Which is more economical

Henry

I design all sorts of heating systems and processes in food brewing and distillery. What do I have at home? 96% modulating fan and burner hot air system with a 2 stage AC. I have a gas fireplace certified as a heating appliance that has constant pilot. That cost me about $10/month. I have a HTP modulating condensing hot water tank. I have a gas stove and a natural gas BBQ. The design temperature here is -25F. I just got my gas bill for my 2000 sq/ft house. My consumption for the last 12 months was $1525.81 Canadian. At today's rate it is $1098 US. I have an electronic air filter that keeps the dog smell away as well as other odors. I could not heat a similar house for less using hot water or steam.

icy78

And........?

ChrisJ

Henry said:

I design all sorts of heating systems and processes in food brewing and distillery. What do I have at home? 96% modulating fan and burner hot air system with a 2 stage AC. I have a gas fireplace certified as a heating appliance that has constant pilot. That cost me about $10/month. I have a HTP modulating condensing hot water tank. I have a gas stove and a natural gas BBQ. The design temperature here is -25F. I just got my gas bill for my 2000 sq/ft house. My consumption for the last 12 months was $1525.81 Canadian. At today's rate it is $1098 US. I have an electronic air filter that keeps the dog smell away as well as other odors. I could not heat a similar house for less using hot water or steam.

Prove it.

mattmia2

Are you sure the pilot burner uses $10/month in gas. I mean your rate is different than mine, but that was about the cost of the gas my conventional gas water heater and range used in the summer the last time I looked which was a couple years ago.

JUGHNE

The number of CCF or therms are a better gauge of comparision.

Also how about KW usage for monthly usage in heating season compared to shoulder months of May/June and Sept/Oct?

Henry

81,001 cubic / Ft of gas

Henry

My lowest month was July while away for over 2 weeks. Therefore very little consumption 918 cu/ft. The fireplace is a Vermont Casting with dual thermopiles. The utility average for a heating appliance fireplace is about right at $10/month. My bill was $33.58 or $24.18 US.

Fred

A lot of missing data in your assumptions:
- What temp do you keep the house?
- Do you use setbacks?
- Hot water consumption drives gas usage too
- What upgrades did you make/spend money doing to the envelope?
- How much cooking do you do?
- Does it make sense to lump all of your gas appliances into what you are suggesting as "Heating the house"?
- What was the cost of that 96% efficient hot air system and what is the annual maintenance cost?
- What is the life of that appliance?
- You need to analyze the total cost of ownership to do a fair comparison. Gas is just one component.

Henry

I am heating air in the coldest weather at 130F. Hot water would be 160F (cast iron) and steam 212F plus. What takes more BTU?

Fred

Henry said:

I am heating air in the coldest weather at 130F. Hot water would be 160F (cast iron) and steam 212F plus. What takes more BTU?

Depends on how long each has to run and how much output each gives off, both during and after burner shutdown.

GroundUp

I don't think you understand how heating works.... A BTU is a BTU. Radiant systems can often run water down to 80 degrees. While that steam boiler may take more fuel to create 212 degree steam, the output to the house is the same as you're putting out with the furnace therefore running for a shorter period of time. You're missing a ton of data and simply spitballing numbers- what are the air temps at the ceiling now and what would they be with steam and radiators? Fact of the matter is you cannot definitively say which system would be more efficient

mattmia2

The heat emitters all take the same amount of heat, with the caveat that the forced air creates more pressure imbalances and increases infiltration so it takes somewhat more heat.

Hot water and forced air can have somewhat better efficiency transferring the heat to the water or air from the products of combustion than steam since the transfer rate is driven by the temperature differential.

Both hot water and forced air can be designed to condense the water vapor that is produced in combustion in to liquid water and recover ~5%-10% more heat from the combustion than most steam systems can. Many times cast iron radiation has enough capacity to run an outdoor reset curve and run at return water temperatures that support condensation in a mod con boiler for much of the heating season.

ChrisJ

Henry said:

I am heating air in the coldest weather at 130F. Hot water would be 160F (cast iron) and steam 212F plus. What takes more BTU?

hot_rod

Another thought, we all agree heat goes to cold, correct?

The rate of exchange is driven by the ∆ between the two.

Looking at the heat loss or transfer from a radiant system and a cast iron baseboard for example. I used these two emitters to best show extremes.

It would seem the loss through a typical 2X4 wall would be driven by that delta also.

Be interesting to look at both systems, or any combination of systems radiators, fin tube FA, with an IR camera.

Keeping as much heat energy in the conditioned space is the goal, any system that drives that delta, at the wall, floor or ceiling would seem to increase loss. It would seem the lowest emitter temperature would be the most efficient and less to operate.

Steamhead

ChrisJ said:

Henry said:

I design all sorts of heating systems and processes in food brewing and distillery. What do I have at home? 96% modulating fan and burner hot air system with a 2 stage AC. I have a gas fireplace certified as a heating appliance that has constant pilot. That cost me about $10/month. I have a HTP modulating condensing hot water tank. I have a gas stove and a natural gas BBQ. The design temperature here is -25F. I just got my gas bill for my 2000 sq/ft house. My consumption for the last 12 months was $1525.81 Canadian. At today's rate it is $1098 US. I have an electronic air filter that keeps the dog smell away as well as other odors. I could not heat a similar house for less using hot water or steam.

Prove it.

He tried once............

https://forum.heatinghelp.com/discussion/145002/actual-savings-over-steam-heating

hot_rod

a side by side comparison would be interesting. I suspect based on pure thermodynamics the system with 120 flue gas temperature would consume less fuel when compared to a 400° flue gas temperature. A combustion analyzer would also give crucial data.
For the sake of this discussion leaving out electric consumption.

Nothing against steam, I would propose the same question, prove a steam system uses less energy when compared to a low temperature mod con system, all things being equal.

Brewbeer

> @Henry said:
> I am heating air in the coldest weather at 130F. Hot water would be 160F (cast iron) and steam 212F plus. What takes more BTU?

On a design day, I’m heating water for my baseboard system to 130F. On a 40F day, 100 degree water is enough to keep the house at 70F.

Steamhead

hot_rod said:

For the sake of this discussion leaving out electric consumption.

That leaves out a critical part of the picture. By their nature, hot-water and forced-air need electricity to move the heat around. Gravity-return steam does not. Even the pump motors on pumped-return steam don't run all the time the burners are running, as opposed to the other two.

Henry

Bob, the math proves it, thank you. The higher the DT the more energy is used.

Steamhead

Not so fast, Henry. Your question was "Which is more economical". How long is that 96% modulating fan and burner hot air system going to last, as opposed to a cast-iron boiler?

You might get ten years out of the typical furnasty, and not much more from a mod-con. The shorter lifespan negates any slight fuel savings. Then, there's the aggravation your family suffers when the unit dies and the house has no heat. Might be grounds for divorce

My 1983-vintage cast-iron boiler could probably go another 35 years if I choose not to replace it.

When discussing what is "economical", you have to figure ALL the costs. That's why my next boiler will be cast-iron.

Jamie Hall

This discussion has a way of coming up from time to time -- and always dismays me slightly, as it tends to generate a good deal more heat than light. The only risk is that it can also generate mistaken regulation, which is genuinely harmful, but that is not a topic for the Wall.

Why does it dismay me? Simply because it does not take into account the overall system. For example. The house Cedric lives in use about twice as much energy, per square foot of usable space as the house Henry is talking about. It is heated by steam. Does this demonstrate that steam is less efficient that his hot air system? No. It does demonstrate that there are differences -- but without considering what the differences actually are one cannot ascribe the difference to possible efficiency differences between -- in this case -- steam and hot air. Without knowing more about the house Henry is using as an example, I would be foolish to speculate on the other possibilities, though I suspect that there may be some differences in overall energy loss rate in the structure; early nineteenth century houses with no insulation are not known for low heat loss values.

The more one concentrates on only one aspect of a complex system -- and heating a structure is a very complex system -- the less likely it is that one can come up with any useful information.

PerryHolzman

As a Mechanical Engineer... The boiler that recovers the most heat from the fuel is the most efficient boiler. Condensing ModCon wins on fuel conversion...

But; Steamhead is correct that is only 1 part of the efficiency puzzle

Electricity cost to run the boiler, controls, and fans or pumps also adds.

Unless you have a hand fueled old coal/wood boiler there is more"purchased" energy usage.

I think its likely that the burner/control energy usage will be similar for similar sized boilers between steam and hot water boilers (I expect oil burners to require more energy than gas as they have to pressurize the oil to about 100 psi, where the gas is supplied at adequate pressure and only an adequate combustion air fan is required).

Then we get into pumping cost of air or water vs natural circulation flow of a steam system (without a condensate pump).

The motors on furnace fans I have seen are much larger than I see on a hot water systems. Thus, I conclude that there is more energy cost in pumping air than hot water.

I believe the type of hot water system affects things. My house has a mono-T system with 1 1/4 piping & 1/2 pipe risers/downcomers to cast iron baseboard (Crane -1954).

That's a low pressure rise system that does not take much pump energy to circulate water on (Currently a Taco 007F5 pump).

So the question is the energy cost of a Taco 007F5 pump less, equal, or more than the cost of energy lost by not utilizing a non-condensing boiler with a much higher boiler exhaust temperature. That can be calculated; but, I don't have the time to delve into that at this time. I'd have to start with the pressure loss of the Mono-T system which would give me the actual energy use of the Taco pump from the pump curve; and then add other factors (I could also run an Amp-meter and likely find the same information).

I really question the hot water heat systems that use many multiple branches with small diameter tubing - with each branch requiring its own pump, and sometimes having a solenoid valve as well (which eats more electricity). Those are higher pressure drop systems with higher pumping losses. It would not surprise me in those cases if the Steam Boiler would be more efficient overall. I've never seen an estimation on the pumping losses for each of those circuits.

It would be a fascinating exercise for someone to calculate all of that out...

Have a great day,

hot_rod

Steamhead said:

hot_rod said:

For the sake of this discussion leaving out electric consumption.

That leaves out a critical part of the picture. By their nature, hot-water and forced-air need electricity to move the heat around. Gravity-return steam does not. Even the pump motors on pumped-return steam don't run all the time the burners are running, as opposed to the other two.

So pure thermodynamics cannot be discussed? Fuel to useable heat energy within the structure, period.

But even the electrical consumption discussion changes with ECM technology, 37W will circulate most, many hydronic systems. The inducer motors are also very low power consumption and only run full speed on design days. I suppose a WattMiser would indicate total electrical consumption, but I'm asking mainly fuel consumption for quanity of useable energy, certainly that is part of the bill.

mattmia2

The energy that goes in to the fan or pump doesn't evaporate, it also goes in to the structure(some of it goes to the basement, depending on construction more or less of that goes in to the living space vs out the basement walls and between the sill and foundation). It largely is a matter of cost of heat from electricity vs fossil fuel rather than is this energy used for circulation and control wasted.

pecmsg

Degree Days
Initial cost of equipment and life expectancy
Average fuel costs over the life of the equipment
Maintenance and service.

Jamie Hall

There are times when the temptation to throw in monkey wrenches overcomes me... may I respectfully point out that all of the energy going into pumps, head losses in pipes, boiler jacket insulation, etc. etc. etc. is useful for heating the structure, assuming that everything is inside the heated envelope? Even relatively high temperature flue gas may not be as evil as it seems!

Reminds me a little of the bad old days when the folks from Detroit advertised the horsepower of their cars' engines -- and then measured that power with none of the accessories on the engine (such details as water pumps, generators, cooling fans, air filters, exhaust systems... trivial bits and bobs of that sort) connected.

hot_rod

Jamie Hall said:

This discussion has a way of coming up from time to time -- and always dismays me slightly, as it tends to generate a good deal more heat than light. The only risk is that it can also generate mistaken regulation, which is genuinely harmful, but that is not a topic for the Wall.

Why does it dismay me? Simply because it does not take into account the overall system. For example. The house Cedric lives in use about twice as much energy, per square foot of usable space as the house Henry is talking about. It is heated by steam. Does this demonstrate that steam is less efficient that his hot air system? No. It does demonstrate that there are differences -- but without considering what the differences actually are one cannot ascribe the difference to possible efficiency differences between -- in this case -- steam and hot air. Without knowing more about the house Henry is using as an example, I would be foolish to speculate on the other possibilities, though I suspect that there may be some differences in overall energy loss rate in the structure; early nineteenth century houses with no insulation are not known for low heat loss values.

The more one concentrates on only one aspect of a complex system -- and heating a structure is a very complex system -- the less likely it is that one can come up with any useful information.

So on a hunch, if your building was retrofitted with a 120F design system it would be expected to cost more or less to operate, fossil and electrical energy cost.

hot_rod

Jamie Hall said:

There are times when the temptation to throw in monkey wrenches overcomes me... may I respectfully point out that all of the energy going into pumps, head losses in pipes, boiler jacket insulation, etc. etc. etc. is useful for heating the structure, assuming that everything is inside the heated envelope? Even relatively high temperature flue gas may not be as evil as it seems!

Reminds me a little of the bad old days when the folks from Detroit advertised the horsepower of their cars' engines -- and then measured that power with none of the accessories on the engine (such details as water pumps, generators, cooling fans, air filters, exhaust systems... trivial bits and bobs of that sort) connected.

Evil as an adjective for high flue gas temperature that's a new one.
What about simply wasteful?

Steamhead

There has never been a completely scientific comparison of heating a building by steam as opposed to hot-water, in the same building to eliminate that variable, and with both systems in optimum condition to eliminate that variable. Period.

The few "case studies" I've seen compared brand-new hot-water systems to steam systems that were in poor condition (most likely due to knuckleheading or lack of maintenance). Either that, or the steam systems' condition was not mentioned, as in the thread I linked to above (wonder why?). This is not a fair comparison, never was and never will be.

Over the years, I've kept asking for such a comparison and no one has been able to find one......................

Steamhead

hot_rod said:

Evil as an adjective for high flue gas temperature that's a new one.
What about simply wasteful?

But a chimney has no moving parts, whereas a mod-con needs an inducer fan, whose motor uses electricity and breaks down on a 5-degree night. Another repair bill, which detracts from its "economical" argument.

hot_rod

Steamhead said:

There has never been a completely scientific comparison of heating a building by steam as opposed to hot-water, in the same building to eliminate that variable, and with both systems in optimum condition to eliminate that variable. Period.

The few "case studies" I've seen compared brand-new hot-water systems to steam systems that were in poor condition (most likely due to knuckleheading or lack of maintenance). Either that, or the steam systems' condition was not mentioned, as in the thread I linked to above (wonder why?). This is not a fair comparison, never was and never will be.

Over the years, I've kept asking for such a comparison and no one has been able to find one......................

In the meantime you could run simulations, FEA analysis.

Use the formulas we have available to us already.

Define a load, run the calc for distribution efficiency which steam or gravity HW wins hands down. Fuel to heat energy conversion.

Then to be fair, installed cost for two new systems.

Keeping in mind from the past years here on the wall steam systems fail, boiler in some cases failing within 5 years, even properly installed ones. No boiler based system is install and forgotten for the next 20 years.

And to be fair all boiler/ mechanical system should have a yearly service performed, oil I imagine as critical as mod con to maintain efficiencies, and prevent expensive clean outs..

ChrisJ

@Henry my single pipe steam system is more economical than your furnace.

Here's zero actual numbers to back up my statement.

EBEBRATT-Ed

This is Fun! But I'm staying out!

Steamhead

Some more to chew on:

https://forum.heatinghelp.com/discussion/131555/new-steam-mini-tube-system-installed-in-my-own-house-iron-fireman-style/p1

@gerry gill , how's the fuel consumption on this masterpiece?

ChicagoCooperator

But what about comfort! Won't somebody think of the comfort!

(snark aside, comfort would also be an important component when comparing similarly economical system, right?)

hot_rod

I have never lived with a steam system, I have lived in several radiant homes, hard to beat that quiet, invisible, comfortable radiant surfaces heat.

Maybe comfort, like beauty is in the eye of the beholder

ChrisJ

hot_rod said:

I have never lived with a steam system, I have lived in several radiant homes, hard to beat that quiet, invisible, comfortable radiant surfaces heat.

Maybe comfort, like beauty is in the eye of the beholder

Have you ever lived with forced hot air?
You know......
Hot, cold, hot, cold, hot, cold, hot, cold.

Because there's zero mass, so when it's on you're hot and when it's off you're cold and there's really no way to solve it?


Let's actually assume just for the sake of argument Henry's claims are true. That his forced air system is slightly more efficient and cheaper to run than any hydronic system.

Assuming that here's my response.

mikeg2015

Not sure hte point.

I;m running around $2100 annually for a 3600sqft brick Victorian, 45 original windows not including transfoms with crappy 1970’s storm windows. Probably had 3x the glass your modern home has, 10’ ceilings, full basement, no wall insulation other than wall cavity, full attic with 13’ ceiling in the center with foil faced insulation in the attic.

Heated with 200k salvaged steam boiler from a house that burnt down 2 blocks away, with a new 40 gallon indirect. I have heat pumps, but electric rate jumped so high this last year I only use it for mild weather above 50-55F. Although the boiler is so small it doesn’t overshoot much anyway.

A hot water radiant system would probably save maybe $200. Forced air about $300, but I’d spend $200 more in electricity moving the air around.

hot_rod

The original question was a bit too vague. Many different efficiencies at play in a heating system.

Building efficiency, btu/hr heat loss
heat generator efficiency, conversion of fuel to useable btus
distribution efficiency pumping power, power to run the boiler itself
investment efficiency over 20 years expected repair and maintenance cost Certainly these cost could offset the % efficiency between an 80% and 92% boiler

The structure dictates how much energy is required to maintain a set temperature, regardless of the heating unit. the type of boiler/ system doesn't air cannot change that number.

The goal should be to supply that energy as efficiently as possible under the criteria I mentioned. Everyone gets to chose the heat generator, distribution emitter, fuel source, etc.

Passion dictates some of those decisions for many of us, obsession for others

ChrisJ

> @hot_rod said:
> The original question was a bit too vague. Many different efficiencies at play in a heating system.
>
> Building efficiency, btu/hr heat loss
> heat generator efficiency, conversion of fuel to useable btus
> distribution efficiency pumping power, power to run the boiler itself
> investment efficiency over 20 years expected repair and maintenance cost Certainly these cost could offset the % efficiency between an 80% and 92% boiler
>
> The structure dictates how much energy is required to maintain a set temperature, regardless of the heating unit. the type of boiler/ system doesn't air cannot change that number.
>
> The goal should be to supply that energy as efficiently as possible under the criteria I mentioned. Everyone gets to chose the heat generator, distribution emitter, fuel source, etc.
>
> Passion dictates some of those decisions for many of us, obsession for others

I think the original post was trolling.

hot_rod

Henry seems to have plenty of data that his conversion save his customers plenty of coin. Passion or obsession, you decide