over slab heat in basement argument
Talisker2
| Posted in Energy, Heating & Insulation on
My son in law says he read someplace that there is a electric element (resistance) heat coils that can operate cheaper than hotwater in pex in a builtup floor over a uninuslated slab. I told him he was full of it. Was I wrong? He claims that this electrical system pulse’s the power on and off and some how uses less energy. He claimed that even though I have a boiler and zones to the room baseboards that the electric would be cheaper. I think sometime he only understands a little bit of the information and gets some wild idea that it is the end all for heating. I tried to tell him that a watt is a watt and electricity is still more expensive than natural gas boiler. (WeilMclain Gold abt. 85% eff.)
Thanks in advance.
Jim
Replies
Electricity is "near if not" 100% eff at turning power into heat.
You hit the nail on the head - what is the cost of elec vs gas?
Not sure how accurate these numbers are, just pulled them off the web. Electricity is .099 per kwh, natural gas is .121 per therm. Electric is poised to go to 2c per kwh soon. (double?) Not sure when but as the gas fields that locally supply the city and South Central AK are rapidly depleting and that is what fires the turbines for the electricity.
1 kWh is equal to 3,413 BTU/h, and there are 100,000 BTU/h in a therm of natural gas.So, using your energy rates, your son pays ~24 times as much for EL heating as he does NG heat. BTW- did you mean $1.21/therm?About the only time that EL heat is cost effective is when you're using a heat pump and the heat source (whether it be the ground, air, or something else) is warm enough. You can sometimes get 15,000 BTU/h of heating from a heat pump with an input of only 3,413 BTU/h (1 kWh).When using EL resistance heat, the efficiency is 100%, but no more. Heat pumps can be 500% efficient (I know, that sounds wrong, but it's true) so they make up for some of the difference in EL and NG prices.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Sorry got the numbers twisted around. Local is .121 per kwh and .449 per therm.
Jim
Sorry got the numbers twisted around. Local is .121 per kwh and .449 per therm.
Then the electric heat costs you $3.51 per therm, which is 6.6 times as much as gas at 85% efficiency.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
You are correct in questioning your son in law. You generally will not magically increase your efficiency of your use of energy by 'pulsing' it on/off. I've been in the energy consulting business for almost 30 years, now. That sounds like snake oil to me.
BTW at the prices and gas efficiency you quoted, electricity costs just over $35/MBtu and gas at just over $5/MBtu ... i.e. you pay 7 times as much for electric heating than you do gas ... even w/ the inefficiency of gas combustion. The pulsing would have to reduce run times by over 7 times to just break even. A salesman has gotten a hold of him ... check him into Betty Ford pronto. Have him sent back for regrooving. And get a hold of that salesman and run him out of town on a rail. OK ... just kidding (a little).
1 kWh is equal to 3,413 BTU/h, and there are 100,000 BTU/h in a therm of natural gas.
Actually 1 kWh is equal to 3,412 BTU, and 1 kW is equal to 3,412 BTU/hr.
And a therm is 100,000 BTU, regardless of the energy source.
When using EL resistance heat, the efficiency is 100%
You're the second person who claimed this. While it's true that - at the point of use - electricity can be converted 100% into heat, it's no more than 30% efficient from source to use, which is why it tends to be so expensive.
For some end uses, like incandescent lighting (which Amory Lovins described as a space heater that also happens to give off some light), it is only 5% efficient.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 12/31/2008 12:47 am ET by Riversong
3412 ... 3413 .... dude ... you're splitting hairs. Unwarranted, really.
And no one (i.e. very few) uses the inefficiency of electric generation back at the power plant to calc energy at the building envelope. While your point is appreciated, you can't really calc the 33% efficiency of generation ... then you would also have to calc the production cost of the coal going into the power plant, etc. etc. (not to mention the infrastructure cost of the natural gas piping). Since what you pay already accounts for the inefficiency of the generation, my economic analysis must start at the meter. That is the principle reason why electricity cost is so high ... it uses e.g. the gas to convert/generate/transport electricity to your house. All kinds of losses there.
It is impractical to carry our evaluation past the point of metering and the cost that we pay for each metered unit.
Every watt of EVERY light bulb ends up as heat ... whether incandescent or fluorescent or LED. Some lamps produce light more efficiently, that's all.
3412 ... 3413 .... dude ... you're splitting hairs. Unwarranted, really.
You didn't read the equations. JonBlakemore said that:
1 kWh is equal to 3,413 BTU/h
A kWh is a volume of energy and is equatable to BTUs.
A kW is a rate of energy transfer (power) and is equatable to BTU/hr.
And no one (i.e. very few) uses the inefficiency of electric generation back at the power plant to calc energy at the building envelope... It is impractical to carry our evaluation past the point of metering and the cost that we pay for each metered unit.
And that's the crux of the problem. If it's impracticle to consider that the reason we pay so much for electricity (most of us) is that it is a phenominally inefficient way to use fossil fuels, then we are going to soon discover the price shock of the end of cheap and available stored energy.
If we don't consider the broader impacts of our energy choices, often distorted in the market by massive government subsidies (your tax dollars being squandered), then we will find ourselves in a massive crisis of our own making.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 12/31/2008 11:21 am ET by Riversong
Edited 12/31/2008 11:36 am ET by Riversong
Edited 12/31/2008 11:36 am ET by Riversong
Also, actually gas can vary in Btu content. Where I'm at, I understand that gas can end up a mixture depending on demand, availability, etc. ... so there may be variations in gas value that may be greater than the 0.029% variation in the Btu/kwh that you corrected the other posters on.
That's why they price gas in therms -- the quantity in a therm is adjusted based on the energy content of the gas.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
"hat's why they price gas in therms -- the quantity in a therm is adjusted based on the energy content of the gas."Except where they don't.Lots of places price in CCF (100 cubic ft)..
William the Geezer, the sequel to Billy the Kid - Shoe
Yes, but in the bill they have an "energy adjustment factor" or some such.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Not really.Just the cost of gas. But that is adjusted up to 4 times a year with the approval of the state.But it is a mix of stop purchased gas, long term contracts, and summer gas that was stored.So there the energy rating might be included, but it is about 5 levels deep..
William the Geezer, the sequel to Billy the Kid - Shoe
Well, your PUC isn't on the ball, then. There should be an adjustment factor for the gas energy content.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
"Actually 1 kWh is equal to 3,412 BTU, and 1 kW is equal to 3,412 BTU/hr."
You're right, I got energy and power mixed up.
I do notice that you use 3.412 as the factor, which I've seen others use before. I've learned that it was 3.413 and can find many sources that both agree and disagree with me. Why is that?
Jon Blakemore RappahannockINC.com Fredericksburg, VA
I do notice that you use 3.412 as the factor, which I've seen others use before. I've learned that it was 3.413 and can find many sources that both agree and disagree with me. Why is that?
Because it depends on which BTU you use.
thermochemical Btu
1 Btu = 1054.35
J
59 °F (15 °C) Btu
1 Btu = 1054.80
J
International Table Btu
1 Btu = 1055.06
J
mean Btu
1 Btu = 1055.87
J
the IT unit is the one used in DOE/EIA publications.
Since 1055.06 Joules = 0.29307 watthour
and 1 kWh = 1/0.29307 x 1000 = 3412.15 BTU
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Again, who cares? There is only an error of 0.029% .... under 3 hundredths of a percent between the two. This ain't rocket science guys. We are simply trying to do some rough conversions/comparisons. Discussing the fine points of the difference is relatively pointless.
Again, who cares? There is only an error of 0.029% .... under 3 hundredths of a percent between the two. This ain't rocket science guys. We are simply trying to do some rough conversions/comparisons. Discussing the fine points of the difference is relatively pointless.
JohnBlakemore cares. He asked a question and I answered it. I never claimed that the slight discrepancy made any difference. What I DID claim is that you can't equate energy with power. That's where the mistake was. And that DOES make a difference.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/2/2009 2:19 pm ET by Riversong
Yeah. I ain't beatin' up on you personally ... just commenting on the conversations.
Energy ... you mean energy consumption ... over time? Available energy (KW) is one thing ... how long you use it (consumption) is another. Loads are one thing, the use over time is another. That's what I've been trying to get some people to understand for a long time now. It's one thing to design a system (for peak load)(load analysis). It's another to analyze that building/load over real time under real conditions (consumption analysis). While definately related, it takes different knowledge/skill set for the two. Engineers ain't energy consumption experts and I ain't no systems engineer.
It's one thing to design a system (for peak load)(load analysis). It's another to analyze that building/load over real time under real conditions (consumption analysis).
What you call "consumption analysis" is completely irrelevant except to that particular consumer.
The only way to compare buildings or building systems is by steady-state peak or daily or annual load analysis.
Actual consumption is depenent on hundreds of occupant-determined and controlled variables and offers no useful measure of a building's efficency. It is only a measure of the occupant's lifestyle.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
No more than comparing my Toyota with say yours or others. We make adjustments for e.g. model, weight, and engine size, etc.
In the energy modeling/analysis world, we typically compare 'gas mileage' between similar building occupancies on a per sqft of floor area basis. Assuming generally that offices, hospitals, etc. are occupied similarly, you can begin to assess ... 'are we doing well?' or not. You can also determine performance of that specific building over time ... like tracking your cars gas mileage to discover a problem or verify an improvement.
So no ... it is NOT completely irrelevant. I've been doing this for almost 30 years successfully. While it certainly lacks precision, this field is not rocket science. If my residence consumes 120,000 Btu/sqft/yr ... I am reasonably confident that this is high. Maybe it is due to a life style that is unique (e.g. mad scientist lab in the basement), but if it is a 'typical' occupancy, I'd have to say there is much room for improvement.
This can get complex fast, but DOE and other agencies have gathered just such information to enable us analysts to make rough judgements about performance. As you say ... many many factors can affect performance of a specific building. Many buildings share very similar characteristics, though (e.g. offices and occupied times), so you can make comparisons with the other similar occupancy down the street.
"Available energy (KW) is one thing "KW is not a measure of energy. It is a measure of power, the rate at which work is being done.http://en.wikipedia.org/wiki/Power_(physics)
http://www.glenbrook.k12.il.us/gbssci/phys/Class/energy/energtoc.html
.
William the Geezer, the sequel to Billy the Kid - Shoe
That is why I said 'available' maybe that isn't quite the right term ... kind of like potential energy vs. kinetic energy. KW is a measure of energy that is either available or being used at any instant (e.g. the instant KW draw of an electric heater). KW is the draw at any instant ... taken over time, it accumulates electric consumption. We're talking about the same thing, I think.
I made a mistake that is akin to using the term volts when you really mean amps. I'm glad that Riversong caught that as, hopefully, I won't make that mistake again.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
It does take volts AND amps to make power (KW), so it's all good stuff.
r u crazy ?
it's your SIL..... u no..... one of the people who gets to help pick your nursing home
back off, jack
Good greif I hope not. Probably have me stuck in a fish camp. <G>
Pulsing won't change the equations -- there are so many BTU per KWH of resistance heating. Except in a few parts of the country where electricity is cheap or gas expensive, gas will always be the better deal.
I tried to explain that to him but he is kind of hard headed, some times it take a 2x4 to get his attention. Simply put you are right, here we have to use gas to make electricity and it will always cost more, especially since our gas is running out.
Electricity is .099 per kwh, natural gas is .121 per therm.
If those are your current prices, then your electricity costs $2.87 a therm. But that gas price doesn't look right. Don't you know what you're paying? Check your bill.
If you already have hydronic heat, it's foolish to use anything else for a radiant floor.
But what do you mean by "built up floor over an uninsulated slab"?
It' also foolish to put radiant heat on an uninsulated slab. Is there significant insulation in that "built up floor" or just sleepers?
Make sure you have someone design and install the system properly or you're likely to regret it. The heat load and tubing spacing and flow rate and fluid temperature and temperature drop all have to be calculated, and then an appropriate tubing layout designed with proper manifold, mixing valve and circulator.
Solar & Super-Insulated Healthy Homes
Riversong you are 100% correct in the engineering department. Yeah I have a uninsulated slab 30 yr old house. Didn't know about insulating it in those days. IF I were to worry enough about heating it I would put down a couple inches of blue board and then sleeper in the pex and sheet over. I think the cost to benefit ratio is not there though.
BTW just got my home energy audit. Had to get that done so I can collect on some state money to upgrade the waterheater to a "side arm or boilermate" indirect fire tank" and replace the old fireplace with a more modern one with seal-able door.
The audit said my house is a 4 star 81.6 points so I have to do some sealing of the outlet boxes and pull all the window trim and seal around the windows, replace the garage door, find a electronic damper for the unit heater in the garage. Surprisingly enough the windows are not cost effective to replace but several are dead thermopanes which I will have to replace anyway.
I can get maybe 4K back if I spend 10-15k depending on my post audit. Not great but still a bargain. The state caps it at 10K but I would have to go to a 5 Star+ to qualify and it would cost 30-40K to get there and maybe more.
I wonder if he got this mixed up with off peak storage systems.
Those do "pulse" the electricity. But it might be 12 hours on and 12 hours off. In some places you can special rates during low system usages. I have heard of rates in the 1-2 cents/kWh range.
But you need to store the heat in a system some system where you can the release it under control.
Would not work for direct floor heat.
William the Geezer, the sequel to Billy the Kid - Shoe
Actually, would work for direct floor heat, sort of. Especially with no insulation, the thermal mass you're dealing with is fairly large.Another point: While electric isn't the most efficient or cost-effective choice in most cases, it does make sense for heating small areas, such as a bathroom floor, since it's much easier to manage than in-floor hydronic.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
I've installed a small elec radient heat floor in my small bathroom. IIRC, it uses 90 watts of energy and covers about 10 sq'. It has a timing hermostat that lights it up twice a day, once for morning dressing and once for evening cleanup.
The only thing it does is keep your toesies warm so you don't have to cover my purty tile job with a rug. It DOES NOT warm the bathroom to any appreciable degree.
Tu stultus es
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
Thanks guys for all the information. You collectively are a wealth of knowledge. I appreciate the time and trouble you put into the replies.
Jim
No trouble at all -- we enjoy so much arguing with each other.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
DO NOT!
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
Lag bolts suck!
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
The only thing it does is keep your toesies warm so you don't have to cover my purty tile job with a rug. It DOES NOT warm the bathroom to any appreciable degree.
That's the function of a radiant floor, and that's what makes them more efficient.
Thermal comfort is equally dependent on the mean radiant temperature of the surfaces of a room as it is on the air temperature (also upon relative humidity, convection velocity and turbulence, radiant asymmetry, temperature stratification, clothing value and metabolic rate).
In other words, with a warm floor the air temperature can be significantly lower for the same human comfort. And people prefer warm feet over warm heads.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
There is another contrast in this situation too to be considered. Paul's bath floor warmer in California is a wholly diffferent scenario that Taliskers whole house heat in Alaska.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
So did you catch the article in JLC (or FHB, I forget) about building myths? It was about radiant heat being more energy efficient than other heat types. The author pointed out that people with radiant heated floors tended to raise their thermostats, thus negating the energy savings. Had you heard that before?
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
The author pointed out that people with radiant heated floors tended to raise their thermostats, thus negating the energy savings. Had you heard that before?
Nope. But operator foolishness doesn't negate the physics of a radiant floor. The operative temperature of an indoor space is defined as the average of the air temperature and the mean radiant temperature of all surfaces. This is primarily what the human body experiences (in addition to convection) and how we judge our personal comfort.
So, with a warm floor (floors work better than walls or ceilings), a person will feel an equal level of comfort at lower air temperatures (as long as there aren't other cold surfaces, like non-lowE windows).
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I'm not doubting the physics of it, or how it should theoreticly behave.
The author was noting a study in Canada (not sure who did it) that measured the actual temps the end users of radient floors set them to. They were setting them higher than they should have been. I'm thinking people may actually be sensing and reacting the colder air, either through convection or their own movement through the house.
If you're big into radiant flooring, I just thought you should know about that - it might pop up out there.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
The author was noting a study in Canada (not sure who did it) that measured the actual temps the end users of radient floors set them to. They were setting them higher than they should have been.
From the Canadian Mortgage and Housing Corporation:
"A study by CMHC (Thermostat Settings in Houses with In-Floor Heating, #01-106) has shown that people tend to keep their thermostats set the same as if they had a forced air system. Even so, the warmest air is at the floor where it is desired (and not at the ceiling) and there is reduced heat loss through the ceiling and walls."
Again, this is user error based on habit. But the study suggested that even with normal thermostat settings, there should be less heat loss.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
There are two kinds of electric floor systems. One is only called a 'warmer' because it just warms the floor. It is not designed to be a space heater to make enough BTUs to heat the room space, only to take the chill off a tile floor.True radiant heat can make more heat, and can operate over a longer period without burning up.People need to pay attention to whether they are buying a floor warmer or a heater for the bathroom
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Good application/example! Hope you have your timer set to anticipate the occupancy by coming on say 1 hr early. Doesn't have to heat the space ... that is the beauty of radiant floors ... warm floors warm heart (er feet)! I've stood naked in a hot springs at -20 degF and been comfortable in spite of only my feet in hot water.
Ya, I could picture that... hey, nice birthmark!
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
It takes about 100 Btu of fuel to make about 40 Btu electrical energy. Converting electrical energy back to heat is one of the dumber things we do, out of convenience. I'm guilty since I have an electric oven.
If your son is right he has a bright future in science because he has proven wrong the 2nd law of thermodynamics.
True, btw that is my son in law. He is good to my daughter though.
One h e l l of a fisherman. He can limit out in the Russian river quicker than anybody I know. (Usually 3-6 Sockeye salmon depending on the opening, coho fly only).
About home/car repair he is out in left field most of the time. <G>
Cool. Fishing's more fun than thermodynamics anyway. No one wakes up at 3 am on a Saturday to do thermodynamics.
"Cool. Fishing's more fun than thermodynamics anyway. No one wakes up at 3 am on a Saturday to do thermodynamics."
Wanna bet?