Normal cycle time/duty cycle?

Jay_17

I have been observing the new boiler we had installed in our house (hot water baseboard all new). This is a remodel from older steam, this boiler handles the first floor, about 1100 square feet. As the temp got down to around 0F recently I realized that the system was struggling, the house is not fully sealed or insulated yet, and it was pretty much running 100% to keep up. I timed the actual burner on time and found it is around 7 minutes on and 7 off, so a 50% duty. I upped the water temp a bit and it shifted to about 8 on and 6 off.
Is this a normal duty cycle, It seems to me that I have a little too much furnace for my radiation, but I do have one kickspace heater that is not yet wired, so it will probably help in that respect. This doesn't strike me as a short cycle, but I really don't know.. What else should I check?
Jay

Bill Nye_2

Struggling?

I don't understand what you mean? Is it heating the house? If it was not capable it would be running 24hrs non-stop. It must be cycling off of high limit which is quite normal.

The boiler is only part of the equation. All bets are off until you seal up the house

Mad Dog

Dude! You've gotta get the house insulated before

you start "playing" around. Are you the installer or the homeowner or both? You really shouldn't be playing around if you are not qualified. Don't wanna see you get hurt or void the warranty. Mad Dog

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oil-2-4-6-gas

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if your boiler is not shutting off at all the burner is constantly on then you have a problem --you say its unfinished--well given the outdoor temp the past few days -it should run a lot -when its all finished it will of course be less --my boiler installed new this year --Buderus--is puuring along as it should it is designed for max load at this temperature +20% ---depending on the control strategy and system --you should be running a lot this is the weather your system is designed for. if this is a brand new install still under warranty -any issues should be directed to the installer you should not touch anything.period ---

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Yes, you are right, your boiler is oversized. It is very common for installers to oversize boilers, and then warn their customers not to "play around" with the boiler so they won't find out.

But this does not mean you have a problem with too little radiation. Is 0F the design temperature for your area? If not, and the thermostat is calling for heat 24 hrs a day at 0F, then when it goes to -5 or -10, the system won't be able to keep up at that water temperature. The solution is simple, and you've already found it: increase the water temperature. Your boiler is certainly capable of producing the hotter water without breaking a sweat.

Jay_17

clarification

Ok, let me clarify, at 0F outside, thermostat at 65 and the temp was only getting to 61, so the system is running max capacity. The circulator is on all the time but the burner is on for 7 min off for 7 min.
I checked the boiler set point and found that it was under 170, I know it can run up to 200 at least, so I bumped it up knowing that would get me more heat transfer from the radiators.
I understand that I need to insulate/seal, but if I could get that all done after work one evening I would have done it 6 months ago.... We do have new windows and most of the walls filled with fiberglass, tyveked, foamed and sided, but the winter caught up.
I don't know what the design temp is or should be, but I know my requirement is that it maintain 65 in any likely temp, we rarely see less than -10 really , so there you go.
So the system should run 100% duty cycle at this temp I gather, that is all I needed to know
Jay

Wethead7

Design temp

The design temp is the average temp of the coldest day you should expect to see on a given year. Abnormally low temps that happen everly ten years or so are not the correct design temps. I E drops down to -10 tonight up to 10-15 in the afernoon. First yime it was this cold in years, is way below design temp day. 10 below are you in Canada or a boarder state?? 10 below design would be temp dropping to 20 below or lower several times a year. That would also include warming up to near Zero on those days.

I think you way low with your design number.

Mike

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Hmm...more than one contractor told me that here in the Chicago area they use a design temperature of -10F.

Now it goes below -20F only once in 10 years or so, in fact we are planting zone 5b which means plants only need to be hardy to -15F. Most years we don't hit -15F at all.

So by your definition -10F is too low a design temperature. Who officially calculates design temperatures for various areas? Is it on the web somewhere? Wht is the design temp for the Chicago area? Thanks for the help,

Wethead7

design

The tenp is the lowest average tempature for the coldest day of the year. We then add last 10 years or more and devide by the number of years added. I E Coldest day was low of -10 warmed up to 10. Then that year is 0. Add the last decade. 0+{-1}+3+5+0+{-6}+{-3}+{-4}+10+5=10 the devide by 10 = 1 That would be your design temp. The heat loss is based on this. The heat loss figure does not account for other heat gains [cooking, bathing, other appliances]. The loss of a couple of degrees over a long term under design temp is not usual a problem. We tend to design tems that way to low from people not trained in the proper way to preform heatloss calac's . The weather service provides them, but most of the time they are incorrect. They do not use the average daily temp or average several years. The local heating and or cooling company can provide you with this information.