Heat output, steam vs hot water

Pumpguy

We all know that a steam radiator filled with steam at 215* F. is steam at 1 PSI. And a hot water radiator would typically have, what, 180* F. water temperature?

And say that steam radiator at 1 PSI pressure had a heat output of 250 BTU. What would the heat output be for that same radiator with 180* F. water? 170* F. water?

Obviously, because of the lower temperature of the hot water, the heat output would be less than steam, but just how much less at typical hot water heating temperatures?

EBEBRATT-Ed

1 square foot of steam radiation is 240btu/hr. The same radiator on hot water is rated 185 btu/hr with water at 190 (average water temp) 200 in 180 out.

I think on the old gravity HW systems they used 150 btu/sq ft

Jamie Hall

There's a table for that somewhere... but for a rough estimate you can come startlingly close by subtracting 70 from the average water temperature and multiplying by 1.5.

EBEBRATT-Ed

I found it.
This is from my old copy of the "Burnham Heating Helper"

AVG water temp btu/sq ft

110 30
140 90
160 130
170 150
180 170
190 190
200 210

Ther's more temps in there but I didn't type them all.

If you search Burnham's site you can download the heating helper.

Seems to be some differences depending on what book you look in

Pumpguy

Thanks all,
I have a customer considering converting his 2 pipe steam system to hot water. Just wanted some numbers to show how this change would affect heating the home using the same radiators.

@EBEBRATT-Ed , your reply is consistent with information I got from another source.

drooplug

Are you trying to talk him out of converting? Converting to water should help quite a bit on his heating bill. Depending on heat loss and amount of EDR available, you could probably get the water temps much lower and heat the home just fine.

ChrisJ

drooplug said:

Are you trying to talk him out of converting? Converting to water should help quite a bit on his heating bill. Depending on heat loss and amount of EDR available, you could probably get the water temps much lower and heat the home just fine.

SeanBeans

@ChrisJ LOLOL

Jamie Hall

drooplug said:

Are you trying to talk him out of converting? Converting to water should help quite a bit on his heating bill. Depending on heat loss and amount of EDR available, you could probably get the water temps much lower and heat the home just fine.

What you say about heat loss and EDR is true so far as it goes. Unfortunately, it's not true that you can save on your heating bill by converting to hot water from steam. A BTU is a BTU, so if the system is properly controlled it will take the same amount of BTUs to heat with steam... or air... or hot water... or electricity... or whatever is handy.

The most the customer could possibly save would come if he could run the system cool enough all the time to take advantage of condensing technology. Then yes, the customer might be able to save as much as 7 to 8 percent.

But... would that be enough to pay back the cost of the conversion and additional maintenance? Probably not; one would have to do a rather sophisticated financial analysis to find out.

I have no hard objection to people advocating for hot water heat. There's a lot to be said for it. I do have an objection to advocating for conversions of this sort on monetary grounds, since -- not to put too fine a point on it -- the arguments in favour of the conversion are false, and do a disservice to the customer and the industry.

The Steam Whisperer

Yep, and they would now pay a bunch more in electrical than they used to to run the pumps and if a " high efficiency " boiler draft fans and all the electronics to go with it. And the possibility of freeze ups....which really reared it head this past winter here in Chicago.

Pumpguy

This homeowner has vacuum pumps that are original to the house, 1928, that are in need of overhaul or replacement. I could overhaul them, but he would still have old technology; leaking packing boxes, special air check valves, rust prone cast iron housings, and motors needing coupling alignment.

I have offered to fit modern conversion condensate and vacuum pumps to his receiver. These would have modern pumps with mechanical seals and 56J frame motors, along with new float and vacuum switches and electrical starters. Any future service would be straightforward pump repair, and not require the skill or product knowledge the existing pumps do.

Either alternative is an expensive proposition. I have been advising the customer for several years now that this day wold come, and it now is here.

Customer has always complained of house being cold, and he has asked about converting to hot water. Discounting the cost of conversion to hot water, it appears that the reduced heat output from hot water vs steam in his radiators would just contribute to that problem. Only solution then would be to add more radiators.

Jamie Hall

Pumpguy said:

This homeowner has vacuum pumps that are original to the house, 1928, that are in need of overhaul or replacement. I could overhaul them, but he would still have old technology; leaking packing boxes, special air check valves, rust prone cast iron housings, and motors needing coupling alignment.

I have offered to fit modern conversion condensate and vacuum pumps to his receiver. These would have modern pumps with mechanical seals and 56J frame motors, along with new float and vacuum switches and electrical starters. Any future service would be straightforward pump repair, and not require the skill or product knowledge the existing pumps do.

Either alternative is an expensive proposition. I have been advising the customer for several years now that this day wold come, and it now is here.

Customer has always complained of house being cold, and he has asked about converting to hot water. Discounting the cost of conversion to hot water, it appears that the reduced heat output from hot water vs steam in his radiators would just contribute to that problem. Only solution then would be to add more radiators.

How, exactly, is this piped? What I mean is... is the system piped essentially as a two pipe system with a vacuum assist to it, or is it one pipe steam with the vacuum being applied in place of vents, or ???

Reason I ask is have you considered ditching the vacuum assist entirely, and redoing the system as either a one pipe or two pipe more conventional system? I'd suggest giving that option some very careful consideration, although it will require some creative thinking on your part.

Can you describe the existing system in -- as one chap I knew would have said -- vast and terrible detail, and see what we can make of it?

jumper

The big negative for steam is that somebody is supposed to check boiler fairly often. I saw several multi-residential conversion projects that disappointed owners.

EBEBRATT-Ed

@Pumpguy
a heat loss of the building versus the heat output of the existing radiation if used on hot water would tell the story. Steam radiation was frequently oversized

The Steam Whisperer

I converted several former vacuum systems to orificed systems with or without steam outdoor reset with excellent success.

Pumpguy

@Jamie Hall, This is a 2 pipe vacuum return system. Unfortunately, the system was originally installed with low returns in the heated basement. These low returns flow into a floor level return line, and then into an auxiliary accumulator tank with float switch.

In addition to the usual air removal and pressure reduction functions of the vacuum pump, the vacuum is also needed to lift condensate from the auxiliary accumulator tank up into the main receiver.

See attached file for more details.

If this had been a common gravity return into the receiver tank, as an alternative, I would have offered just conversion condensate pumps to fit the existing receiver. These would have been offered with the provision that vacuum pumps might also be needed, and If needed, could be added later.

Converting to straight condensate pumps would have been a much lower cost alternative and an easier pill for the customer to swallow.

Steamhead

How about a mechanically pumped accumulator tank as the auxiliary, as described in chapter 12 of Lost Art? That would eliminate having to use vacuum to lift condensate.

Oh, and as far as alleged "savings" from converting steam to hot-water, these are bogus as @ChrisJ , @Jamie Hall and @The Steam Whisperer say. Fixing the steam will show similar savings without any of the many conversion pitfalls. Here is one of many threads covering this:

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

Jamie Hall

Seems to me that you could allow condensate -- and air -- to flow as it does now, to the accumulator tank...

dang. @Steamhead beat me to it.

Then use a regular boiler feed pump to get the water out of that tank and into the boiler -- but wire it as a boiler feed pump, not a condensate return pump!

Pumpguy

@Steamhead , @Jamie Hall, Not a bad idea, but here's just no room.

The aux tank is tucked into a trench just below floor level. The wall separating the pump room from other rooms in the basement straddles this trench, and the aux tank is right under this wall. The pump room is about the size of a walk in closet, and is in part responsible for the pumps not being serviced and maintained as they should. I can't do a proper job of getting to the back stuffing boxes on these pumps to replace the packing.

The existing vacuum pump package is way oversize. The house was originally 3 stories, now cut down to 2. I have seen similar sized vacuum pump packages in grade schools and apartment buildings. The only way to get that monster out of there would be to break it up with a sledge hammer and carry it out piece by piece.

Jamie Hall

Tine to get really creative. I take it the condensate can return to that silly tank OK, but the trick is going to be to get it to the boiler from there? Preferably without the vacuum pumps? Well... it can be done. Can you slip the suction pipe -- and foot valve -- from a jet pump in there? The output will be way more pressure than you need, but it will get the water to the boiler. To protect it from running dry and losing prime, is there a way to put a float valve in that tank, and control the water level in the tank with the float? Like a toilet tank... The jet pup would be operated by a low water sensor on the boiler... any makeup water would go into the tank...

Just an idea.

The Steam Whisperer

Cutting the concrete floor and putting in a small pit isn't that big of a deal . I had the same situation in a condo building a year ago. A little 18 inch lift right before the vacuum pump up from the tank. We cut the old vacuum/condensate unit free and installed a small pump in the pit of the old Kewanee that was just a few feet away. Had all the controls and motor mounted on the top to avoid problems with flooding in the pit.

luketheplumber

This might be a little off topic but why was the house cut from 3 floors to 2 floors?