How many BTUs

Harry_Harry2

I am a customer of the Columbia Gas event that happened in Lawrence, MA. They replaced my 30,000 BTU gas space heater in my basement with a 10' section of baseboard, but it never quite gets to the temp I set it at on really cold days. Can anyone tell me if they installed the right length of baseboard to replace my space heater? The boiler is a combi Navien and I think the piping is 3/4".

Brewbeer

No, they did not.

Typical baseboard puts out about 500 BTUs per foot. If your 30,000 BTU gas heater was 67% efficient and supplied 20,000 BTUs into the space, you would need about 40 feet of baseboard (40 ft x 500 BTUs/ft= 20,000 BTUs) to equal the output of the space heater.

Lots of assumptions above, but it's pretty clear 10 feet of baseboard is not equal to what you formerly had.

SuperJ

What you had, have, and what you need are likely three different numbers. I would start with a heat loss calc on the space, and then go back and argue for a properly sized emitter (baseboard).

Online heat loss calcs:
loadcalc.net or http://www.hydronicexplorer.com/Login or two options. Loadcalc is a more accurate and will give a lower (often 20% lower) number but requires more careful use.

Gordy

The argument is cut , and dry. You had a 30k gas space heater, and now you have a 5k btu baseboard. Before the space heater did the job, and now the baseboard does not. That 5k is at 170 average water temp. For the navien to get its highest efficiency you need to get the return water temp down to 130 minimum.

Is the rest of the house base board?

One other thought also is what is the supply temp to the baseboard the navien is providing.?

Gordy

To lower return water temp the emitter needs to be over sized so a lower awt can be used.

Harry_Harry2

house is now all baseboard with 3 zones. Temps range from about 167 to 185 and pressure runs between 18 and 30. Baseboard is Slantfin and the Navien is 95% efficent according to the label on the unit.

Jamie Hall

Harry_Harry2 said:

house is now all baseboard with 3 zones. Temps range from about 167 to 185 and pressure runs between 18 and 30. Baseboard is Slantfin and the Navien is 95% efficent according to the label on the unit.

Ah... unless this is a very tall house, the pressure is too high. And that efficiency statement assumes that the return water temperature is in the range around 120 or so... which I doubt that yours is.

Gordy

You also are not getting 95% efficiency out of the navien.

Harry_Harry2

The 167 to 185 is the delivery temps the return runs 120 to 130. So that would make my efficiency 93%?

Voyager

89 - 93%

EBEBRATT-Ed

Unfortunately those jobs went in at breakneck speed. The company I work for did some work their. The quality of work from all contractors (out of town & out of state travelers did a lot of the work supervised by MA contractors) is probably ok and was all inspected.

The equipment selected the contractors had nothing to do with that. They just installed what they were told.

From what I herd replacements were based on what was installed before. Not the best but what do you do? The scale of this job was massive

Gordy

So the system delta is 47-55:degrees for an average water temp of 143-157*. I assume the outdoor reset is hooked up?
My point is with such a large system delta the awt going through the emitters is low which is great for the boiler, and not so good for comfort, or not reaching set point, since the emitter output is lower.

hot_rod

It could be that they have a long string of baseboards in series, so SWT drops thru each section. That can work as long as the last baseboards in the loop are sized larger to give sufficient output at the low SWT they will see.