3/4 baseboard how many BTU

Weezbo

Give me a heat source large enough and i could heat the universe with basboard on 3/4" copper.

in a way you are going about the application of what you thought you heard him say...:)

you were probably getting coffee when he was mentioning the heat loss part....

Lakewood

I went to Dan's course on hydronics and I think he said that you could only get 40,000 BTU out of a 3/4 pipe. If so how can you run 100 ft of baseboard?
Secondly, how long should it take a house to warm up from 40 deg on a cold night (20 deg) if you are using baseboard? Its been taking 12 hrs and it only went up 20 deg?

bobbyg_9

the 3/4" baseboard element I deal with is 580 btu's per linear foot with 180 deg F entering water temp with 1 gpm.

I believe what Dan was referring to is the fact that with 3/4" copper the maximum recommended flow rate is approx. 4 gpm, which is approx. 40,000 btu with a 20 deg F delta t (temp. drop).

Tell us more about your situation with the house no heating up. Like size of boiler, water temp., estimated flow rate, linear footage of basebaord, heatloss of building, design conditions...

Hope that helped.

Brad White_185

Weezbo and BobbyG got your back

on the essence of it. The carrying capacity of 3/4" pipe and how much element you can run in a given circuit are two different questions.

Typically I keep the 3/4" element runs to 30 feet or less and maybe 40 feet on the commercial sizes.

This is not a limitation of the carrying capacity of the pipe but that at the end of a long run, the output can start to drag... If you run stacked element however, with the supply on top, the overall output will be "mathematically even" (the average water temperature is the same no matter where you draw a line through the stacked elements) and you get about 30% more output.


Now, as to how long it will take you to warm up a house from a cold start? Depends on the amount of radiation you have relative to the heat loss and the size of the boiler to drive it. Also the supply water temperature. (Some systems using outdoor reset which depresses the supply water temperature below it's hottest, can prolong a warm-up cycle greatly.) You do understand that you also have to warm up the houses mass too, not just the air inside it. It must have been way cold for way too long.

12 hours seems to long so I would want you to make sure that you have enough radiation. Burning 12 hours worth of fuel input is huge for that small benefit.

realolman

how can

you decide what IS an appropriate setback? I think it takes a long time to recover from setbacks at my house.

How can I decide at what point it's costing me more to recover than I saved by setting back?

Brad White_185

What I do

If you can latch on to a data logger this is a lot easier.

Measure outside temperature and inside temperature over time, say every minute if you are measuring over one night, every five minutes if you are doing a few nights. (This is to balance accuracy with the data logger's capacity.)

The outside temperature data helps because it drives how fast the house cools off. Discount wind for the moment to keep this simple.

For these experiments I "drop the bottom out of the thermostat" or at least set the setback temperature lower than you normally would to get as much "contrast" data.

Graph out your results. Note how fast the "drop slope" goes from the time the system shuts off. Then note how fast (or not) the "up-slope" goes during recovery to occupied or daytime temperature.

Draw a vertical line from the lowest temperature to the starting temperature and color in that "wedge". Do the same from the lowest temperature to the recovered temperature and color in that wedge in a different color or pattern. You can graphically see how much energy was saved (the downslope time when the boiler was off) and how much was spent before the house was again comfortable.

On average, I see these as being nearly equal but if the house is leaky and the heating system (say radiators versus boiler) is sub-par, there is a fast drop and slow recovery. If the system is hugely over-sized, recovery is faster of course.

In short, unless I am away a week or more, I only set it back to what temperature occurs after two hours of off-time. Mostly because I like to sleep in a cooler room than anything else.

You can imagine the number of variables in play here, especially outside temperature.