energy use: forced-air vs hydronic

Voyager

I have seen mostly comments here about forced air that seem to not know about any of the advancements in forced air in the last 30 years. Unfortunately, I have seen precious few studies on the subject. I did see one a few months ago that compared a few system types all in the same exact structure, and forced air fared very well.

I have said it before and will say it again, and I realize this isn't really a heatinghelp forum, it is a hydronichelp forum, but a MODERN (not 60s or 70s) forced air system is a marvel of efficiency, flexibility (AC, ERV/HRV integration, humidity control, and even control of pressure inside a structure) and, yes, comfort. I live with such a system and it is very nice indeed. I also have a hydronic radiant system in a new workshop and it is also very nice indeed, but nice in different ways.

Voyager

ChrisJ said:

What really bothers me is how the world seems to create the impression that heatpumps are modern and efficient and yet steam is old and inefficient. Meanwhile............they are both basically the same thing as far as how energy is transferred.

As far as I recall, phase change is 100%, or very very close to 100% efficient, no?

Though we do pay to generate what ever amount of pressure is necessary to distribute the steam. That isn't free, in theory. Even if the system is in a vacuum you still need a pressure differential between the source and the condenser.



If an 850 watt blower is around 3000 btu/h, how much heat are most of the ECM blowers generating? It must be much lower, no?

I would not think there would be a significant difference in efficiency assuming equivalent boilers and such. I am not a steam expert, but from what I have read here it seems to me that steam is more costly to install needing large iron pipe rather than skinny copper pipe and probably not as easy to run the piping in a modern construction home. Maybe the extra cost of the hydronic circulators offsets that to some degree, but given that most circulators only cost about an hour’s worth of labor cost, even a 5 circulator system only costs about 5 hours of labor, so can a steam system be properly installed with a labor penalty of only 5 hours compared to a copper hydronic system?

Can a steam boiler effectively heat the floor the boiler is located on? Don’t you need some elevation between boiler and radiators? With many homes in many parts of the country not having basements anymore, will a steam boiler work effectively on a single level home?

Steamhead

Voyager said:

I would not think there would be a significant difference in efficiency assuming equivalent boilers and such. I am not a steam expert, but from what I have read here it seems to me that steam is more costly to install needing large iron pipe rather than skinny copper pipe and probably not as easy to run the piping in a modern construction home. Maybe the extra cost of the hydronic circulators offsets that to some degree, but given that most circulators only cost about an hour’s worth of labor cost, even a 5 circulator system only costs about 5 hours of labor, so can a steam system be properly installed with a labor penalty of only 5 hours compared to a copper hydronic system?

Have you taken a look at @gerry gill 's mini-tube systems, based on the Iron Fireman SelecTemp system from the 1950s?

Voyager said:

Can a steam boiler effectively heat the floor the boiler is located on? Don’t you need some elevation between boiler and radiators? With many homes in many parts of the country not having basements anymore, will a steam boiler work effectively on a single level home?

Sure it can. But you do need a return pump to receive the water and return it to the boiler. This is usually a boiler-feed pump. But it runs far less than a hydronic circulator.

Voyager

Steamhead said:

Sure it can. But you do need a return pump to receive the water and return it to the boiler. This is usually a boiler-feed pump. But it runs far less than a hydronic circulator.

In a single level home, what is the advantage of steam over hydronic? Why would a homeowner choose steam for a new installation?

Keith M

1. Please see attached. Some contractors still do shoddy work. Leaking water pipes are easily seen, not so with leaking air ducts. This answers the infiltration/ex-filtration and how warm air drys the air questions. The higher the infiltration/ex-filtration is, the dryer the inside air is. After all humidity level is "relative" to air temperature and cold humid air infiltrating a building becomes dry air when it heats up...cold dry air just becomes dryer...
2. You want air movement across your skin in the summer for cooling. We do not not want the cooling effect or air movement during the heating season.
3. baseboard heating is perimeter heat and heats where the heat loss is. In addition it catches cold drafts and warms them before they spread across the room.
4. It takes less energy to move heat by water than by air.
5. We want to satisfy our comfort level and not just the thermostat on the wall.
6. I have lived in houses heated with warm air and baseboard and know baseboard is much more comfortable.
7. While I work for a manufacturer of "wet heat" I sincerely believe wet heat is more comfortable than warm air heat.
8. Even big buildings, such as the Freedom Tower, have perimeter "wet heat".
Keith Muhlmeister
Slant/Fin Corporation

Steamhead

Voyager said:

In a single level home, what is the advantage of steam over hydronic? Why would a homeowner choose steam for a new installation?

1- You can use smaller heat transmitters with steam;

2- Steam systems typically heat up faster than hydronic, assuming they are properly vented;

3- In an extended power or fuel failure, there is much, much less danger of freezing damage.

4- If you use an orifice system, there are fewer moving parts with steam.

Plus, what @Keith M said.

Keith M

Steam heat is very nice heat. Just make sure you have a good knowledgeable installing contractor. I currently have steam and it is very comfortable.

Tinman

Smaller heat transmitters for steam is an awesome idea but 99% of the systems have about 40% more EDR than what’s needed.

The number of contractors willing to do a load calc first, then size (remove/reduce) the EDR accordingly are few and far between.

Voyager

Keith M said:

1. Please see attached. Some contractors still do shoddy work. Leaking water pipes are easily seen, not so with leaking air ducts. This answers the infiltration/ex-filtration and how warm air drys the air questions. The higher the infiltration/ex-filtration is, the dryer the inside air is. After all humidity level is "relative" to air temperature and cold humid air infiltrating a building becomes dry air when it heats up...cold dry air just becomes dryer...
2. You want air movement across your skin in the summer for cooling. We do not not want the cooling effect or air movement during the heating season.
3. baseboard heating is perimeter heat and heats where the heat loss is. In addition it catches cold drafts and warms them before they spread across the room.
4. It takes less energy to move heat by water than by air.
5. We want to satisfy our comfort level and not just the thermostat on the wall.
6. I have lived in houses heated with warm air and baseboard and know baseboard is much more comfortable.
7. While I work for a manufacturer of "wet heat" I sincerely believe wet heat is more comfortable than warm air heat.
8. Even big buildings, such as the Freedom Tower, have perimeter "wet heat".
Keith Muhlmeister
Slant/Fin Corporation

I’ve never had a leaky duct rot out wood in a structure or cause major damage.

I live in a home heated and cooled with forced air. The church I attend and do a lot of the maintenance work on has HWBB with minisplits for AC. I built a decent size workshop two years ago and it is in-slab hydronic.

The church is the least comfortable of the three. The HWBB is slow to heat up and since the church is used only two days a week, we simply have to set back in between to manage energy costs. And the minisplits are very drafty for AC. This is the least comfortable building I spend time in, either winter or summer.

My workshop is probably the most comfortable in the dead of winter when it is always pretty cold and the outside temps are only fluctuating 20 degrees or so day to night. In the spring and fall when the temps often cycle 30+ degrees day and night it is often too warm as the temp will overshoot 4+ degrees quite often. I have ODR and run fairly cool feed water, typically 80 degrees or so. You simply can’t take heat out of a 5” concrete slab when the sun comes out on a spring day and the temp goes from 10 F to 50F in a matter of a few hours. It is obviously the least comfortable in the summer lacking AC.

My house is the second most comfortable in the dead of winter and would be tied for most comfortable were the kitchen and dining room not above an unheated garage. The colder floors make those rooms less comfortable than the heated floor in the workshop. However, the heat and AC both respond quickly and without drafts. My system was designed by a very well respected commercial HVAC company and has tons of registers, many returns, is well balanced and has very low air flow velocity from the registers. You can’t tell when it comes on and goes off unless the house is completely quiet. It handles 8 degree setbacks at night easily and I wake up before the alarm in the morning when the programmable stat starts warming things up 20 minutes before alarm time. And my house is well sealed and has two HRVs and the air is no drier than in our church and about the same also as my workshop, which is probably leakier with the large overhead door.

If I were to build another house, I would use forced air as the primary heating and cooling system, HRVs again to manage indoor air quality, but I would supplement the heat with underfloor hydronic to give warm floors. That would give the ultimate in year-round occupant comfort, but at a price premium compared to any other system type alone.

Steamhead

Voyager said:

The church I attend and do a lot of the maintenance work on has HWBB with minisplits for AC. .......... The church is the least comfortable of the three. The HWBB is slow to heat up and since the church is used only two days a week, we simply have to set back in between to manage energy costs.

Then there's something wrong with it. Fortunately, you're in the right place to find someone who can help.

Keith M

A floor warming system with supplement heat is very nice and you can avoid the overheating that can happen with straight floor heating.
Sounds like your church was not designed properly or not installed properly or not maintained properly and perhaps all of the above. You can design for fast pick up for a sanctuary or any other area with any type heating system.
Does the church use outdoor temperature reset? That could also be the issue.
It may be a simple fix.

Tinman

Floor warming vs radiant heating. Properly designed, heat the space entirely with radiant heat. Unless you’re heating something like a sunroom, it can easily be done.

Voyager

I am not sure it was designed or installed that poorly. I think it is simple physics. The church has uninsulated wood floors over an unheated crawl space and 14 or 16’ high ceilings. That is not a good scenario for any convective heating solution. And if we run the ceiling fans very fast people complain about the drafts. This building is crying for radiant heated floors, but, alas, the cost...

Jamie Hall

Perhaps there is a useful bottom line here...

First off, a BTU is a BTU. Given a specific space, under specific exterior conditions, it will take exactly the same number of delivered BTUs to heat that space to a specific interior temperature, regardless of how you deliver them.

For fuel burning heating systems, the lower the returning medium temperature you can achieve, the higher the potential efficiency will be, assuming that the appliance is designed to make use of condensing the water vapour in the exhaust stream. Most steam systems cannot condense (a few can).

However.

Note the comment "delivered" there in the second paragraph. This is the second part of the equation: the system must be both designed and installed with best practices to achieve anything like good results. It doesn't matter what your heating medium is. High quality design and installation -- good results. Poor quality design and installation -- misery. We've all seen it.

Then there is comfort. Hitting a given space temperature is not the only criterion; draughts, for instance, when heating are to be avoided. This is particularly a problem with forced air, although careful attention in the design can often reduce the problem.

Then there is usage. If a space needs to have different temperatures -- for whatever reason -- over a day or even a week, most radiant systems have real difficulties and faster responding systems may be a better choice.

Oh yeah... I mentioned bottom line. Which is that a true heating professional will not be wedded to one and only one type of heating system. He or she will evaluate the problem and choose the system which best meets the desires of the client.

The Steam Whisperer

I almost always agree with nearly everything you post, Jamie, but a btu is not a btu. A btu in a radiant floor system is worth a lot more than a btu in a forced air system because radiant floor systems tend to cause reversed stratification..... cooler temps at ceiling and warmer temps at the floor. Cooler temps at the ceiling reduce direct conductive heat loss and reduce air leakage due to the stack effect of heated air. Therefore the amount of heat needed to keep a typical human comfortable in a space ( particularly tall spaces) is lower with the radiant floor system than with forced air. Radiant systems, no matter what type, almost always have this advancement over air systems.
Proper application of systems is really important. We have a client that was convinced to install heat pumps in a large church sanctuary. As I was reading the documentation on the units, I discovered the minimum indoor temperature was 58F. Now the building that had a system that could maintain the building at 45 degrees 6 3/4 days per week and then rapidly increase the temperature to 70F for services now has to be heated to about 60F 6 days a week and very slowly raises the temperature to 70F. Energy usage has gone up substantially due to the misapplication of a heat pump system.

The quantum leap in improvement of modern forced air furnaces is no doubt huge. Near continuous low pressure circulation with much lower, but steady supply air temperatures I can easily imagine have greatly reduced the problems of stratification and increased air leakage, but the problems are still inherent to the system.

Steamhead

Voyager said:

I am not sure it was designed or installed that poorly. I think it is simple physics. The church has uninsulated wood floors over an unheated crawl space and 14 or 16’ high ceilings. That is not a good scenario for any convective heating solution. And if we run the ceiling fans very fast people complain about the drafts. This building is crying for radiant heated floors, but, alas, the cost...

Insulate the floors and see how much better it does.

ChrisJ

Steamhead said:

Voyager said:

I am not sure it was designed or installed that poorly. I think it is simple physics. The church has uninsulated wood floors over an unheated crawl space and 14 or 16’ high ceilings. That is not a good scenario for any convective heating solution. And if we run the ceiling fans very fast people complain about the drafts. This building is crying for radiant heated floors, but, alas, the cost...

Insulate the floors and see how much better it does.

I think what you actually meant was, rip the steam out, insulate the floors, walls etc, install a modcon and then brag about the huge savings in fuel.

Obviously that doesn't apply in this specific case, but it seems to be what often happens.

In the end........it doesn't matter what system a building has if the building is broken.

hot_rod

what about the loss up the flue a mod con running 120 set compared to a steam or high temperature hydronic, the efficiency of the heat source needs to be factored in operating cost
Comfort should also be high on the list add or remove humidity filter stale or pollen air, orders etc

ChrisJ

hot_rod said:

what about the loss up the flue a mod con running 120 set compared to a steam or high temperature hydronic, the efficiency of the heat source needs to be factored in operating cost

Comfort should also be high on the list add or remove humidity filter stale or pollen air, orders etc

I'm not sure if you missed my point.

You can't completely change a building and rip out a broken steam system, install some other system that works properly and then claim it's all because it was changed from steam.

A heating and cooling system is part of the building. Really, the building is part of the "system".

If you have a very well insulated and sealed building with an 80% boiler or furnace, it will always do better than an equal sized drafty poorly insulated building with the most efficient system you can find. It will also always be more comfortable.

clammy

I ve been watching this thread and the aurgement between the to side of the coin .my view is take a look at European countries most are heating w hydronics and there isn’t much ac espically residentally plus who owned a home or townhouse ,it would seem to me under there energy conservations and costs of fuel gas / electric are higher then ours and space required for a air based system just gets thrown away . Those can talk of hot air virtues but duct work takes spaces and everyone wants every inch of space and flat full basement ceilings or it-gets hidden in a attic in un conditioned space and then wrapped w nothing better then glorified packing material you have to be a magician to make everyone happy and hope that it works 1/2 way decent.You can talk zoning air based systems till your red in the face let’s see u do a room by room like panel rads and trv,s I know minisplits ,but the price would not warrant it . And as for just electric costs there’s absolutely no way a compressor/ fan based heating system will ever use less energy then a hydronic system what a couple of pumps,and please don’t forget transmission costs .water based systems I feel are a little more forgiving when it comes to being butched up .i feel that probably later then sooner we will see more water based heating / coiling systems that will be indirect systems instead of direct using catalyst designed absorbing and rejecting agents that will store and continue to supply either heat or cooling .in closing there s a reason why mini splits and large vrf systems have a dis advantage is when installed in commercial spaces u need a ventilation system to evacuate in case of leakage ,that’s one large reason water or glycol based will never totally disappear .the other side is cost it’s much cheaper to wam bam a air based system the water and steam huge difference when the later leaks some one bound to see it air forget bout it
sorry for the rant just my thoughts peace and good luck

The Steam Whisperer

Chris J seems to have hit the nail on the head. Heating systems almost always get talked about as though they are completely isolated from the building. This simply isn't true... they interact with the building and how it is used. The example of the church I gave above is a case in point. The steam system was a much more efficient choice for the operating model of the building than the heat pumps. Leaky buildings ( which is just about everything built new or existing in the US) should be heated with systems that do not multiply this leakage. The performance of tight buildings, even if lightly insulated, is not impacted nearly as much by the type of system installed. For tight, very well insulated buildings, the extra investment of radiant floor is probably not worth while. The Mean Radiant Temperature of the spaces will naturally be higher than other buildings and the drafts and increased air leakage caused by a forced air system much lower. This can make for above average comfort.

The thermal efficiency of the equipment is important, but the thermal performance of the building itself is much more important. With the thermal efficiencies of steam or standard hot water running in the low to mid 80s ( we see 86 to 87% with steam on older,larger steel boilers) and mod cons running only about 5 to 10 points higher, the impact is much less. With hot water comes increased electrical use and what appears to be some small false increases in thermal efficiency and with forced air large increases in electrical use and what appear to be significant increases of false thermal efficiency (the heat of the electrical use is included in the units output), The overall efficiency of steam as a source of probably within about 5 to 7% of an equivalent condensing hot water system in an equivalent structure. Cutting the heat loss of most single family homes by 15 to 20% is pretty easy. If renovating, cutting the heat loss in nearly half is very attainable. In larger low rise structures cutting the heat loss by a 1/3 is often quite easy and very cost effective.

If we are truly going to pursue efficiency, we need to stop looking at the efficiency number of a component and begin looking at the complete building system and how the building is used. The dismal failure of so many LEED certified buildings has shown the problem of only looking at components and not the complete system.

Tinman

ChrisJ said:

hot_rod said:

what about the loss up the flue a mod con running 120 set compared to a steam or high temperature hydronic, the efficiency of the heat source needs to be factored in operating cost

Comfort should also be high on the list add or remove humidity filter stale or pollen air, orders etc

I'm not sure if you missed my point.

You can't completely change a building and rip out a broken steam system, install some other system that works properly and then claim it's all because it was changed from steam.

A heating and cooling system is part of the building. Really, the building is part of the "system".

If you have a very well insulated and sealed building with an 80% boiler or furnace, it will always do better than an equal sized drafty poorly insulated building with the most efficient system you can find. It will also always be more comfortable.

I love steam heat. I do. I love everything about it except for wet returns.

But, what if you do rip out a broken steam system and replace it with a different system, without making a single change to the building, and see significant improvement in gas useage?

On the only two steam systems I've replaced with another, I've seen those improvements. It can be done, but you really have to do your homework first to make sure you're going to see the intended results.

Jamie Hall

All of the above comments are quite true! Just varying points of view. As I said earlier, the heating professional has to take into account the building, the setting, the desired temperature(s) and the impact on the comfort for the occupants -- these all factor in.

Voyager

Jamie Hall said:

All of the above comments are quite true! Just varying points of view. As I said earlier, the heating professional has to take into account the building, the setting, the desired temperature(s) and the impact on the comfort for the occupants -- these all factor in.

100% agree. Unfortunately, I think this rarely happens. Folks with mainly hydronic baseboard will sell that. Folks with hydronic radiant will sell that. Folks with forced air will sell that. I see very few HVAC companies that understand and sell all system types and truly try to match the system type to the needs of the particular building and customer. I was lucky to have such a company when I built my house. I had planned for underfloor radiant as I had forced air in my last house and it was a 1960s system and was terrible. It was noisy, had wide temperature swings, moved lots of dust around, dried the air (it too its combustion supply from within the house), etc.

However, when the company’s engineer met with me to discuss what all I wanted (heat setbacks at night, AC, fresh air for good indoor air quality, possible humidification, etc.) he said that a forced air system was the best overall solution. When I gave my reasons for not wanting forced air, he educated me on the difference between a 1960s system and a 1990s system and convinced me that my fears were based on an old and poorly installed system and not on a modern and well installed system.

I finally agreed and have not regretted it. A modern forced air system is not remotely similar to what you find in spec homes and mobile homes. As for the central humidifier, we ended up not needing it. We found that running one humidifier in our living room is adequate given that our furnace and water heater heater use outside air for combustion, our house is fairly well sealed so most of the air “infiltration” is controlled by the HRVs. However, I still haven’t given up on adding a central humidifier at the time my furnace needs to be replaced and the ducts are more easily modified.

Even though I really like the forced air system in my house, when I built my workshop, I honestly assessed the building and how I would use it, and in slab hydronic was the best choice. However, in slab or underfloor hydronic is not the best choice all of the time, nor is forced air or any other technology.

Steamhead

Voyager said:

Folks with forced air will sell that.

Yup.

Voyager

Steamhead said:

Voyager said:

Folks with forced air will sell that.

Yup.

“Folks with mainly hydronic baseboard will sell that. Folks with hydronic radiant will sell that. ”

Yup.

Tinman

And some folks offer what's best for the customer without an agenda.

Solid_Fuel_Man

@Voyager its interesting as I'd put forced air in a shop or outbuilding. Fast recovery and no issues with freezing water if I decided not to heat it for a time. An attached shop frequently used may get radiant with unite heaters for fast recovery or a woodstove for burning woodworking scrap.

Solid_Fuel_Man

Ok if we are going to talk electrical consumption of steam.... a millivolt atmospheric one pipe will have zero electric consumption, but large gas consumption.

A power burner wet base boiler will have "much higher" electrical consumption but lower (maybe 10-15%) gas consumption.

An oil steam boiler will have similar electrical consumption.

A typical low river large commercial building will have several condensate pumps and/or trenches with wet returns which will be rotted put and cost money to replace and higher electrical consumption.

An atmospheric millivolt water system will have electrical consumption of at least one circulator (average 007 and a switching relay).

A mod/con in a large radiant commercial building with an ECM pump may draw a total of 500watts. But the boiler will need to be replaced and/or a circuit board or two. But will use the least amount of gas.

So, let's not use the word "dramatically" when you say steam has better distribution efficiency.

@ChrisJ you are speaking of phase change, well if we use phase change in the exhaust of an appliance to remove the latent heat (forced air or hot water) then the BTU input and BTU output are much closer than if we simply raise the temperature in the boiler to make the heat transfer medium (water) changing state, and condense in the emitters. All of that is 100% efficient technically, it's how much of the useful heat is actually delivered to the occupants that's useful.

Electric resistance heat is 100% efficient but no one wants to pay for that! We need to look at total energy (fuel and electric) into the heating system, and total comfort delivered for that heating dollar.

There is no correct answer!

All 3 have their advantages and disadvantages, air, water, and steam. And we are ALL just a bit bias aren't we?

Voyager

Solid_Fuel_Man said:

@Voyager its interesting as I'd put forced air in a shop or outbuilding. Fast recovery and no issues with freezing water if I decided not to heat it for a time. An attached shop frequently used may get radiant with unite heaters for fast recovery or a woodstove for burning woodworking scrap.

It depends on how you plan to use it. If it was a cold shop that was only heated when used/occupied, I agree with you. Mine is a warm shop as I keep several vehicles there on battery tenders and I prefer to keep the temp around 55 in case a tender fails to avoid battery freeze-up. I also store paint and other liquids that need to be kept above freezing. And when working, I prefer temps no more than 60.

So, I keep the slab at 55 most of the winter or at 60 when I plan to work for several consecutive days in the shop. It has worked pretty well so far other than in the fall and spring when the temp swings are large. When I start building my airplane, I will likely be in the shop daily and may need AC in the summer. I may then add an AC unit and also include some heat (heat pump most likely) which I can then use to bump the heat quickly from 55 to 60 while the radiant catches up gradually. Still debating if that is worth the investment, but I imagine driving a few hundred rivets on a 95 degree day may drive me to AC.

And as everyone agrees, nothing beats walking on a warm floor compared to a cold one, particularly when the cold floor is bare concrete or some other thermally dense materially.

The Steam Whisperer

The electrical usage for pumping condensate is minimal and is not required in most systems unless they are quite large. The typical hot water system has to move 48 times more water than a steam system to move the same Btu's .
Example:
10 gallons of water boiled into steam during one hour releases about 80,000 btu/ hr of heat. Pumping capacity needed for steam: 10 Gallons per hour. For a typical American design (20F delta t) system, delivering 80,000 btu/hr, this requires moving 8 gallons per minute. Pumping capacity needed for hot water: 480 gallons per hour. Hot water system needs to move 48 times more water.
If the system is a typical newer radiant floor system, the design temperature drop is only 10F, so the pumping requirement increase to 960 gallons per hour or 96 times that needed for steam.
If the system is designed to modern more efficient design (which still appear to be very rare), the delta tee would be about 40F, so the flow rate would be cut in half to 240 gallons per hour or still 24 times that needed for steam.
If running full outdoor reset like on most Mod cons, these flow rates will be required nearly continuously throughout the heating season, which is another place where the inefficiency of Modcons is ignored.
If supplied with a conventional on/off heat source, it is probably safe to say that these pumps will only run about 1/2 the time at most, probably less in older high mass systems. The on/off sources will have roughly double or higher distribution efficiencies than full reset Modcons.

As to the thermal efficiency differences between the same boiler model used for steam and for hot water, the Peerless 63/64 series boiler have been tested for both. The efficiency difference is about 1%, only a very small difference in efficiency. In large commercial boilers, we regularly see efficiencies of 85% or higher for steam boilers, but these require power burners. With Mod cons, I would expect the power consumption requirement to be similiar to modulating power burner steam units, so the difference in thermal efficiency is only about 5% to 7%. If adding a condensing economizer to a large power burner steam boiler, this boosts the efficiency another 3% or so if just using return condensate flow through the economizer. The boost in efficiency is limited because the condensate flow is so low. Of course adding domestic water heating to the economizer in large applications would probably give the steam boiler the same thermal efficiency as a mod con.
Small application Modcons will have higher thermal efficiency than small steam boilers ( about 10 to 12 points). However, most small gas steam boilers have almost no electrical usage, but Modcons will require dramatically more power to operate usually 2 circulators, a draft fan and a host of electronics. If adding up the fuel cost and electrical cost of both systems, it is likely going to give you a similiar overall energy usage cost.

Tinman

If you cascade two modcons with 10:1 turndowns like I often did, now you have a 20:1 turndown. 😎

Tinman

85% on commercial steam boilers? Smith 19s and 28s aren't at 85 and the only Weil 88 that's even close are the two very smallest, which are rarely used.

Tinman

And all of those gallons of water you reference in radiant heating doesn't add up to squat when you're using a very low, fractional hp ECM pump.

This discussion can be slanted every which way based on bias, hyperbole, and the facts that one chooses to share and not share.

The Steam Whisperer

We work with lots of steel boilers. When tuning the older Pacifics especially, and the Kewanees too, we can often get the stack temps well below 300F without even using turbolators and running 9 to 9.5% Co2. Cast iron boilers usually can't match the efficiencies of steel boilers, unless running at lower firing rates with mod burners.
The Primary steam heating boilers at the Art Institute of Chicago run in the low to mid 90s with thier condensing economizers.....I suspect they are running domestic water through them.

It takes power to move water, it doesn't care whether its in a steam system or a hot water system. I don't see where you think there is bias in those numbers, those are based on standard design calculations that we all use. The differences are staggering, but real.
If the power used for a radiant floor system adds up to squat, then think how much less power is used to move about 1/100 the amount of water..... if pumps are even needed at all.

Sit down and do the math.... I have had my eyes opened many times when digging up all the formulas and running the numbers. John S's article cited previously directly addressed the power issue of pumping in hydronics and the huge differences between systems.

Tinman

> @The Steam Whisperer said:
> In large commercial boilers, we regularly see efficiencies of 85% or higher for steam boilers, but these require power burners.

So you’re saying you’re getting 85% on Pacific and Kewanee brickset boilers? What’s your excess air?

The Steam Whisperer

Well we're running 9.0 to 9.5% CO2 so that corresponds to about
25% excess air. They often need some new seals at the doors, but we've had many that close up nice and tight so the only air getting into the boiler is that provided by the burner, as it should be. Most of the Kewanees are Type C design (above) or similiar. The only Pacifics I've seen are with the typical "noodle" riser connections. Most are dry base, but have bumped into some wetbase.
The other thing we have found with these boilers is something mentioned in the Kewanee original sales literature.... they are designed with very large radiant transfer areas. My head tech had one small Pacific with a well tuned and good condition power flame gas burner and changed it to a Modulating radiant output burner of the same capacity and saw about a 40% drop in fuel use. I am sure the modulation had something to do with that, but something else is going on there which I haven't been able to put a finger on. The Viessman engineers seem to have figured this out since they use radiant burners on thier boilers and seem to beat all the equivalent efficiency boilers with about 15% less fuel use.
I think the current engineering of heat exchangers is mostly focused on heat extraction from the flue gases and basically ignors the radiant transfer that could be possible. I have a feeling from our experience is that a huge amount of efficiency is being left on the table.

BTW: That Burnham above appears to be throwing a lot of water out into the system based on reports from the building. I just finished the iso for a proper header for it.
It's 4,700,000 input supplying about 430 radiators, about 170 traps, and using a safety factor of 3 only a 3/4 HP condensate pump is used. The building is big enough that it has its own street in Evanston. The boiler feed rate is only 8 GPM @ 10ft of head. A little 40 watt ecm pump could probably keep up.