Slow Heating Downstairs

bsavage0488

Hello! I was just hoping to get some help with our current system...

We have a Navien NCB-240e on a two-zone system with Taco 007e circulators and baseboard heating.

Our downstairs is having trouble maintaining the set temperature (it's set to 68, but doesn't get above 65 or so). It's pretty cold here this week, plus a leaky house, is probably a contributor -- and maybe everything is working as it should.

While the output is generally pretty close to the range we've set (set at 180, output in the mid 170s), the return is higher than I would have expected (~165 degrees), running at 26.1psi.

Just my novice speculation, but is the system pushing water through the baseboard at too high of a rate, so the heat exchange isn't able to occur fast enough?

Should the PSI be lower, or can the circulators turned down somehow (I don't see any switches)?

EdTheHeaterMan

PSI has nothing to do with it. But the flow rate might. You are striving for a 20° drop from supply to return if the baseboard elements are near the maximum allowable length. (near 60 to 70 feet of element) If the zone is much smaller or there is blockage of the airflow across the element then that can be your problem.

I had a customer with wall-to-wall carpeting installed so there was no room for airflow under the baseboard. I was guaranteed a service call every year when the temperature dropped to below 15°F for several days in a row. That is because the airflow across the elements was enough to heat the home as long as it did not need more than say 60% of the radiator's capacity. As the outdoor temperature dropped below 15°, the restricted capacity was insufficient to keep up with the demand.

I would walk in the home and see the restricted radiators, go to the boiler room and see everything functioning, the circulator was pumping heated water, and the burner was cycling off the high limit. I told the customer about the carpet, said there was nothing I could do, and charged for the minimum service call fee.

After the third year of charging the customer to tell him the same thing, I added a big note to the file so when the customer's name came up on the computer screen I would know to look at the outside temperature and ask if the carper was trimmed back from the radiators yet? If they said NO, I would ask if they wanted to pay for a service visit to tell them to trim back the carpet again? That saved me a trip and the customer some money. You just can't fix stupid.

Respectfully Submitted
Mr.Ed

bsavage0488

That makes a lot of sense! Most of the baseboard run is pretty unrestricted, however the last 10 feet has a couch pushed up pretty close to it (pretty close meaning at the bottom, it's ~ 4-5 inches away from the baseboard, but at the top of the backrest, there's only ~2 inches of space from the wall).

I wonder if either pulling the couch away or increasing airflow behind the couch (by way of a fan?) would help.

EBEBRATT-Ed

@bsavage0488

Yes. Keep the furniture away from the baseboard. Make sure the baseboard is clean, they collect a lot of dust and cat hair even if you keep the house clean. And make sure the dampers are wide open

Having too much flow through the baseboard will actually increase the output very slightly. No harm there but it's possible on the other end it could affect the boiler and it's controls causing the boiler to cycle instead of staying on.

get a thermometer and check the water temp in and out of the baseboards will give you a better idea of what is going on

EdTheHeaterMan

You don't need a fan @bsavage0488. They are not designed as a forced-air system. Checking to see if the underside of the elements are clear is a good idea. Since the convection currents are UP at that point. light stuff like animal dander, dust bunnies, and construction residue (if recently remodeled or spray-painted during the heating season) will stick to the BOTTOM.

Good observation @EBEBRATT-Ed I have always said that 2 Eds are better than a sack of potatoes.

HomerJSmith

It seems counter intuitive that high flow speed could have something to do with heat transfer except make it better. We all know that too slow a flow will reduce the heat transfer.

But I did read, and don't ask me where, too fast of a flow will reduce the heat transfer. I think it was because of the boundary layer. One need to stay within the 4gpm flow rate for 3/4" baseboard.

Has this always been a problem or a recent development?

If one has insufficient heat energy to meet setpoint, the following could be the problem.

Insufficient baseboard to transfer heat into the environment that's loosing it to the outside.

Too low of a supply temperature.

Restriction in the flow thru the baseboards.

Insufficient flow thru the boiler, pump, or baseboards of water and insufficient flow of air across the baseboard.

A return temp differential of 10 deg is not what I would want.