Antique cast iron wall hung radiators BTUs

dbsmith

We had a 4 seasons sunroom added to our (*EDIT: 1938 brick Tudor style) home several years ago to replace a decaying screened in porch. We currently heat it (zone 5, Upstate NY) with a 40,000 (*EDIT 50,000) BTU Harmon 25 pellet stove. We were looking at Runtal vertical radiators, but a friend suggested adding cast iron radiators. I searched and found the radiators pictured below - cast iron, wall hung, each panel is approximately 13 x 27. We have a total of 9 individual panels, in the different configurations pictured. Our friend said each panel was 5,000 BTUs, so the 3 stacker was 15,000 BTUs with our (*EDIT 475K hot water) (***EDIT #3. THE LOCHINVAR IS 399,999 BTU'S.) Lochinvar Knight running at 180 degrees. I'm now doubting the 5,000 BTU calculation. I was hoping to travel this winter, but I fear we will be stuck here again, feeding the pellet stove.

EDIT: There were questions about the room. It is glass on 3 sides and the roof. The fourth wall is the brick outer wall of the house. We will mount the radiators on the brick wall. Dimensions are 22' (** EDIT #2 23') (one brick and one glass wall) by 13 ft ( **EDIT #2 12' 8 1/2")(both glass). The roof has a peak of 13' (** EDIT #2 12' 4 1/16") and the side walls are 8'(** EDIT #2 7' 8 3/8"). (** EDIT #2 The glass on the roof is Conservaglass+ with an R4.0 insulation value. The vertical glass is HPG2000 3/4"double pane glazing with an R 4.0 insulation value). It is constructed on 3' above grade slab (don't know how far below grade) on half and above the basement on the other half. We have hot water radiators throughout the house. (** EDIT #2 There is a window and a door from the living room to the conservatory that can be left open with fans to blow in heat from the house. We also have a ceiling fan in the conservatory to circulate heat)

We have also had wildly disparate calculations on the BTUs needed to heat the conservatory to 65 degrees. When we got the new Lochinvar, the plumber put a tiny baseboard in the room and said it would keep it above freezing. The Lochinvar rep had to come out and said it was not even remotely correct. When we contacted the manufacturer of the room, we were told to ask the plumbers. We asked 3 for quotes on heating systems and the range was 15,000 to 81,000 BTUs. Modine hot air units, heat pumps, vertical rads... So when our friend, who had been a salesman for a high end plumbing and heating store suggested antique cast iron, we trusted him. He found the gold set and said it would be sufficient. I found the other 2 by scouring the internet.

Steamhead

Do you have a steam or hot-water system?

EBEBRATT-Ed

Lochinvar Knight is hot water

jesmed1

You can make a rough estimate yourself of the heat output using the following table. Look at Table 3 for cast iron radiators, and find the BTU per sq ft at a given water temp. You say your Lochinvar Knight is running at 180 degrees, so a conservative guess at water temp in the radiators might be 160-170 degrees. That gives you a range of 130-150 BTU per sq ft of radiator surface. So to get 5,000 BTU/hr at 130 BTU/sq ft, you'd need 38 square feet of radiator surface. At 150 BTU/sq ft, you'd need 33 sq ft of radiator surface.

https://www.expressradiant.ca/pdfs/product_classic_sizing_how_to.pdf

Steamhead says below that the rated surface area for those panels is much lower than 33-38 sq ft, so it sounds like your doubts are well-founded.

Steamhead

The usual rating for these sections is 9 square feet EDR. Assuming 150 BTU per hour for each square foot, that's 1,350 BTU/hour for each section.

EdTheHeaterMan

You will get the best performance from those radiators if you mount them correctly on the wall. The top photo is correct orientation. The other two photos are incorrect. (I understand that are not actually mounted in those pictures).
The supply is on the bottom of this radiator where the valve is located. The return is out of the top of the radiator and water flow will exit there and return by gravity or a pump back to the boiler.

And by all industry standards you have a radiator that will have about 9 EDR per section so the 3 section one will offer you about 4050 BTUh when the water in the radiator is at 180°F and the room is at about 65°F.

if you can get all 9 sections in that room you will have an output of just a little over 12,000 BTUh. Hope this answers your query

Mr. Ed

EDIT
Radiators will work in either orientation. It is the opening locations that will limit you to what orientation you select. Unless, of course, you want to attempt to take them apart to reconfigure them.... GOOD LUCK WITH THAT!

EdTheHeaterMan

The 45,000 BTU pellet stove is probably a bit of overkill for that room. You need to do a heat loss calculation for that room to see if the 12,000 is adequate for that room. It might be. Can you give the dimensions of the room and how much of it is exposed to the outdoors, and the amount of glass on the outside walls

Is it 2 sides exposed to the outdoors or 3 sides? Is there an exit door to the outside?

Is there a roof over it or a heated room above it? Any insulation?

What is the floor like? Is it over a basement or on a concrete slab or open to the weather like the under side of a wood deck might be?

dbsmith

I have edited my original post to include more information on the room. It is a full insulated glass (oxymoron) conservatory attached to our brick house. https://www.fourseasonssunrooms.com/product-services/sunrooms/sun-and-stars-cathedral-rooms

Ahomeowner

I feel like heating this room is like heating the outdoors with all that glass, or a glass tent. There is basically no insulation except in the wall between the 4 season room and the main house (if there is any there at all considering the house was built in 1938.)  I see why it’s difficult to do a heat loss calculation. The person doing the calculation needs to enter the window sizes and orientations manually for the most accurate results and sometimes they don’t do that because it’s time consuming. Describing the walls and ceilings for the calculations is also complicated by the fact that they are not 2x4, masonry, or anything standard.  I’m guessing that the slab is uninsulated too, based on its previous use.  Have you considered using this as a 3 season room with a mini split heat pump and only using the pellet stove when you want to use the room in the winter? That would give you air conditioning too. I feel like this room would cost a fortune to heat continuously, which you would need to do if you have hydronic heat (or any plumbing) in there.  You could insulate between the basement and this room in order or isolate it from the rest of the house.  How is the 50,000 btu/h pellet stove keeping up on the coldest days? I guess that would give you an idea if the heat loss is close to 50,000 btu or not. A heat loss calculation on this room might be complicated and time consuming, so maybe not free. If the heat loss is lower, it can be heated with a mini-split all winter and turned off when you are traveling.

P.S. For comparison, my entire 2,100 sqft house in zone 5 has a heat loss of about 40,000 btu/h. Depending on what the true heat loss is, is it worth the cost to heat this room continuously?

jesmed1

Here's a very quick-and dirty heat loss calculation. Your heat loss is dominated by the glass (about 750 sq ft from 3 walls and cathedral ceiling) .

Then the question is what R-value to use for the windows, which you say are "fully" insulated. The sunroom mfr's website says their ConservaGlass NXT has R up to 7.7 for triple-glazed, so if you have the triple glazed, you could have an R-value close to that 7.7 number. Let's say 7. For a zero-degree outside design temperature and inside at 68 degrees, that's a heat loss through the glass of only 7,300 BTU/hr. That's quite low, even for insulated glass, but it's possible if you have the best-possible insulated glass.

If you only have double-paned insulated glass, then your best R-value is more like 4.0. That's the minimum recommended by your sunroom mfr, so it's likely your glass is at least R=4.0. Then it's about 13,000 BTU/hr lost through the glass.

If you just have average double-insulated glass with no film/coating, then the R-value is more like 2.0. The your heat loss through the glass is about 25,000 BTU/hr.

Since half the floor is over the basement, you can ignore that as a first approximation. The heat loss through the slab is complicated by the fact that the earth under it is generally warmer than the ambient air temp, plus not knowing whether the slab is insulated or not. Given those uncertainties, I'd say figure 5,000 BTU/hr loss through the slab.

So your heat loss on a zero-degree day could be anywhere the range of 12,000-30,000 BTU/hr, and that depends mainly on the R-value of the glass, which you should be able to obtain from the mfr, since you know how many thicknesses and what type of film/coatings you got on it.

And remember, heat loss calculations are based on 99% worst-case temperature in your area. So 99% percent of the time, you're not going to need that many BTU's. And since it's a just sun room, does it really matter if it's only 50 degrees in there when you're away on vacation? I assume there's no plumbing to freeze.

(As I said, this is a quick-and-dirty estimate that ignores other factors like air infiltration, solar gain, and other factors that are impossible for us to know at this distance.)

Ahomeowner

I just saw your edit. You have a 475,000 BTU/h boiler in a single family home?

dbsmith

Yes I do! It's 3500 square feet of living space, lots of radiators, and I participated in the NYSERDA program where they come and do an audit of your home and then a low cost loan for upgrades. The upgrade was the boiler and foam insulation on the basement sill and the attic. There is a separate zone for the conservatory. It is worth heating the conservatory in the winter because I keep some rare specimen plants in there. I also have 2 greenhouses, so heating costs are ridiculously high anyway.

dbsmith

I found the original plans for the conservatory. I have edited my post to include all the details including exact dimensions and the information on the glass.

jesmed1

So R=4.0 for the glass means you're losing about 13,000 BTU/hr through the glass at zero degrees. The dimension updates you posted don't change the calcs enough to worry about.

I re-read what you wrote about the slab and am not sure what you mean. You said the slab is 3' (feet?) above grade. Did you mean the slab is 3 *inches* above grade? That would make more sense. 

More important is whether the slab is insulated, and with what thickness/R value. Worst case, with no insulation you might be losing 7,000 BTU/hr through the slab, mostly around the perimeter. Loss through the half of the floor over the basement is probably negligible by comparison unless the basement is freezing cold.

So that gets you up to 20,000 BTU/hr. And it could be less if your slab perimeter is insulated. Most likely you're somewhere in the 15,000-20,000 BTU/hr range.

dbsmith

The slab is raised 2.5 feet above grade and covered with slate. It is likely dug down quite a bit. The half that is basement was for the oil tank and their root cellar. The lot was filled in the 30's, and the people who built the house had money, so the basement walls are thick - 4' in places. When they added the screened in porch in '48, they wanted only one step down from the living room, so the slab had to be tall. I doubt they would have insulated, I think the slab is solid. They liked cement, steel lathe and plaster. A lot.

If I am losing 20,000 BTUs per hour out of the window and the floor, how many BTUs do I need in order to maintain a temp of 65 when the average low in January is 12, but can go way below zero with wind chill (it hit 45 below with wind chill last year, and I had a perimeter freeze in the greenhouse). My husband thinks we figure the BTUs required for the space, which we calculated at 21,076 (using cubic feet of 2,990 (10 x13x23) and a temperature differential of 53 degrees (65 - 12)) and then adding the loss of 20,000 BTUs for a total of 41,076.

EdTheHeaterMan

I actually did a Load Calculation for heating that room. I did not do the Heat Gain because we are talking about heating only as you can see by the absence of Latent Heat numbers. It appears that with the Ceiling Glass and the wall glass along with a guess at the amount of door glass you might have, You will need about 27,000 BTU of radiation for that space. Since those 9 rads will only produce about 12,000 BTUh at 180° water temperature, you will need to go look for about 10 or 11 more panels. You could make the entire brick wall one big radiator. Or you might select to place 10 in the lower wall under the window like this.. I'm not sure how your room is designed with some lower wall or ALL CLASS from ceiling to floor.

The attached diagram and load calculation would change if you do not have 2 to 3 feet of wall below the windows like in the picture above.

The load calculation is based on very little infiltration because of how well everything is sealed up when they make those rooms. I watched a couple of videos to see what I might be dealing with. To get the R4 equivalent rating from my software the windows actually say triple glass. That is not a mistake. That is the closest thing in the drop down menu for the windows you have.

I usually charge a lot for this service but I did it just to see how it would turn out. That is a load of almost 100 BTUh per square foot. To put that into perspective, A 100 year old balloon construction home with no insulation might be near 50 BTUh /sq ft and new construction would be less than 20 BTUh /sq ft.

So you will need a separate zone for that room and a separate thermostat.

Good luck on acquiring more of those radiators. If it is done up just right, it could look great.

dbsmith

Thank you Ed. I am more than happy to pay for calculations that will help us. The room is actually glass from floor to ceiling on the walls and the entire ceiling as well. Basically a greenhouse attached to the house with the only non glass surface being the brick wall. The door to the outside is 30 x 80, glass again.
.

jesmed1

dbsmith said:

The slab is raised 2.5 feet above grade and covered with slate. It is likely dug down quite a bit.... I doubt they would have insulated, I think the slab is solid. They liked cement, steel lathe and plaster. A lot.

OK, wow. So a solid slab of concrete nearly 3 feet high, and the exterior of the slab is exposed to air, not insulated? That is going to lose a lot of heat. So it's worse than I estimated above. Ed's higher number is going to be closer to reality.

dbsmith said:

how many BTUs do I need in order to maintain a temp of 65 when the average low in January is 12, but can go way below zero with wind chill (it hit 45 below with wind chill last year, and I had a perimeter freeze in the greenhouse). My husband thinks we figure the BTUs required for the space, which we calculated at 21,076 (using cubic feet of 2,990 (10 x13x23) and a temperature differential of 53 degrees (65 - 12)) and then adding the loss of 20,000 BTUs for a total of 41,076.

Not sure where your numbers came from, but I think you're asking how to extrapolate a heat loss calculation to lower temperatures. Heat loss is directly proportional to the temperature differential. Ed can tell you what temperature differential he used to get his result of 27,000 BTU/hr above. From his screenshot, it looks like he used -10 outdoors and 70 indoors. That gives you a differential of 80 degrees. Now suppose you want to find the heat loss at minus 45 degrees. With an indoor temperature of 70, that gives you a new differential of 115 degrees.

Then to find the heat loss at minus 45 degrees, you divide the BTU's by the original differential and multiply by the new differential:

Heat loss @ minus 45 = 27,000/80 * 115 = 38,812 BTU/hr.

You asked about 65 degrees indoor instead of 70, so for that temp the BTU's will be slightly lower. I used 70 indoors for the above example to be consistent with Ed's calculations.

High winds makes it worse, as that will cool the room faster, but it's difficult to put a number on it.

jesmed1

EdTheHeaterMan said:

I actually did a Load Calculation for heating that room. I did not do the Heat Gain because we are talking about heating only as you can see by the absence of Latent Heat numbers. It appears that with the Ceiling Glass and the wall glass along with a guess at the amount of door glass you might have, You will need about 27,000 BTU of radiation for that space.

@EdTheHeaterMan Those numbers all look reasonable, but the OP said her ceiling glass was also R=4, and it looks like you used R=2 or so on the ceiling ("E Skylight", 320 sq ft). Changing it to R=4 will halve the BTU loss through the ceiling glass and drop your total to around 20,000 BTU/hr.

hot_rod

I think it will look more like a snowmelt design, as far as btu/ sq. ft

Any way to add some insulating window coverings for the evening hours. That could drop the load considerably for 1/2 the day

EdTheHeaterMan

@jesmed1

The actual R value of the skylight glass selected from the drop down menu is closer to R-3.5. The R value of the triple window glass is actually R-4.3, so that will balance out to some degree. I could spend the time to build an exact R-value component if I were going to do this for a living, but I was just doing this for my own knowledge. So I think that I'm pretty close at 27,000 to 28,000. I could be way off though because the first time I did the entire room with standard double glass with no energy saving features, the load actually came out to 49,000 BTUh. I then looked at some of the videos that the vendor had online, and tweaked the components and removed the infiltration to zero air changes per hour(ACH). There is probably at least 0.5 ACH so that will increase the heat loss some. So I'm conservative with 100 BTUh/Ft number. But that can be remedied with additional radiators if needed

Remember your previous Quote : "Right again as usual" from another Discussion!!! You need to remember that! LOL

Ahomeowner

EdTheHeaterMan said:

I actually did a Load Calculation for heating that room... That is a load of almost 100 BTUh per square foot. To put that into perspective, A 100 year old balloon construction home with no insulation might be near 50 BTUh /sq ft and new construction would be less than 20 BTUh /sq ft. So you will need a separate zone for that room and a separate thermostat. Good luck on acquiring more of those radiators. If it is done up just right, it could look great.

Ed,
What’s your opinion of the new 475,000 BTU/h boiler in the 3,500 sqft main house with new foam insulation on the basement rim joist and in the attic done at the same time as the boiler? The house was built in 1938 so presumably the walls are uninsulated and the windows are original. I wonder what the load calcs looked like when the boiler was selected? By your estimation of 50 BTUh/sq ft for an uninsulated ballon-framed house, a 175,000 BTU/h boiler would have done the job.

jesmed1

EdTheHeaterMan said:

@jesmed1

The actual R value of the skylight glass selected from the drop down menu is closer to R-3.5. The R value of the triple window glass is actually R-4.3, so that will balance out to some degree.

I see how you tried to balance things out. It's just that ceiling BTU's of 13,978 over 320 sq ft at an 80 degree delta T implies an R value of 1.8, not 3.5, so I'm just trying to understand the numbers. Anyway, heat loss from the slab might be worse too, so it's good to be conservative.

EdTheHeaterMan said:

@jesmed1
Remember your previous Quote : "Right again as usual" from another Discussion!!! You need to remember that! LOL

Will do.

dbsmith

Ed,
What’s your opinion of the new 475,000 BTU/h boiler in the 3,500 sqft main house with new foam insulation on the basement rim joist and in the attic done at the same time as the boiler? The house was built in 1938 so presumably the walls are uninsulated and the windows are original. I wonder what the load calcs looked like when the boiler was selected? By your estimation of 50 BTUh/sq ft for an uninsulated ballon-framed house, a 175,000 BTU/h boiler would have done the job.



Most of the windows were replaced with Pella Architectural series before the audit. I questioned the boiler size as we went from 450 to 475K when they told me it would go down. I was told it was due to the linear feet of the radiators and the lack of any meaningful insulation (it's rock wool). We can't put in new insulation because the outer walls are brick and the inner walls are plaster on steel lathe. There is a separate zone for the conservatory. Perhaps because the number of rooms? Conservatory, LR, library, DR, kitchen, office, powder room, 4 beds and 2 baths, and a 2 story hallway? We had the NYSERDA audit contractor, Security Supply and our plumber here going over the numbers because it was such a large boiler.

KC_Jones

dbsmith said:

Yes I do! It's 3500 square feet of living space, lots of radiators, and I participated in the NYSERDA program where they come and do an audit of your home and then a low cost loan for upgrades. The upgrade was the boiler and foam insulation on the basement sill and the attic. There is a separate zone for the conservatory. It is worth heating the conservatory in the winter because I keep some rare specimen plants in there. I also have 2 greenhouses, so heating costs are ridiculously high anyway.

Are you sure about that 475k? I don't see that boiler size in the Lochinvar literature, perhaps it's actually a commercial boiler?

If indeed that is the size and it is only to heat the 3500 sq ft house, then it is massive overkill and a rough estimation would put it about 3x the size you needed. And this was based on an efficiency energy audit? If so all of them should be fired because they are just plain clueless.

I know it's not the question you asked, but someone needs to give you a voice of reason. That was a royal screw up of epic proportions. I could have sized it better with all the worst rule of thumbs people use.

For a rough reference I have a 120+ year old house, balloon frame, limited wall insulation (rooms I've gutted), original single pane windows, the only upgrade I've done completely is attic insulation. And my house is barely scratching on 40 btu's per sq ft. Yours should honestly be better than that, but definitely no worse. That would put you at a boiler output needed of 140,000. I'd speculate an actual Manual J heat loss calculation would show less, but that's just a WAG based on your window comments.

How did the contractor arrive at that massive boiler size? No reasonable person doing this for a living should have thought that made sense, if they have ever actually done the math. Thankfully that boiler modulates down (hopefully they set up the outdoor reset for that) and is probably running on low most of the time...I hope.

hot_rod

Was the greenhouse load factored into that boiler size?

dbsmith

I am told yes, they did factor in the conservatory, but they can't tell me at what load. I asked for the original load calculations, but no one kept them. I just took a picture of the Lochinvar. It is a Knight XL commercial boiler. I can't find the model number on it. It is 399,999 BTUs. We went up from 350,000 B
TUs.

hot_rod

dbsmith said:

I am told yes, they did factor in the conservatory, but they can't tell me at what load. I asked for the original load calculations, but no one kept them. I just took a picture of the Lochinvar. It is a Knight XL commercial boiler. I can't find the model number on it. It is 399,999 BTUs. We went up from 350,000 B
TUs.

So probably closer to a 325- 350 actual output on a 399. it has a nice turndown, so on the house only load it should be fine.

Whatever you can do to reduce the load on the greenhouse saves $$ as well as plant comfort

EdTheHeaterMan

Looks like the EDR for that radiator section is 9 so the BTU at 180° water temperature is 1,350 each or 12,150 for all 9 of them