getting more heat out of baseboard heaters


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Old 02-02-11, 11:01 AM
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getting more heat out of baseboard heaters

We are in the midst of a cold spell. It has been -17 F for 2+ days. I realize we only get this cold maybe every 5 years or so. My situation is only exacerbated now.

I think I have a case of simply not enough baseboard to properly heat the area. For the last two days one zone has not shut off and the area cannot get up to the thermostat setting. The temp is adequate 66 but not the 70 requested. This zone always has a hard time coming up to temp.

Thanks to this forum I have learned enough to make these statements. I believe the boiler is not undersized as it does cycle. It is set to 200 high and drops to 155-160 before coming back on. There are 5 zones plus an indirect water heater. All the other zones will open and close as the heat call is satisfied. When this is the only zone open the return temp differential is 10 +/-. When several zones are open the return is rarely more than than 20. There is a system bypass valve adjusted to a max 20 degree differential for the longest zone by itself. There is one circ pump Taco 007. The longest zone is about 180' including 30' of baseboard. I have a new aquastat on order. It has an adjustable differential which I will set to 30 instead of the current 40-45, sometimes dropping to 130-135 before starting.

My assumption is there is not enough baseboard in that one zone. The units have been cleaned, the fins are not bent or otherwise obstructed. The thick pile carpet is tucked under the bottom edge of the back plate as per design. Most of the baseboard has no furniture against it. One couch backs up to one section, but is 14" away.

Is there a way to get more heat out of this zone? Would a fan blow along the baseboard face increase heat to the room? I am not interested in major changes costing lots of unavailable money. I want to get the most out of what is there.

Long term, I want to improve this zone. All available wall area has radiator. There are several doorways, halls, and room openings. I assume this means we have to replace the standard 3/4" Heatrim American baseboard with higher output baseboard.

Any suggestions on how to otherwise tweak this system for more heat in that one zone?
 
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Old 02-02-11, 12:54 PM
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Two ways to approach this problem:

1) add more heat

2) reduce the loss of heat

I prefer 2....

For 1, if you have an available place to add baseboard, you probably can. 3/4" pipe can carry around 40k BTU/hr. So long as your total fin-tube element length doesn't exceed this for the zone (figuring about 550 BTU/hr/ft, i.e., about 70 ft), you can.

For 2, get a tube of caulk and caulk around the windows. Also caulk around exterior and interior doors (even interior doors can leak air through stack effect up into the attic or elsewhere). If you have access to the attic space over the problem zone, spray foam all the top plates and foam up all plumbing and electrical penetrations. Buy a bunch of outlet gaskets and install behind all your switch and outlet faceplates. Add insulation anywhere you can.

You'd be amazed how quickly this stuff adds up to improve comfort/temperature. Especially reducing the infiltration (drafts).

And no, don't blow a fan across your baseboard. Blowing air adds to the existing heat loss and won't coax much if any more output from the baseboard.
 
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Old 02-02-11, 01:07 PM
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xiphias

I have lived here for 20+ years and have buttoned up the home well. Did a blower door test and had less than 1/2 air change per hour. Even added insulation to the entire exterior of home while adding new siding. I am confident the home is well winterized.

My issue is trying to coax more Btu's out of the existing baseboards in the short term. Then I will have to replace the baseboards with higher output ones as I do not have more wall space.

Is my system tweaked or can I do more?
 
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Old 02-02-11, 02:02 PM
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Is you bypass piped properly? At 200F your tweaked, but I never saw a 40-45F diff on a aquastat. Whats the model # of the aquastat? If its cold your working off the HI limit anyway and most have a 10F diff. The low only comes into play when there is no call for heat.

So how are you piped? One heats return water, and one cools supply water.



Bell & Gossett - The Ins and Outs of Boiler Bypass Lines

Mike NJ
 
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Old 02-02-11, 03:27 PM
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Seems that the problem is if you don't have enough emitters to counter the loss, there really isn't a whole lot you can do at this point.

If you only have a 10 DT on that zone, then it would seem that there isn't enough emitter.

I think that 'stretching' the DIFF is a losing battle. You are allowing the boiler to cool more, sending cooler water into the zone for a longer period of time. Try tightening the diff a bit and see what happens... yes, the boiler may cycle a bit more, but it's a compromise you might be justified in making... at least for this really cold spell.

What IS the heat loss of the room? And how much element is installed?
I haven't used, or seen in person, the Smith baseboard product, but was impressed with the heat output ratings. They are said to do with 110-120 water what Slant Fin does with 180 ... and at 180 they are more than double the Slant-Fin. Slant-Fin also has higher output units, look at the 'Multi-Pak' series. If you notice the pic on this web page, they are mounted pretty high off the floor... I understand that this will allow a slightly higher output from ANY baseboard, probably due to a bit higher airflow through the cabinet. Check 'em out here:

Smith Environmental Products Hydronic Baseboards. The Heating Edge Hydronic Baseboard. Hydronic Heating Systems - Radiant Heating System, Solar Heating, Geothermal Heating

While on GP's I do agree with Xiphias that a fan probably isn't the right thing to do, I think that if you could somehow 'duct' a low CFM flow into the bottom of the cabinet that it would boost the output somewhat. Just blowing a fan on them won't help, and might actually hurt because it would upset the convection of air through the cabinet.
 
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Old 02-03-11, 08:35 AM
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OK I am learning as I go. Originally, I was using the temp gauges that are installed at the input and output of the boiler. Recently I bought a hand held infrared thermometer. I have been reading temps by pointing the hand held at the point below the installed gauges. This is about 2" outside the boiler. I have found the installed gauges to be inaccurate by 5-10 degrees. Often the input/return is a few degrees higher than the outlet. But the hand held shows the return lower, as it should.

I just realized I have been reading the return temps incorrectly. The bypass is what I understand to be called a system bypass, meaning it is "A" in the Bell & Gossett diagram. It bypasses the system and returns hot boiler water to the boiler without going through any zones. The circ pump is on the outlet just after the pressure tank, make up water, and air separator. Therefore, by measuring the return temp at the boiler input I have NOT been correctly measuring the return temp from the zones. I've been measuring the blended temp. Seems obvious now.

I just measured the zone temps by using the infrared at the beginning of the first emitter, and then at the end of the last emitter. There is a temp drop of 20-25. Is this a more accurate way to measure temps for a zone?

Reading the B&G link they state a ball valve is not the preferred valve for the bypass. This is what my system has. It is one of the many compromises I've learned about that are in my system.

The aquastat is a Honeywell L-4080D1051 that came installed on the boiler. The Teledyne Laars Mini-Therm JVi induced draft boiler tech person said this one is set for 30 degree differential, and is not adjustable. I am assuming mine is going bad since it allows a larger spread. This is why I ordered a Honeywell L-4006A1967 to replace it. It has an adjustable differential. The tech cautioned against setting the differential to less than 20. He said it could cause short cycling.

This boiler does not come on until there is a call for heat. So the boiler can drop to well below 100 in the summer, and often below 130 on warmer winter days. Further, in the winter with the boiler operating between 160-200 I have seen it drop to 130 when several zones open at once. Particularly when the indirect water heater zone opens. It did that this morning and then slowly climbed to 200. I am guessing that once I get the new aquastat installed that it won't drop quite this far as the operating range will be higher.

I do not have a heat loss calc for the house. I never had one. The person who installed the system about 15 years ago did the job. I did not know to request a copy. I know that I requested he add more baseboard in the zone than he originally spec'd. It is a combination room that is living, dining, kitchen, entry, hallway, and partial cathedral to a loft area. So we covered all the available perimeter exterior wall space, plus another 10' along the interior stair wall. Too much of the heat escapes to the loft, bath, and bedroom upstairs, and other openings and halls. There just isn't that much wall space. It has 44' of baseboard. The total zone length is about 110' including emitters, to and from the manifold.

Thanks to Mike NJ and NJ Trooper for all the help and for the links. I am most interested in the higher output baseboards.
 

Last edited by jeweler; 02-03-11 at 08:44 AM. Reason: clarify omission
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Old 02-03-11, 03:50 PM
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FYI, If you are using one of those IR spot thermometers, it's important to get some flat black paint and paint a spot of it on each point you wish to measure. This is because different materials have different properties that will cause inaccuracy of an IR type thermometer. If all the measurement points have the same properties, you will at least be assured that you are comparing apples to apples.

Your boiler, the Mini-Therm, is of a 'copper tube heat exchanger' type, and that SYSTEM bypass is absolutely required on your system. It is there to assure that there is always the required minimum flow through the boiler, which is quite high. The Mini-therm requires that the delta T across the boiler is never more than 30. The bypass needs to be adjusted to provide this. A DT of 20 across the boiler is pretty much optimum.

Unfortunately though, that system bypass is 'robbing' flow from the system, which could be a part of your problem... or at least a contributing factor. In order to get around this, one could set up the system with a primary/secondary arrangement, add another pump that always pumps the system at full flow, while still assuring that the boiler has the required flow.

There is a temp drop of 20-25. Is this a more accurate way to measure temps for a zone?
Yes, absolutely. Paint some spots on the pipe and see if the readings change.

they state a ball valve is not the preferred valve for the bypass.
There are a few reasons for this.

A ball valve when used for throttling purposes is VERY difficult to get adjusted properly. Something in the order of 90% of the flow change is made in like the last 10% of the valve travel. EXTREMELY 'touchy'.

Ball valves have a tendency to make NOISE when throttled. Sometimes LOUD! noise of water rushing.

I also don't think it's good for the internal seals... the design is for all in, or all out.

A good quality GLOBE valve is really the best available for the job. Relatively easy to adjust, little noise. PLUG VALVES are better, but not very available these days, if you can find them at all.

Too much of the heat escapes to the loft, bath, and bedroom upstairs, and other openings and halls.
Adding higher output baseboard may not help much to correct this... it's possible that all it will do is warm the upper reaches that much more... depending on just how much convection there actually is in that space.

How much floor space in that area? What type of floor coverings? Joist area below accessible? Consider adding BTU to the area in the form of in floor radiant.

Another idea, which may or may not be feasible would be some ductwork that would pull the warm air from on high down to the bottom, and 'invert' the stratification that I'm sure exists.
 
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Old 02-03-11, 04:54 PM
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I will paint the black spots. Thus far I have been moving the spot infrared around until I get the highest reading for the location.

Looking at the installation manual, the bypass valve is specified to be a ball valve. The valve is nearly closed, handle almost perpendicular, maybe 80-85 degrees. I've never heard any noise here. I understand the regulation issue. If this one fails I'll replace with a globe valve. The Safgard #44-100 flow switch does make a small amount of noise when only one zone is open.

There is about 650 square feet in the area in question, heated by this 44' of baseboard. The upstairs loft is 400 sq ft. The upstairs bedroom and bath are another 200 sq ft. The upstairs has only electric baseboard and is always turned off, except the bath. This upstairs loft also has two large (9x7' trapezoid) windows. So this room does not get hot in the winter. With the only heat coming up from below and the windows this room is usually 5-10 degrees cooler than below. Any other rooms that are heated are keep cooler. Our system is to have this combination room (living, dining, kitchen) the only warm room (70) in the house. We leave the bedroom, bath, and hall doors open nearly all the time. I realize this heat flows into the remainder of the house. That is why I think it needs more baseboard heat. Those Smith baseboard units look like the answer, long term. The whole house has a dense, long pile carpet, except for tile and vinyl in kitchen, entry, and baths.
 
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Old 02-03-11, 05:34 PM
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Originally Posted by jeweler View Post
This boiler does not come on until there is a call for heat. So the boiler can drop to well below 100 in the summer, and often below 130 on warmer winter days. Further, in the winter with the boiler operating between 160-200 I have seen it drop to 130 when several zones open at once. Particularly when the indirect water heater zone opens. It did that this morning and then slowly climbed to 200. I am guessing that once I get the new aquastat installed that it won't drop quite this far as the operating range will be higher.
You are describing normal behavior. This is a cold start boiler. When it's off, it cools off. Indirect calls in the summer will see a fair bit of 'warm up' time. That's ok. The long firing cycle will allow it to get to an efficient burn.

The cooling off you see when several zones open is just a bunch of cold (room-temperature) water being returned to the boiler. That's normal.

The new aquastat shouldn't change any of that.


How about a ceiling fan in a strategic spot? Maybe one with a couple feet of down-rod in/near the cathedral space rather than ceiling flush mount. With that much volume, a little mixing to reduce stratification might help.

Looking at your numbers, you are heating about 1250 sf with about 24,200 BTU/hr of baseboard (44 * 550). That's about 19-20 BTU/hr/sf, so you need a bit more than that. Doing a heat loss calculation would make this less of a guessing game for sizing any new baseboard.

BTW, good job on the building envelope. Well applied exterior insulation is good for insulation and as air barrier.
 
 

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