What should Slant Fin Baseboard Water Temp be for whole house heating?

Crissie

Application is a new boiler system install for hot water heat using all Slant Fin baseboard. House is 2800 sq ft, three zones, one zone for each level of house. In Chicago area, winter temps are cold. No under floor heating, all slant fin. What water temperature should be used in the design? I am trying to hire someone to do this and he is using 160 degree in his design. Any thoughts?

EBEBRATT-Ed

Basically first you do a heat loss of the building.

Then you pick the water temperature you want to use.

Baseboard systems typically operate at a 20 degree temp difference. That's because water may leave the boiler at 190 (for example) and return to the boiler at 170 after giving off it's heat in the baseboard

So to size the baseboard footage you would use the average water temp which would be 180 in the above example.

190-170=180 average is the highest temp I would use.

The higher the average temp you use the lower amount of baseboard would be installed

The lower the average temp means you install more baseboard to match the heat loss and lower water temp=lower fuel bills but higher installed cost due to more baseboard.


So like everything else it is a compromise. Some rooms you may have limited wall space for more baseboard etc.

So a house with a heat loss of say 90,000 would need about 163 ft of baseboard roughly

So if he is using 160 average (170 out-150 return) that's fine if you have room for the baseboard.

Baseboard is made in different sizes, some has higher or lower output

Crissie

Wow, makes total sense. This is why he sized it for so much baseboard. We are using the Slant Fin Baseline. Does water GPM come into play at all? This is all based on personal preference, yes? I prefer not to have multiple entire walls completely lined with baseboard.

EBEBRATT-Ed said:

Basically first you do a heat loss of the building.

Then you pick the water temperature you want to use.

Baseboard systems typically operate at a 20 degree temp difference. That's because water may leave the boiler at 190 (for example) and return to the boiler at 170 after giving off it's heat in the baseboard

So to size the baseboard footage you would use the average water temp which would be 180 in the above example.

190-170=180 average is the highest temp I would use.

The higher the average temp you use the lower amount of baseboard would be installed

The lower the average temp means you install more baseboard to match the heat loss and lower water temp=lower fuel bills but higher installed cost due to more baseboard.


So like everything else it is a compromise. Some rooms you may have limited wall space for more baseboard etc.

So a house with a heat loss of say 90,000 would need about 163 ft of baseboard roughly

So if he is using 160 average (170 out-150 return) that's fine if you have room for the baseboard.

Baseboard is made in different sizes, some has higher or lower output

Wow, makes total sense. This is why he sized it for so much baseboard. We are using the Slant Fin Baseline. Does water GPM come into play at all?
This is all based on personal preference, yes? I prefer not to have multiple entire walls completely lined with baseboard. I'm planning for a cast iron boiler with secondary stainless steel heat exchanger, 92% efficiency. Not as interested in saving a little gas. I prefer the 180 temp. The Slant fin product says it is rated for 600 BTU / ft at 200 degree temp. My contractor is rating it at that 600 BTU / ft at 160 degree temp. Not sure if that is an error.

EBEBRATT-Ed

If he is using 600/foot at 160 and Slant fin says it's 600/ft @200 then he is wrong. 600 @200 sounds low to me but if the spec sheet says that then thats what it is.

Everything has to be done in sequence

Heat loss first
pick the average water temp
size the baseboard footage
make a piping layout
GPM
Pick boiler

The gpm is determined by the footage of baseboard on that zone or part of a zone depending on how it's piped

so if you had 30' of baseboard @600 btus/foot=30x600=18,000 btus

every GPM of water that drops in temperature 20 degrees (the std temp drop for baseboard) will give off 10,000 BTUs

So from the example above 18,000/10,000=1.8gpm

a boiler with an output of 100,000 BTUs the required flow rate would be 100,000/10.000=10gpm

Hot water heat is grat if done right. Much superior to forced air JMHO

mattmia2

You could use different types of emitters like panel radiators if you want to decrease the amount of space they take up. Fin tube baseboard is very cheap and unobtrusive but has a relatively low heat output per foot. You wouldn't want to use more than about 180 degree swt because it can cause problems such as cavitation in the circulator.

CMadatMe

Its all depends. Heat loss of individual zones, which Slant Fin BB product is used as well as circulator choice. Fine Line 30 at a 1gpm flow rate will provide 580 btu/hr using 180 degree water. Slant Fin 80 (w/H3 Element) at that same flow rate with 160 degree water will provide 570 btu/hr. I would disagree that 20 degrees is the standard temp drop across baseboard as well as baseboard footage determines flow rate. Yes, it provides for easy math but in the real world most residential baseboard systems are running at a 10-15 degree drop or less thanks to that pesky fixed speed Taco 007 or what ever flavor equivalent is used.

Ctoilman

Strongly consider the Slantfin Multipak 80 baseboard heat.  It's much more robust and puts out more BTU per foot than the 30 or 2000 series, which means less total linear feet of heat.  But I'd rather have more baseboard heat and have the boiler running at lower temperatures yet still heating the home.  

Crissie

Ctoilman said:

Strongly consider the Slantfin Multipak 80 baseboard heat.  It's much more robust and puts out more BTU per foot than the 30 or 2000 series, which means less total linear feet of heat.  But I'd rather have more baseboard heat and have the boiler running at lower temperatures yet still heating the home.  

Even a cast iron boiler?

Canucker

Crissie said:

Ctoilman said:

Strongly consider the Slantfin Multipak 80 baseboard heat.  It's much more robust and puts out more BTU per foot than the 30 or 2000 series, which means less total linear feet of heat.  But I'd rather have more baseboard heat and have the boiler running at lower temperatures yet still heating the home.  

Even a cast iron boiler?

Yes, even for a cast iron boiler. The difference is the minimum return temperature that the cast iron requires. Don't use so much baseboard that the return temps fall below that temperature for extended periods, otherwise your heat exchanger is going to rain and it won't last long

Zman

If you really want to dial it in, size the downstream baseboards for the lower water temp.

HomerJSmith

If you are worried about raining on the HX, do this. I have used a Taco I-Series set point mixing valve with a sensor in a bypass arrangement and it worked very well. The sensor kept the return water to the boiler at about 135 deg, minimizing start up and sustained gas condensation. (copied from another post)

hot_rod

panel rads would be my first choice, you get radiation, and convection output, conduction also if you sit on thjem They feel great when you sit or stand next to them.
Fin tube is mainly convection currents. Several fin tube brands have low temperature high output options, like the heating Edge and other.

I'd like to see all hydronic systems designed around a 120°F or so SWT.