Supply & Return Both Very Hot, Minimal Heat from Baseboard

NTL1991

The two heating zones in my hot water baseboard system are working perfectly. That is, the 2nd floor and 1st floor of the house. There's a boilermate on another zone. Finally, I've got a 20' x 14' four-season patio on another zone.



Supply water temperature is 180 degrees, being produced by an oil-burning Utica 175 MBH boiler. The boiler has been down-fired to about 125 MBH.



The problem is that I'm not getting sufficient heat output from the baseboard in the patio. The Delta-T of the the loop is far too small, just about a few degrees. It was designed for a 20-degree Delta-T. The return pipe (which sits on top of the fins) is actually hotter than the fins themselves. There's no air in the system, and the finned-tube is straight and clean.



This zone is comprised of roughly 20 feet of Haydon 3/4" finned-tube baseboard, which the return loops back over to get to the boiler. The circulator is a Taco 007-F4.



I'm thinking the circulator is moving the water too fast when only the patio is calling for heat. I haven't tried making a call on the 2nd floor (which rarely is turned on) and 1st floor at the same time the patio is on. Perhaps that will drop the GPM through the patio loop, and allow some BTUs to pass on to the fins, and then the air.



Maybe I should think about a Delta-T circulator? Any ideas?

Mark Eatherton

Slowing the flow won't change much....

There are things at work that the minds eye has trouble seeing, like Reynolds numbers, average temperatures etc.



THe fact that you have hot water flowing across the baseboard indicates to me that you have flow. You can confirm this by carefully quickly closing a ball valve serving that zone. If you hear a hydraulic HISSss as you close the valve, you've got flow. Need to look someplace else for the cure. If no hiss, no flow.



Look carefully at the finned tube elements. Some are closed on two sides. If the finned tube element was improperly installed (turned 90 degrees), then even with hot water flowing across the convector, it the element can't breath, then few btu's drop off the pipe and into the air.



Maintaining a high average temperature across a given convector is a good thing as it pertains to delivering heat. I do not believe that you can run the water across these elements too fast (exclusion being errosive velocities).



There is this misnomer that by slowing the flow, and getting a higher delta T, that the emitters are actually delivering MORE energy. Wrong. Delta T is dictated by the load and the emitters. The only way you can increase the delivery of btu's is to either increase the load (leave windows and doors open) or increase the heat emitters surface areas to deliver more heat.



Which moves more energy, a pipe moving 1 GPM at a 100 degree F rise, or a pipe moving 100 GPM at a 1 degree F rise???



I'll let you do the math on that one :-)



Good luck.



ME

NTL1991

Thanks, Mark

Thank You, Mark. Very well said.



I have seen that very problem with incorrectly installed baseboards before. Had to carefully rotate them all over. Luckily it was only on a 4-foot section... It was REALLY cutting heat output... That's not so in this case, though.



I know I'm getting flow in this zone, so the only thing I can think of is air not being admitted into the baseboard... What is the minimum clearance of the finned tube off the finished floor (carpet in this case)? Or is it better to measure the clearance of the front cover off the finished floor?



Perhaps the finned-tube elements are too close to the carpet, which would cut off its air supply?

Mark Eatherton

Clearance Clarence...

I typically defer to the manufacturers literature, but like to see a minimum of 1" inlet on the bottom. It is also quite common for carpet layers to get lazy and put the carpet in in such manner that it completely blocks air flow to the fin tube elements...



Pull the cover, and look carefully.



And you are welcome.



ME

icesailor

Delta "T" and the brain:

Sometimes, some get Delta T on the brain.

If the supply to the baseboard is through the element and returns over the top (as it should), it is physically impossible for the top/return to be hotter than the bottom, the supply. Unless it is piped so that the supply is on the top.

How are you measuring this Delta T? If you can feel that one pipe is hot and the other is cooler, and the temperature measured someplace is very close ( as you say), you must be measuring it in the wrong place. You may have a piping problem where flow is going where it wasn't designed to go.

Delta T doesn't mean squat unless you know what the pressure change through the loop. Unless it has a dedicated circulator for the zone in question with gauges on either side, the flow is just an uneducated guess. If you pipe 50' of 3/4" fin tube baseboard and pipe too and from with 1/2" tube, you will get a much higher difference on temperature between the supply and return. Because you can only get so much water through a 1/2" pipe. Change it to 3/4" pipe and you will see the return temperature go up.

If the room gets warm, what is the problem? If the room doesn't get warn, then, why? Delta T is just an indication of a problem that may or may not need to be addressed.

icesailor

Carpet Munchies:

Oh, glad that came up.

ME is absolutely correct about flow and other things.

About carpet. Look to see if the bottom of the Fin tube baseboard back cover is sitting on the wood sub floor and the carper is on top. Whenever I do baseboard, before carpet goes down, I lay a 2 1/2" strip of flooring,wood, 3/4" in thickness and install the baseboard on top of that. The carpet installers MUST use a tack strip in front of the board, and the baseboard has the proper, designed opening. It is really bad when they run the pad under the baseboard and the carpet on top of that.

I've raised up the whole baseboard to stop the problem. I still don't understand the bottom being cooler than the top though.

Steamhead

Au Contraire, gentlemen

it is definitely possible to over-circulate baseboard. I've seen it happen- sure, the books say it doesn't matter, but still it does happen.



A quick way to see if this is a problem is to partially close a valve on that loop. If that cures the problem- not the ΔT problem, but the lack of heat output in the room- then we know for sure.



Also, something more basic- are the baseboard's fins plugged with dust?

Mark Eatherton

I've never seen that Frank...

Not to say that it can't happen, but based on Reynolds numbers, it doesn't sound possible.



But as I've said, I've not seen EVERYTHING, but have seen a LOT of things, and thats not one I've experienced.



ME

NTL1991

2 Layers or Carpet

According to my father, the house had a layer of carpet with padding before the baseboard was installed. They replaced the carpet, but had it installed right over the old.



Tomorrow I'll check the clearance. There might be a tack strip under the baseboard, in which case I can unscrew the baseboard and raise it a bit if the piping has enough play.



The baseboards are clean and free of debris, and are installed in the correct orientation. My first thought was that the fins were packed with fur and dust, but they weren't.



At the near boiler piping, the supply and return pipes for this loop are VERY close in temperature, ie low Delta-T. There's got to be a reason the 180 degree supply water isn't giving up it's BTUs to the air...



The whole loop is piped with 3/4" copper. The return runs from the last finned tube element, and loops up and runs over the fins back to the basement. It seems as if the copper pipes are heating more air than the fins.



The problem is that the room takes too long to heat up in the morning. Solar gain is very good during the day, and keeps the house at a relatively even temperature, but the initial warm-up in the morning takes quite a long time. You can tell that the BTU output from the baseboard isn't as much as it should be with 180 degree water.

NYplumber

Crimp'ed

More than once have I seen 3/4 pipe crimped with a channel lock. What the reason was, I have no idea. But it comes to show you how 3/4 isn't always 3/4. The same applies if less than full flow valves were used.

icesailor

Rugs and Baseboard.

You really need to look at that carpet, carefully. Its really a very common thing. They nail the tack strip in front of the baseboard and run the pad to the carpet strip. They can not get the tack strip under the heaters. They then fold the carpet under the baseboard and usually run the carpet as far as it goes by where they cut the carpet. I've seen carpet right up to the bottom of the front cover.

Carpet installers are not the bulb at the top of the tree. One once split and ripped out the wood strip I installed the heater on. All he had to do was fit the carpet strip to the wood strip, and tuck the carpet. But because he only knew leaving the pad out, and sliding the carpet under the baseboard, he ripped out the strip.

Go Fig're

Paul48

heat loss

I think if you do a heat loss for that room, you'll probably find you don't have enough radiation. Marginally insulated, with double-pane windows, and a lot of speculation on my part.You should be around 15-16000 btu's with your emitters.You're around 10000. Again, this is with a lot of speculation, but may not be too far off the mark.

hot_rod

I suspect inadequate radiation

also. The best first step is a load calc, without knowing the actual load you cannot know if you have enough board to heat the space. A converted patio??? Hmmmm.



Here is a link to a hand, load calc sheet. Thanks to the pikes Peak Building Dept.





www.pprbd.org/plancheck/Heat%20Loss%20Table.pdf

icesailor

Heat Loss:

Proper emitters is a given. No mention was made of the unit being too small. The carpet issue came up in the beginning. If the carper is installed improperly in relation to the baseboard emitter, then that neess to be fixed before anything else. I personally would have done  heat loss calculation on the room to know what I am dealing with. I've seen this happen way too many times.

Cast Iron Base Ray baseboard was always installtd on a solid floor. They had a diagram on how to install if a rug was being used. To put down a wood strip tp raise the baseboard so air could run up behind the baseboard. If you installed it on a wood floor, it set on the floor and was fine. I got quite a few calls in the past where a room wasn't heating properly. I'd find that the carpet installer had run the carpet into the bottom space and stopped all air flow through the back of the baseboard heater. The other PITA was with Sunrad radiators. The rug was run under the radiator and the front grill no longer fit. And cutting it down made it so it wouldn't fit.

Hackaroos.