Determining Needed Baseboard Radiation

Here we go again with another Sunday fun day conversation starter.. I thought this was very exciting!

So as you guys may know, I plan to make the switch to 100% hot water baseboard heating. Currently I'm using a huge water to air heat exchanger to heat the entire downstairs with 16ft of baseboard for the 2 bedrooms upstairs.

Recently I determined my heating requirement to be ~ 47.5 pounds per day (which excludes DHW) with an average OAT of 34 degrees. This equals about 1.5 pounds of coal per heated degree based on heated to 65 degrees in the house.. Of course we like it warmer than that, we run the thermostat 73 during the day and 71 at night.

Ok.. so given we need 1.5 pounds per heated degree we can estimate our daily usage at the system design temperature of OAT at -2 degrees Fahrenheit. So, based on heated to 65 degrees in the house we need 67 degrees worth of coal at 1.5 pounds per degree. This arrives at about 101 pounds per day with an OAT of -2 degrees.

Given this information above, we now can get a really good idea of how many ft of baseboard the entire house will need. We'll use 10,000 btu per pound to factor 80% efficiency of the Axe and keep things simpler. At 101 pounds per day at design temperature of -2 we should require 1,010,000 BTUs. This works out to be about 42000 BTUs per hour which then translates into a requirement of 84 ft of baseboard that would need to run nonstop at a design temperature of -2 degrees OAT.

84 ft... why is this interesting? I also used the Omni heat loss calculator app and input each room size, number of windows, doors, exterior walls and factors insulation.. That app calculated a need of 82 ft total in the house at -2 design temp.

I was very shocked that my real world usage lined up so closely with a heat loss calculator..

Who'd a thought??

I should add that there is one other variable I did not account for.. this would be the outbuilding. We've only been keeping the outbuilding at 40 degrees which is only 6 degrees above the average OAT for that period. The outbuilding has a couple little refrigerators and other electrical things that also generate a small amount of heat. So I estimate that only a tiny amount of heat went down there. Probably the additional 2 ft of baseboard requirement I came up with

You also have to factor in the design temperature of the water.

Degree days are based on a 65 degree average outside temperature because with that average outside temperature no heat will be needed inside.

franco b wrote: ↑

Sun. Jan. 09, 2022 12:57 pm

You also have to factor in the design temperature of the water.

Right! I figured 500 BTU per foot. I'm not exactly sure what the boiler temp needs to be for that. Some baseboards are better than others also

franco b wrote: ↑

Sun. Jan. 09, 2022 12:57 pm

Degree days are based on a 65 degree average outside temperature because with that average outside temperature no heat will be needed inside.

Yes, the first 5-7 degrees are heated by people, refrigerator compressors, computers, TVs, ect.. they all contribute heat to the house.

The literature for the particular baseboard should give the BTU rating for different water temperatures.

Length of baseboard required will vary decoding on temperature of water, and model of baseboard.

Most baseboard has literature with the output per ft at different water temps. I prefer high output baseboard, which puts out about 50% more buys per foot.

Lightning wrote: ↑

Sun. Jan. 09, 2022 12:45 pm

Here we go again with another Sunday fun day conversation starter.. I thought this was very exciting!

I feel more enlightened already... I'm not sure what that says but

Anyway, that would also mean your building heatloss is "average" or is the factored amount correct, I don't know if that's good or bad?

I'm with Rob on the higher output baseboard. Higher upfront costs, but better to turn down than run out of capacity, or require higher water temps to get the output you need.

Zoning will make a difference in your required BTUs.

Heatload calcs depend on heat going ONLY where it is needed. Better targeted zoning and controlling the length of runs makes a difference.

Splitting the supply and return per zone can keep more of your baseboard at the higher supply temp vs running in one big series and the lower temps and output of baseboard farther down the line in a series.

IMHO, make the distribution as efficient as possible (multiple zones, splitting supply/return lines, higher output baseboard, insulation) and then work on the supply end, being the boiler and controls.

Chances are good that you tweak and modify the supply end in the future, but likely never change the distribution side after it is installed, so do that part right in the beginning.

High output baseboard costs more per foot, but you need less of it.

I know you guys mean well with the top shelf baseboard but they're pretty expensive. The Slant fin Base line 2000 is only about $10 per foot and delivers 500 BTU at 170 degrees. This still leaves me wiggle room to turn the boiler temp down to 150-160 until it goes below 15-20 degrees outside, then I'd be forced to run it between 170-180 to get 500 or more BTU per foot. I don't mind turning up the boiler temp if I need to since its in the basement (standby loss contributes to heating) and the boiler and piping is mostly insulated. Plus I'm thinking that using more instead of less footage will spread out the heat distribution more evenly. I'll give it more consideration but I think the Base Line 2000 will do the job, plus I already have 36 feet of it ready to put up. Some of it was a facebook market place find that I got quite below cost The 81A baseboard puts out 40% more BTUs but costs about 125% more.

Also! We have the Hitzer 503 insert for auxiliary heat when it goes -15 every 10 years

I currently have the upstairs bedrooms on one zone. The downstairs will have at least 2 zones possibly 3.

Thank you for the fine advice fellas!

What would you say is the max baseboard footage on one zone considering its all 3/4 inch? I imagine it depends on gallons per minute but I have no idea how to measure that.

Lightning wrote: ↑

Sun. Jan. 09, 2022 7:38 pm

What would you say is the max baseboard footage on one zone considering its all 3/4 inch? I imagine it depends on gallons per minute but I have no idea how to measure that.

If you use split supply and return, you can use more feet of baseboard, since twice as much of it will be at full supply temp. Your supply is 1" and extends to roughly midpoint of your zone, tees off to two 3/4" runs of baseboard. 1" carries more BTUs

How many feet are you considering per zone?

Lightning wrote: ↑

Sun. Jan. 09, 2022 7:38 pm

What would you say is the max baseboard footage on one zone considering its all 3/4 inch? I imagine it depends on gallons per minute but I have no idea how to measure that.

It depends on flow rate and type of baseboard. Please see attached for rules of thumb on this.

Also, some good reading here: https://heatinghelp.com/systems-help-center/loop- ... g-q-and-a/

Measure flow by doing...
https://www.nationalcomfortinstitute.com/pro/file ... ystems.pdf

CoalisCoolxWarm wrote: ↑

Sun. Jan. 09, 2022 8:59 pm

If you use split supply and return, you can use more feet of baseboard, since twice as much of it will be at full supply temp. Your supply is 1" and extends to roughly midpoint of your zone, tees off to two 3/4" runs of baseboard. 1" carries more BTUs

How many feet are you considering per zone?

Oh wow.. I didn't think of that but it makes really good sense!

My biggest zone will be the living room which used to be a garage. It has 3 exterior walls and seems to require a lot of heat. The heat loss calculator says to use 36 ft but I'm inclined to put in 45, 15 ft on each exterior wall. So 45 ft would be the longest zone.

I'm not sure what to do with the kitchen. Its in the middle of the house with only 1 exterior wall. The heat loss calc says it should have 1530 BTUs worth but I'm struggling to find a place for it. Would it make sense to add a little baseboard to the adjacent rooms instead?

Then there is the far room on the other side of the house. The boiler room is directly underneath it. It current has no heating but only feels slightly cooler, its also where the cold air return is so heat gets dragged out there after being pulled thru the kitchen. But of course that won't be the case once its not windy in here anymore. I'm considering giving that room its own zone so that I don't overheat it since it gets some radiant heat from underneath. My cat loves to lay on the floor directly over the Axeman, a sure sign that he's found a warm spot

Lightning wrote: ↑

Mon. Jan. 10, 2022 3:45 pm

I'm not sure what to do with the kitchen. Its in the middle of the house with only 1 exterior wall. The heat loss calc says it should have 1530 BTUs worth but I'm struggling to find a place for it. Would it make sense to add a little baseboard to the adjacent rooms instead?

Just a thought I had, but what about a through wall vent or two located between rooms? I know some are powered but for as little BTU input you need, that might be the ticket?