Shop Heating Question that is baffling me beyond belief!

[David Cramer]

Hello

I am very new to the Creek and have a shop heating question that I can't get a straight answer to.

A lot of guys keep their shop at let's say, 50 degrees, and then turn it up to, let's say 65 degrees when they are going to actually be out there to work.

I asked a friend, what's the difference between just keeping it at 65 and have it go on and off by itself when needed to maintain 65, versus turning it down to 50 degrees and then have it work hard for a long time to get to 65. Aren't they equal and if so, why not?

If it cycles naturally to maintain 65, doesn't that amount of natural gas equal to........... the gas it takes to maintain at 50 and work hard straight for the amount of time it takes to increase 15 more degrees?

I know I am wrong, but I just don't know why. They seem like they'd be even. Any heating experts who would care to explain the reasoning, I'd be more than grateful!!! My neighbors don't know either and everyone I've spoken to is split on it, but I've yet to ask a heating professional what the true answer is.

Thanks a lot! Great site ya have here people! Not much bickering to speak of. Unheard of on most woodforums I've checked out. Someone is doing something right. Keep it up!!!

Dave

p.s. How can Missouri get more snow, :eek: WAY more snow, than Ohio/Michigan? Elni-who-no:rolleyes: ?

[David G Baker]

Dave,
I have a 30x40 well insulated pole barn that is heated with a natural gas fired 75,000 BTU Hot Dawg heater. I do not work in the barn too often but store many things that I do not want to freeze so I keep the thermostat set at around 50. When I work in the building I turn the heat up to around 65. The heater comes on and stays on for around 15 minutes. I dress warmly because I am in and out of the building frequently. The temperature in Mid Michigan has been in the teens to twenties at night for the past week or so. During the day when I am in the building it has been in the mid to high twenties and the heater does not come on very often. I would say that it comes on about once every 30 minutes.
The way I have been using my heater has been very comfortable. My average monthly gas cost for the barn is around $30. I will probably never keep the heat at 65 degrees 24/7 so I can't tell you the cost difference.
David B

[Kyle Kraft]

I do the same thing. 50 degrees when I'm away and 60-65 when I work. Same as Dave about $30 more to heat the shop...where else can you get so much bang for the buck? Plus my machinery loves it!! Especially when we get a 60 degree day and 150% humidity in March.

[Todd Tolhurst]

Does it take more energy to keep your oven at 375 degrees constantly, or to only turn it on when you want to cook a frozen pizza?


Whenever you heat your space, heat will escape. The greater the difference between your heated space and its surroundings, the greater the heat loss. If you keep the heat low when you're not using the shop, you minimize the heat loss. The amount of heat lost from a 65 degree shop for many hours or days of idle time far exceeds the amount of heat needed to warm the shop from the 50 degree idle temperature to 65 degrees.

[Dick Strauss]

David C.,
The amount of heat lost to the outside is based on the temperature differential (the differnce between the inside and outside temps). Time also factors into the equation but is less significant. If you have a higher differential, you get greater losses. So a 50* garage will lose less heat to the atmosphere (at say 30*) than a 65* garage.

By turning it down to 50* you'll lose heat based on a temp diff of 20* for 90% of the time and 35* for 10% of the time instead of 35* for 100% of the time

This is the reason energy companies ask you to turn down your thermostat during Winter (closer to the outside temp) and up for Summer (closer to outside temp).

[John Schreiber]

I've heard this argument before, once even from an HVAC repair man. I'm not a heating expert, but I'll write down how I think it works and please tell me if it makes sense.

If your outside temperature is 30 and you are setting your shop thermostat to 30, you wouldn't use any energy to heat your shop.

If the outside temp stays at 30 and you set the thermostat to 35, you'll have to use a little energy to keep your shop temperature 5 degrees above the outside temperature.

If again the outside temp stays at 30 and you set the thermostat to 70, you will have to use a lot more energy to keep the 40 degree temperature differential between inside and outside.

So far this is obvious. If you aren't ever going to change the temperature in your shop, the lower you keep the thermostat, the less energy you are going to use. This is because the energy required for heating a given space (everything else being equal) is dependent on the difference in temperature between the inside and the outside. When there is a large difference between inside and outside, you lose more heat and you have to use more energy to keep the building warm..

Now, if you go out to the shop once a week and change the thermostat from 35 to 70, you will have saved a lot of energy not keeping the shop as warm all week. If you go out every day and raise the temp to 70, but set it down to 35 when you aren't there, then there is still a long period when little energy is needed to maintain the difference in temperature between the inside and the outside. If you were to go out to the shop every hour and turn the thermostat up to 70, then when it reached 70, you were turn the thermostat back down to 35; then come back to turn it back to 70 at the next hour, you would still be using less total energy than if the shop stayed at 70 the whole time.

So no matter how you slice it, I think you come out well ahead, from an energy use point of view at least, by turning down the temperature as much as is safe when you aren't using the space.

Make sense, or am I confused?

[David Rose]

OH! And don't forget that most "yellow" glues need their required temps until they FULLY setup. Otherwise they will chalk, which isn't good.

My zoned Train unit for the house will not let us set low temps below 65 or highs in summer above 50. I asked the installer why and he said what some of the others here have said. Somewhere around 7 to 10 degrees is the point where diminishing returns take place in a well insulated building. In other words, it takes more BTUs to move more than 7 degrees than it does to keep the temp all day and night. I still would like to go below 65 on winter nights. But maybe in a couple of years they will change their minds, and I can reprogram for lower lows. ;-)

David

[Brian Hale]

........... I still would like to go below 65 on winter nights. But maybe in a couple of years they will change their minds, and I can reprogram for lower lows. ;-)

David

Keep a candle burning under your thermostat :rolleyes:

Brian :)

[Perry Holbrook]

As an ex-energy engineer I often found it hard to convince building owners why they should set back their heat t-stat and night. For some reason they thought it made common sense if you left it set at a constant temp it cost less than turning it down and back up.

Unfortunately, thermodynamic laws are not based on common sense. John explained it pretty well.

One thing that makes this a llittle more complex is thermal mass. Most shops have concrete floors and a lot of heavy equipment. Both are heat sinks and will cool down and heat up slower than the air. If the temp is allowed to drop too low, the thermal masses fall to ambient temp and will continue to cool the air for some period of time even after the air has heated up.

The energy calculations get much more complicated when this thermal mass is considered. My guesstimate is for my shop a night time temp of 50 is about right day time 68. I have an automatic t-stat that does it for me but remember I'm in the shop 12 hrs/7days.

Perry

[Dick Aubochon]

As an ex-energy engineer I often found it hard to convince building owners why they should set back their heat t-stat and night. For some reason they thought it made common sense if you left it set at a constant temp it cost less than turning it down and back up.

Unfortunately, thermodynamic laws are not based on common sense. John explained it pretty well.

One thing that makes this a llittle more complex is thermal mass. Most shops have concrete floors and a lot of heavy equipment. Both are heat sinks and will cool down and heat up slower than the air. If the temp is allowed to drop too low, the thermal masses fall to ambient temp and will continue to cool the air for some period of time even after the air has heated up.

The energy calculations get much more complicated when this thermal mass is considered. My guesstimate is for my shop a night time temp of 50 is about right day time 68. I have an automatic t-stat that does it for me but remember I'm in the shop 12 hrs/7days.

Perry

Perry,
That was my thinking as well. What about the energy expenditure to reach thermal equillibrium? That is a factor with all the cast iron, steel, etc. in the shop is it not? I still think the idea of a set back is a good one. My shop is in an outbuilding garage that was built about 60 years ago, so you can imagine how loose the building is. I leave my heat at 50 deg F almost all the time, except when I have a glue up, or a finish drying.

[Mike Cutler]

Heck.. I'd be happy just to get the shop to 50 degrees. It's about 16 deg. in there right now.

It all comes down to how many calories, or BTU's it takes to get the room back up to temperature, versus how many does it take to keep it at a given temperature.
You're better off setting the temp back when not in use, just don't have a huge delta, or you expend more energy than you save bringing it back up to temp.
While on this subject. It may be worthwhile to check out the newer generations of Smart Temp controllers. It's not just on/off anymore. The controllers are actually self tuning PID ( Proprotional+ Integral+Derivative) controllers. Very nice little units.

[Al Willits]

Honeywell has done extensive work on set back thermostats, maybe visit their web site and take a look.
But there does seem to be a point where if the differential is to great, the cost to bring a house/garage/shop back to temp negates the savings.
I don't remember exact numbers and it might vary with climate conditions, (web site talks about this I believe) but seems to me the 10-15 degree number comes up a lot.
I only need to deal with Minn so I don't remember the varied setbacks, but I think the website has a chart for different parts of the country.

fwiw some of the new multi stage furnaces don't recommend setting back at all, others run a 2 stage thermostat which runs on the low fire mode till heating requirements are greater than the lower input can handle, then switch over to a higher input.

Al...who's kinda a HVAC guy...imho

[Ken Garlock]

The whole problem is also modulated by the amount of insulation surrounding the volume you are heating/cooling. Insulation is cheap, use a lot of it.

With good insulation, the room will cooler slower and heat faster in the winter, and the reverse in the summer.

[Kurt Strandberg]

I have a 30X40 pole building with 9' ceiling and I have a 75,000 btu hanging unit, I keep it at 45º when I am not in there and when I am going to work in there, like today, I turn the heat up to about 70º untill it shuts off then I turn it down to about 55º for the rest of the time I am out there.

I also have the thermostat at about 7 feet of the floor.

[Robert Mickley]

its a moot point in my shop, it gets s warm as the fire will make it. :D

So to sum it up there are several factors
How goos your insulation
How much iron is in the shop.

Personally If I ever get around to doing a new shop, I'm going with a heated floor, lots of insulation, good windows and doors and I'm leaving the temp set at the same place all the time. I build a fire in the shop every morning. Even on days like today when I've only been out there maybe an hour so far today. When I walk in I want it warm

[Frank Chaffee]

Comfort level and fuel efficiency have been covered very well here, but how do temperature swings affect wood stored and in various stages of construction in the shop?

[David Cramer]

Thanks so much for the great advice. It really did help. My question of it taking so long to gain that 15 degrees versus it being set and cycling when needed was definitely answer.

One poster (Al I believe) said the cost to bring a shop back up to temp negates the savings. The differential is too great. That is the unknown to me, at what point do you save and at what point are you gaining nothing by keeping it down. That actually was the heart of my question, and there are obviously a lot of variables that must be taken into consideration to answer that question. You all have opened me up to those variables that I hadn't thought:rolleyes: of.

I REALLY :) appreciate all the indepth and well thought out responses.

THANKS!!!!

Dave

p.s. Sorry I didn't say thanks sooner. I don't get time to be on the computer everyday.

[Ron Wessels]

People still seem to be having trouble intuitively grasping that the energy required to re-heat a shop is less than the energy required to keep it heated in the first place (for short durations, anyway).

Think of the following analogy. You have a bucket containing evenly spaced holes all along the sides. The higher the bucket is filled with water, the more holes the water will leak out of, therfore the greater the rate of water leakage. Now, which uses more water: keeping the bucket filled or re-filling the bucket when required?

If you think about it for a bit, you will realize that the amount of water taken to re-fill the bucket is always less than the amount of water taken to keep it filled.

[David Cramer]

Hey thanks Ron, EXCELLENT:) analogy. You put it rather well.

Dave

[Tyler Howell]

I have a 30X40 pole building with 9' ceiling and I have a 75,000 btu hanging unit, I keep it at 45º when I am not in there and when I am going to work in there, like today, I turn the heat up to about 70º untill it shuts off then I turn it down to about 55º for the rest of the time I am out there.

I also have the thermostat at about 7 feet of the floor.

Help me out Pro's, but I think this is where the extra money is spent.
Ambient temps don't rise any faster if you over shoot your desired goal, 55* in this case. It is best to set the temp for the target.

As Ken said your cheapest investment is insulation, windows and wheather stripping, Often overlooked in shop space.

[David Cramer]

You hit the nail on the head Tyler! Another great :) observation. I will be putting R26 in my ceilings, when I get there. The brain juices are flowing now with all these different ways of looking at it.

Dave

[Al Willits]

Spent 35 minutes on the honeywell site and gave up, here is something we have at work though, can't remember where it came from though.

Might add that with today's multi staging furnaces, the "funaces only put out one level of heat" is wrong.

""""
A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings.
This misconception has been dispelled by years of research and numerous studies.
The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature.
You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the
longer your house remains at the lower temperature, the more energy you save.
Another misconception is that the higher you raise a thermostat, the more heat the furnace will put out, or that the house will warm up faster if the thermostat is raised higher.
Furnaces put out the same amount of heat no matter how high the thermostat is set--the variable is how long it must stay on to reach the set temperature.
In the winter, significant savings can be obtained by manually or automatically reducing your thermostat's temperature setting for as little as four hours per day.
These savings can
be attributed to a building's heat loss in the winter, which depends greatly on the difference between the inside and outside temperatures.
For example, if you set the temperature back on your thermostat for an entire night, your energy savings will be substantial.
By turning your thermostat back 10 degrees F to 15 degrees F for 8 hours, you can save about 5% to 15% a year on your heating bill -- a savings of as much as I% for each degree if the setback period is eight hours long. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates.
Save 25 percent of your heating bill by turning the thermostat down from 70 to 65 degrees while awake and down to 60 or 55 degrees while sleeping or away.
It's an myth that rewarming a house after turning down the thermostat takes the same amount of heat that was saved. The truth is that the bigger the difference between the indoor and outdoor temperature, the more heat escapes your house. Lowering the thermostat decreases the difference and you lose less heat.
Chuck Seipp, energy analyst with Arrowhead Economic Opportunity Agency, recommends keeping the thermostat turned down to within IO degrees of the original setting. Some efficiency is lost when the difference is greater than 10 degrees, he says.
A hot water faucet leaking one drip per second pours 3,120 gallons of hot water and $35 a year in energy costs down the drain. The fix is usually a cheap washer or, in newer washerless faucets, a drop-in cylinder.

[PeterTorresani]

Scientifically:
q=-k*A*(Ti-To)

The answer to this question is not as complicated as many people have made it. As stated in a couple posts, the amount of heat lost is directly proportional to the temperature difference across the barrier (wall/door/window).

In my mind (twisted as that may be) the easiest way to understand it is to realize that over time, you only pay for the heat that leaves the building. Therefore, as the inside temp goes up you lose more heat and pay more money.

This is true regardless of the time at the high or low temperature, the magnitude of the offset used, the thermal mass of the contents, or the amount of insulation. Some of these factors affect the magnitude of the difference, but it always saves heat to turn down the temp. No ifs, but, excepts, maybes, provisos, or what ifs. ALWAYS

FWIW: The science behind this isn't thermodynamics. It's heat transfer. Related, but completely different.

[Stephen Clem]

Quick side question from a new Woodworker. How long does it take for yellow wood glue to set? I need to know since I'm building a cradle for my soon arriving baby, and didn't think about keeping the shop warm for the glue. So basically, what's the minimum temperature and time required to allow the glue to set well enough? Thanks!
Stephen
P.S. I'll be sure to post pictures of the cradle (and baby).

[Dan Gill]

With a little ingenuity you don't have to keep your whole shop warm to let the glue set. Simply put an electric blanket over the cradle.

Then you go back inside and apologize to your wife for getting sawdust on the electric blanket. :D