Slantfin Hydronic Explorer Accuracy

TimCAD

I used the Hydronic Explorer app to calculate heat loss for a room half below grade I need to heat. It gave me 3793 BTU/H.

I have a similar-sized room directly above the one I'm looking to heat; same exterior walls, marginally smaller square footage. I also ran that one into Hydronic Explorer, and it gave me a similar heat loss (3772 BTU/H).

However, the above room has hydronic baseboard. 14.5 feet of finned tubing, to be exact. Now, at an average (from what I can find) 580btu/h per foot for this standard finned tubing (at 180temp), that would be 8,410btu/h, more than twice what Slantfin suggests I need.

I guess what I'm asking is, for you guys that calculate heat loss often, how accurate do you find Hydronic Explorer to be? If you've used the app and then calculated the same room longform, do they line up? Is it more likely that there's too much radiator in this room, or that I have something input wrong in the app?

Does 3700 btu/r to heat a 195sqft room with 2 exterior walls (2x4 framing) and new, double glazed windows sound like it would be in the ballpark or is that too low?

Rich_49

Is it possible that this room is at the end of a series loop and the original installer calculated for the declining temps through the series , maybe the average water temp is lower due to this ?

Maybe the original designer / installer just used a rule of thumb like sf x 35 BTU / 580 . 195 x 35 / 580 = 11.76 ft . Then you get the bigger is better so I'll just use 2 , 7 footers ?

3700 does not sound outrageous , 19 BTUh per sf is average , maybe a little high .

Keith M

Generally speaking a below grade basement has a lower heat loss per square foot than an above ground room. But it all depends on the construction of the building. In the basement does the above grade wall have insulation?
As far as the heat loss of a 195 square foot room being 3700 btuh...this is certainly possible. It depends on the construction of the house and where you are located. The comes out to around 19 btuh per square foot and I have seen homes with a heat loss of much less. So it depends.
Are you using the correct heat loss factors for each room? Are you taking into account infiltration? Are you using our online heat loss app or the one for a phone or pad?
Please double check your input and selection of heat loss factors. If you have further questions I suggest you contact Slant/Fin Technical Services at 516 484 2600.
We really cannot make an accurate judgement based on the information you gave. There are too many "it depends".
Thank you,
Keith Muhlmeister
Slant/Fin Corporation

Rich_49

ACH ( air changes hour ) do have the largest impact on heat loss .

TimCAD

Rich- I thought of that, but it's smack dab in the middle of that loop XD

Keith- Oh, yeah, I know you need more variables to tell me what it the Heat Loss is, I just wanted to see if it sounded like I was in the ballpark. I was using the android Hydronic Explorer app.

Room is 15.5'x13', with 7.5' ceilings. 2 of the walls are exposed, so 28' of exposed wall length, with a factor of 0.07 (2.x4 framing with insulation). Obviously half the walls are below grade, but didnt see an option for that.

Other two walls are adjoining heated spaces. No cold partitions.

Heated space above, so 0 factor for ceilings. Floor is concrete, below grade grade, pretty sure no insulation below, so I selected 0.04.

One single double glazed window, 8sqft area.

No doors to the outside (just heated spaces) so I left that 0.

Indoor temp 70, outdoor temp 9 (I'm in CT, our average winter low is 17. Forget where I got 9 from.)

Infiltration I'm not so clear on what to pick, actually. Went with 0.018 (room with windows/exterior doors one side only.)

TimCAD

Oh, I got 9F for the outdoor temp from the Hydronic Explorer User Manual, that's where

Edit: I used the Hydronic Explorer website app, same room, same specs, and it gave me 2948btu/h.

I'm so confused XD

Jamie Hall

A 195 square foot space such as you are describing certainly should not be over 5,000 BTUh, and the lower figures which you are quoting sound pretty reasonable to me.

Keep in mind that there are many variables, most of which are rather poorly known -- and so regardless of the accuracy of a heat loss calculator, the results may very, sometimes quite significantly.

Comparing the results which you are getting to that other space with the hydronic baseboard -- it wouldn't be the first time that someone installed more baseboard than was needed. Sometimes a lot more. So that comparison isn't particularly helpful.

TimCAD

Yeah, I hear ya, Jamie.

I'm wanted to use Runtal panels, so I figure if I start where I think I'm supposed to be (according to the calc), and come winter find the room can't get properly warm, I could always just move up to a slightly larger panel with the same length for extra BTU. The distance for the stubouts wouldn't be changing, just the vertical height.

Gordy

Actually that number is probably 20% higher at least than actual real life scenerio.

Keith M

I just calculated it using IBR for this as a basement with 3 1/2 ft above and 3 1/2 ft below grade. Came up with 2,818 Btuh based on your criteria.
Don't get hung up on a small difference.
Remember baseboard is perimeter heat and the more of the perimeter you cover the better. Use lower water temperature to lower baseboard output and minimize short cycling.
Keith

Gordy

The only way lower water temps to emitters works is IF there is more than enough baseboard to cover the load at design day

Some scenarios.

The original installer did the math, and has enough base board. Then an envelope upgrade came later on with wall insulation better windows etc.

The original installer did not do the math, but was paranoid, and installed more than enough baseboard, and a super size boiler to boot.

This is not to say that below design day lower water temps could work with proper control. AKA outdoor reset, and proper boiler protection if a CI boiler is in place.

Rich_49

Keith M said:

I just calculated it using IBR for this as a basement with 3 1/2 ft above and 3 1/2 ft below grade. Came up with 2,818 Btuh based on your criteria.
Don't get hung up on a small difference.
Remember baseboard is perimeter heat and the more of the perimeter you cover the better. Use lower water temperature to lower baseboard output and minimize short cycling.
Keith

BTUs are BTUs . Installing more baseboard and using lower water temps , while a good thing , will not minimize short cycling . Many small differences equal a larger hit on system efficiency overall . Do not overlook any small differences as a rule

Keith M

A longer call for heat does cut back on short cycling,
In a house I used to live in the baseboard was over sized. I reworked part of the house and over sized the new baseboard the same amount as the old. I then installed outdoor reset with the result of improved comfort and lower fuel cost. I saved around 20% on fuel cost with the same 80% cast iron boiler.
Keith