure is specified around 1/2 inch of discharge pressure. If you desire more info, the installation manual for the specific model has charts and lookup tables to aid techs in assuring high performance. Before doing mods on the existing system, I would definitely recommend taking measurements on the existing setup. There are two pieces of test equipment needed: a manometer and an anemometer. The manometer measures pressure, the anemometer mesures airspeed. Both can be found online for under $20 (shipped) each. I use a RadonAway #50017 u-tube manometer and an anemometer/thermometer like the GM816. I know, I know, they're cheap. But so am I, and they work fine for me. Feel free to spend more on instrumentation if you like. Attached Thumbnails Last edited by jeff5may; 03-05-17 at 12:27 PM..

03-07-17, 01:09 PM	#7
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	To use the anemometer you simply hold it in an air stream and read the airspeed. To find CFM or M3/min, you have to calculate it. Airspeed times cross section area equals volume. The gizmo is awesome for balancing flow at registers also.