setting to low, not enough base, boiler too small??

tm · February 2007

It is really cold here in New York State and my system is having a hard time. The most I can get is 66 degrees. I have a small cape house only about 1400 sq.ft. I have hwbase. I have a small Biasi oil boiler. It is a B13 (67MBH). I have 3 zones downstairs, upstairs, and indirect hot water tank.

The boiler starts at 160degrees and stops at about 175degrees. It takes about 10 minutes to drop from 180 to 160 when it is very cold outside. Keep in mind this is when the domestic hw tank is satisfied and no-one is using hot water so only 2 zones are running.

So here is the big question(s): I have a feeling I can increase the high shut off to 190 will this help much?
I am also thinking I should increase the differential setting to 25 degrees. If I cant get the house above 66 degrees doesnt that seem like not enough baseboard heat? Please dont tell me the boiler is way too small.

The house is insulated but have some old single pane windows with no storms is this killing me?

John@Reliable_14 · February 2007

The boiler could be to small.......................

but without a heat loss my guess is as good as yours. Good news,yes you can turn up the hi limit(up to 200*).Most systems are designed for 180* water. Also check that all the dampers are open, baseboards are clean. I would also check into outdoor reset, so you don't waste oil/gas come warner weather.

tm · February 2007

Thanks for the reply
I turned up the high limit to 180 and increased the differential to 25 degrees - It is now cycling less often.
You say that I can increae to 200 but most systems are designed for 180 - does that mean that 185 or 190 is perfectly OK or can the higher temp cause a problem?

Brad White_9 · February 2007

I agree with John@...

A heat loss is the only reasonable way to tell. If the boiler is 80% efficient (about 54 MBH output) that works out to about 38 BTUH per SF. If the house is older but insulated, that is in range, FWIW but only as a point of reference. The fact that you have zoning can mitigate that somewhat by reducing full load at any given time...

Where I next go with this is to see what kind of radiation you have and how that is sized compared to the heat loss. If you are "short" on radiation, you can run and bounce off high limit and take a long time to reach space temperature as you are suggesting. This would also corroborate your need for hotter supply water temperatures. If that solves it, think "I need more radiation".

If you have finned baseboard or convectors, see if they are clogged with lint, pet hair, dust, etc. which can diminish output greatly. The loss is subtle over time then a cold snap makes it obvious sometimes.

While you are at this, check for things like open fireplace dampers, pet doors, mail slots, other forms of air leakage. These are sometimes easier to find when it is cold out.

Good Luck!

tm · February 2007

Thanks Brad, The Biasi specs show the boiler at 87% efficient with 58 net output for oil. All the fin tube is very new (less than one year old). I will check for air coming in. What about the hight temp? Any problem with setting at 185? Can it have any negative effect or fire hazard?

CC.Rob_2 · February 2007

how much baseboard?

Following Brad's lead, it would be useful to compare the heat loss to the total amount of baseboard installed, using that baseboard's output at ~180-190F. You could have the most optimally-sized boiler in the world (i.e., boiler matched perfectly to heat loss at design), but if there's not enough baseboard to deliver the heat, you'll never warm up.

tm · February 2007

I have about 55' on the 1st floor loop and less on the 2nd floor (it is a 1 1/2 story cape so basically the upstairs is all under roof ).
I wonder if a kickspace heater installed in the kitchen would help?

CC.Rob_2 · February 2007

measure

Now figure your heat loss, and get a better measure of the 2nd floor emitter length.

FWIW, a crude assumption is that "standard" baseboard runs about 550 BTU/hr/ft of output, or in your case on the first floor with 55 ft of element, about 30,000 BTU/hr.

Just to guess, let's say you've got 30 ft of baseboard on the second floor. That's another 16,000 BTU/hr output. Building total ~46,000 BTU/hr. How's that compared to the total heat loss?

A better way to do this is size the emitters for each room around the design water temp to satisfy the room heat loss. Whole-building averages can be deceiving (just ask the under-radiated "cold room" in my house...).

tm · February 2007

well your guess was right I have about 30' on the second floor. I'm not sure how to figure the heat loss correctly. I tried once but felt like I was doing something wrong.

CC.Rob_2 · February 2007

software

Try the slantfin software available via a link on this site, or go direct

http://www.slantfin.com/heat-loss-software-get.html

Takes a little learning, but you can get a decent first cut in a reasonable amount of time.

Mike E_2 · February 2007

If the boiler is cycling off on high limit, then the boiler is not too small and that is not causing the low inside temp. The problem is not enough baseboard to put the heat into the house.

As you said you have 55ft + 30ft = 85ft total. If your LL is 160 and HL is around 180, and your system has a 10 delta, your average water temp is 165 degrees. Output at 165 degree average temp is 510 BTU/ft, meaning you can put 43,350 BTU into the house. Your boiler is able to put in 58,000 BTU. So you have almost 15,000 BTU that can't go anywhere. By increasing the water temperature, you get more of that heat into the house. You would need an average 190 degree water to fully output the boiler's capacity. Your HL would need to be 205, LL of 185. The baseboard would put out 680 BTU/ft X 85ft = 57,800.

Now that is the band-aid. As others have said, a heat loss will show theroetically what your house needs. After seeing that, you can determine if there is too much infiltration (which can really cause huge heat loss), or not enough insulation in areas. Then you can work on reducing your heat loss and that will result in lower water temperatures, as well as possibly adding more baseboard.

And as someone else mentioned, an outdoor reset controller would be helpful as it would automatically raise and lower the water temperature to the level that is needed.

Michael

just reread your first post, you said you have single pane windows with no storms - this could possibly be a large amount of heat loss/infiltration. The easiest fix for that is the plastic film window kits. As a first step, they will show how big of a problem the windows are, and then buy some time until you can replace them with something better.

Edward A. (Ed) Carey_3 · February 2007

"All the fin tube is very new (less than one year old"

Tom,

It appears that you are trying this system for the first time in really cold weather.

Follow the instructions that others have given you re the heat loss. Good advice.

Also, a couple of questions.

If that BB is new, do you have wall to wall carpets going under the BB?

Is a carpet or ANYTHING else restricting the air flow through those baseboards?

Are all of the BB dampers on top FULLY open?

Are all BB covers on?

Ed Carey

John Ketterman · February 2007

Just to confirm the previous post, if you boiler is cycling, it is not too small! I am surprised to see posts, earlier in this thread, saying the boiler could be too small.

joel_19 · February 2007

boiler size

What the last 2 posts mean is this . if the boiler where too small it would run continuosly , the burner would never stop as it would not be able to reach the high limit setting.

You can obviously add more BTU's to the house by adding more radiation. Other factors could be not enough circulator pump limiting the output of the radiation or excessivly long pipe runs where the pipe size simply can't carry the BTU's you need.

Those last scenarios are typically found in larger Mcmansions where the boiler comes with a double O 7 and somebody puts in 10 baseboard zones plus a thousand feet of pipe.

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tm · February 2007

You guys are the best!! You all have made things very clear each in your own way. I appreciate your help more than you know. Sometimes just writing the questions down helps but all responses have given me a great deal to work with. aemeeich's response was exceptional and the following responses made it clear to me that the boiler is not too small. I have raised the high limit to 185ish and already see a huge difference. I know now that I don't have enough fin tube. I will add a kick space in the kitchen as that end of the house is coolest anyway. I also know I need to do more with the window heat loss as I expected to hear. Ed asked about rugs and dampers. We have no rugs and the dampers have been fully open.
Thanks again to all of you who take the time in your life to help others!

Jim_109 · February 2007

setting not enough boiler too small

How does one calculate the correct amount of baseboard needed?

Currently my cast iron baseboards and radiators on the first floor and slant finns on the second floor warm up the house nicely, however, my old boiler is oversized. If I upgrade to an efficient, three pass correctly sized boiler based on heat loss, will the boiler generate enough heat so I feel as comfortable as I do now?

tm · February 2007

I am still not clear on one thing. Michael said: "You would need an average 190 degree water to fully output the boiler's capacity. Your HL would need to be 205, LL of 185. The baseboard would put out 680 BTU/ft X 85ft = 57,800.
Now that is the band-aid. "

So, is there any negative effect to the boiler or parts by running at the higher average temp of 185 all winter?

Also, I have a fairly balanced system but the kitchen/family room is just a bit cooler. I will add a kickspace in there over the summer. If I have 15,000 btu available and going nowhere, what size kickspace would I install?

B. Tice · February 2007

Biasi

Tom, I have heard that Biasi installers have been running these aa high as 210 high limit on advice from the factory reps. For whatever reason. So, I'd crank it up.

Ron Schroeder · February 2007

You can leave the LL where it is and just increase the HL.

When the house is calling for heat, the LL and Differential are ignored and the HL takes over. The HL has it's own non-adjustable differential, usually factory set at 10 degrees.

The Biasi should have no problem even with a HL of 200.

By the way I would guess without even looking that the boiler is oversized. Just because over 95% of all boilers are oversized. ;-)

Mike E_2 · February 2007

I mislabeled the 185 temp as LL. What that 185 temp really is - the HL of 205 minus the HL differential of 20 degrees. As Ron pointed out above, some aquastats have fixed HL differentials of 10 degrees. I have the 7224 digital aquastat on my boiler which has an adjustable 5-20 degree HL differential (I wish it was more like 25 or 30 to help lengthen cycles)

The LL is only if you have a tankless coil, or keep the boiler warm all the time. Most current higher efficiency boilers are cold start, which do not use a LL at all. This is how mine is set up - the LL is disabled in the 7224.

So for your case, setting the HL at 205 with a HL differential of 20, would give you cut out at 205 and cut in at 185. The LL (if you use it) could be down around 150 with as big of a LL differential as possible.

The boiler won't be hurt by operating at this high of a temperature, however the efficiency will be slightly lower at higher water temperatures.

Michael

tm · February 2007

Michael,
I dont have an internal coil. I am using an indirect hot water tank for my domestic on a 3rd zone. I have an L4006A aquastat and I now have it set at 185 with a differential set at 25. The boiler is coming on at 165 and kicking out at about 195. Does this sound right? When I had it set at 175 with a diff. of 20, it never got above 175.

While I am at it Every once and a while I get air in the indirect hw zone, and then the pump wont move the water and we are without hot water until I flush it. Any way to avoid this from happening?
Thanks again for all the help, Tom

Ron Schroeder · February 2007

Is your circ. in the supply or return of the boiler? Also what size is your expansion tank? The system pressure may be droping below atmospheric when the system cools if the expansion tank is undersized or improperly charged and the makeup water is turned off.

tm · February 2007