HVAC: Does closing ducts reduce a heating bill?

I thought it was a simple question, but I guess it's more complicated than I thought.

Backstory: our heating bill has been about $170 for the past two months we've been our new house. That is just the gas used by the heater and the water heater. Our electricity bill etc is another issue.

So! I did some poking around and found that the ducts hand vents in them for the basement. I closed those as I don't want my basement heated.

We also don't use our upstairs (yet) so I closed those registers too.

My heating bill is still $170 (but really, we did this right before the end of a billing cycle, so who knows what next month's is going to be...)

I e-mailed Puget sound energy to see if they'd tell me if this is the "normal" cost of gas for this house (in previous years) but noted in their reply was:

PSE said: Closing off the registers actually makes your system less efficient. If the system was designed properly then it is best to operate it with all the registers open. Closing registers doesn't allow enough return air to flow and can cause short cycling of the furnace, significantly reducing its life. In addition, closing the registers creates additional static pressure in the duct systems reducing the efficiency of the furnace and air handler.

Some internet research showed some people arguing for both sides of the story. Some say closing registers reduces the efficiency, some say it makes the heater more efficient...

What are the collective's thoughts?

Quick note: I did not close the one return air line in the house. It's big and in my dining room, and could not find any others that might be returns.

I thought registers were the returns and vents were the output?

Depends on how the system is controlled...if there's no temperature sensor in your basement and one on the main floor (most common setup I think), meaning basically that you're bleeding hot air into your basement for no good reason, then closing the vents (and registers, so your system only has to re-heat the warmest air) should reduce your heating bill.

Edit: Alright well leave all the registers open since it apparently causes too much intake restriction otherwise.

You're good. Your terminology is off. Don't close an inlet, that's what they were saying.

Gotcha.

So I closed "vents" not "registers" :)

My thinking was along the lines of "Gameboy's". Less rooms to heat = less money spent. But dang if this heating bill isn't killing me.

Just be happy you didn't have to do like I just did and order 200 gallons of propane at $3.90/gal

As someone who worked in the industry, a register is a grille with a damper attached. There are supply grilles and there are return grilles. There are also ceiling diffusers, which are supply devices.

Closing off supply registers in unused rooms will theoretically push more of the conditioned air into the rooms that have open supplies, but it won't make much overall difference. Also, your system fan is sized to move a specific amount of air at a given back-pressure. Varying too much from those parameters can cause some fans to enter an unstable area of operation, which would be um, bad.

everyone i know has always blocked off vents to rooms and levels that aren't being used to save money. i cut the heating bill at the last house i was renting by taping cardboard to the vents and return register in the upstairs of the house and shutting the door to the stairs to keep all the heat on the lower level where i was- but i kept the one vent in the basement open to keep air circulating thru it and keep the kitchen and bathroom floors upstairs warm.

It works as long as you can sufficiently close off those areas from the rest of the system. I have two bedrooms and a bath upstairs that doesn't get used, and I knocked my electric bill down significantly in the summer by closing vents and doors to the unused rooms. I also use ceiling fans year round pretty much which keeps the air in the house circulating better. Running the ceiling fans on reverse in winter allows me to set the thermostat like 4 degrees cooler and stay comfortable in the winter.

Karacticus wrote: Just be happy you didn't have to do like I just did and order 200 gallons of propane at $3.90/gal

Pfff, I just took delivery of 400 gallons of biofuel at $4.20 a gallon.

Close the top floor vents in the winter and open the bottom ones. Heat rises.

Do the opposite in the summer; cool air falls.

I won the gas bill argument last month by:

• Opening the basement vents and closing the vents in the non used rooms upstairs (single level 1800sf with full basement)
• Turning the water heater down from "Magma" to "Hothothothothot"
• Spraying the inner roof of our extension with expanding insulation
• Adding plastic to the windows on inside and outside

From $225 to $155 in one month

The plastic over the windows was my next idea but winter here is just about over (I figure one month left). I couldn't help but notice that the only separation between our basement and our living area was a hardwood floor. I'm thinking of tacking some insulation to the ceiling of the basement (floor of the living area).

I thought that'd help keep the heat in the living area (plus sealing the doors, etc)

Good times.

Don't worry about losing heat to the basement. You lose cooling down in the summer- the heat goes upstairs. Doors between levels improves comfort levels a lot, and allows you to keep a more consistent temp throughout the house.

Fix drafts, drop your thermostat setting a couple of degrees and buy snuggies.

The short cycling thing is more of an AC argument from what I understand. Running the AC for short cycles doesn't let the air circulate well and it doesn't get dehumidified by the system as efficiently leading to moist air. As far as heating goes, as long as you don't shut down so much flow that you create significant back pressure on the system, you should be fine. Your heater core is like a radiator in a way and you need a certain amount of air to flow over it to pull the heat away from it.

America.

Where people buy a house so large, they save money by not using rooms.

z31maniac wrote: America. Where people buy a house so large, they save money by not using rooms.

i suppose you have some sort of a point here?

the house i was renting wasn't "large"- it was a smallish turn of the last century house with 2 bedrooms upstairs and one bedroom and a bathroom in an addition that was added maybe 30 years ago. it also had an attached uninsulated 2 car garage that was added probably about when the addition was put in. the rent was ridiculously cheap- $300 a month- and i was all by myself. so i shut off the heat and all airflow to the upstairs during the winter months, which not only kept heat from being wasted but also provided a "buffer" of dead air between the downstairs where i lived and the -30 degree temps and 40mph winds that this area of the world is known for during the winter..

during the summer, i opened the door to the stairs and cracked all the windows upstairs and a few of them downstairs to give the heat somewhere to go... i only had to fire up the in wall AC unit a few times just to take the edge off the heat in the living room in the 3 summers i was there.

z31maniac wrote: America. Where people buy a house so large, they save money by not using rooms.

Maybe, but my parents used to restrict warm air flow to the upstairs of our house to save money and every room was slept in. We didn't live up there, we just slept up there so it didn't need to be so warm. I also change the airflow to various parts of my house depending on the season and whether we're heating or cooling and we have two people in every bedroom. Not every problem is over consuming Americans.

mazdeuce wrote:

z31maniac wrote: America. Where people buy a house so large, they save money by not using rooms.

Maybe, but my parents used to restrict warm air flow to the upstairs of our house to save money and every room was slept in. We didn't live up there, we just slept up there so it didn't need to be so warm. I also change the airflow to various parts of my house depending on the season and whether we're heating or cooling and we have two people in every bedroom. Not every problem is over consuming Americans.

Same here. My current house is ~1975 sq ft, I have a spare bedroom that's not used so it gets the vent shut off, that redirects the heated air to the rest of the house and thus saves me money. I've tinkered with the vents so the bedrooms stay a bit cooler than the rest of the house, also the original ductwork to the master bath is way oversized. So it has a homemade restrictor to keep it from getting too hot or, in the summertime, too cold. My fourth bedroom and third bath are in the freestanding garage, these rooms each have their own heat/AC which is turned off in the bedroom(since I only use it for storage) and as low as possible in the bath only to prevent freezing.

But don't let that stop you from feeling smug, z31.

z31maniac wrote: America. Where people buy a house so large, they save money by not using rooms.

Wow

You want to talk about jumpin in the Kool-Aid and not knowing the flavor...

Anyhoo, I went and priced insulation for the basement ceiling yesterday. I haven't taken an accurate account of what I'll need, but at about $50 for a 25-foot roll, I might have to pick at it over the summer as we have free cash. For now we'll just bite the proverbial bullet.

Thanks everyone.

A couple of physics considerations...

closing heat vents almost always reduces furnace efficiency. This usually leads to less heat in the house, but no less fuel used.

If you have enough flow through your other vents, it won't kill efficiency, however if you don't have a good way of blocking off the unheated rooms, it will all be for naught. The heat will rise, the cold will fall, and the net result is kinda pointless.

You are heating X amount of air

Reduce the amount, less heat required.

Curmudgeon wrote:

mazdeuce wrote:

z31maniac wrote: America. Where people buy a house so large, they save money by not using rooms.

Maybe, but my parents used to restrict warm air flow to the upstairs of our house to save money and every room was slept in. We didn't live up there, we just slept up there so it didn't need to be so warm. I also change the airflow to various parts of my house depending on the season and whether we're heating or cooling and we have two people in every bedroom. Not every problem is over consuming Americans.

Same here. My current house is ~1975 sq ft, I have a spare bedroom that's not used so it gets the vent shut off, that redirects the heated air to the rest of the house and thus saves me money. I've tinkered with the vents so the bedrooms stay a bit cooler than the rest of the house, also the original ductwork to the master bath is way oversized. So it has a homemade restrictor to keep it from getting too hot or, in the summertime, too cold. My fourth bedroom and third bath are in the freestanding garage, these rooms each have their own heat/AC which is turned off in the bedroom(since I only use it for storage) and as low as possible in the bath only to prevent freezing. But don't let that stop you from feeling smug, z31.

Not smug at all (at least about this topic )

I just find the situation an interesting juxtaposition is all.

interestingly enough I was watching This Old House this weekend and a related topic came up.

They were doing a review/install of an automatic zoning, multi thermostat system in a house. Basically there's dampers that open/close ducts to upstairs or downstairs or rooms or whatever based on the need there with these things:

I thought.. huh.. what if only one zone needs heat, won't that hurt the blower motor fan like GRM suggested? ...and sure enough they answered that question. Yes, the fan gets out of efficiency with too much resistance, which causes premature failure, and leads to inefficiency in operation. The solution?... they install a weighted bypass on the main output duct, and vent it back into the return line. (technically called a 'forced air bypass damper')

Pretty simple, and pretty slick backpressure solution. Keeps the blower fan from experiencing too much backpressure, and pre-heats the "waste" return air to reduce run time for whatever zone it's warming at the time.

Now a zone equalizing setup probably is based more on comfort than a "keep costs down" solution, but I found it interesting they addressed the backpressure concern and installed an HVAC blowoff valve or waste gate. Ha.

We closed the returns in both spare bedrooms but left the outlets open. The rooms stay warmer and the furnace runs less. In fact, last month's electric bill was only $379 and January/December was the coldest months we've had on record in over 20 years. This time last year that same bill was over $420.

House is total electric.