low boiler temp

John Cockerill

He has to wire the thermostat to the circulator and maintain 145 High twmp with 10 differential. He will waste little or no fuel as the boiler will not reradiate at 145 as much as 180. He has to check to see that he ge5ts a simple thermostat that does not cycle four times an hour. He has to check the location of the thermostat. Put it in the room at the end of the loop. If he is still overheating, he can install a boiler pypass from the supply to the base of the boiler with a thermostatic valve (taco) or a good valve he can adjust to recycle enough supply water to keep boiler above 135 degrees at the temp guage. As for a boiler change out, we can make him comfortable with what he has. Someone shpould go look at this thing. We are not getting the whole story.

John Cockerill Exquisite Heat
www.Exqheat.com

Mike M.

Last fall I had a new Burnham Model 203 boiler (62,000btu input, 45,000 net IBR) installed in my 1000 sq. ft. home with baseboard heat. It replaced a 40 year old boiler that was 100,000 btu input, 65,000 net IBR. The plumber piped it exactly as in the Burnham manual (pumping away and boiler bypass). On most winter days the boiler water temp would only get up to 130-140 degrees before the thermostat stopped calling for heat. On the coldest day of the winter the water might reach 160-170. On mild days the water only reached 120. My question is this. What can I do to keep the internal boiler temperature higher? I don't want this to rust out prematurely from condensation.

The installer didn't seem to know what to do with the bypass throttle valve. He left it half closed and the boiler supply valve wide open. Toward the end of the winter I tried just the opposite: bypass wide open and supply valve half closed. That seemed to increase the boiler water temperature. Am I on the right track or do you have any other ideas to keep boiler temperature up?

By the way, this wasn't an issue with the old boiler which had the circulator on the return and no bypass. Its larger mass, higher water content, and standing pilot held the heat longer between cycles. The Burnham seems to cool off quite a bit between each cycle (about 3 an hour).

Simply Rad_2

Sounds like

You already have some sort of boiler control which adjusts the supply temps depending on the outdoor temps. The control should also have some sort of return temp sesnor to limit the cold return. Instead of a bypass I would pipe the boiler in a primary/secondary fashion and some sort of mixing devise(4 way mixing valve or injection mising) to supply the radiant panel. The installation guide SHOULD show a primary/seconday piping scheme. If, not contact the company and ask tech suuport. Look at your control book it may already have a return sesnor contact. But with out primary/secondary piping you CANNOT provide proper boiler condesation protection.
Good Luck and Happy 4th Jeffrey

J.C.A._3

Check out ...

A Taco 3-way i series mixing valve. A compact way of having the best of MOST worlds without having to repipe the entire system. Chris

hr

A boiler bypass

is not always, and in your case not, the correct way to protect against extended low return temperatures. I wish boiler manufactures would be more clear about the proper use of that piping. Or else they will continue to warranty corroded boilers

The only correct way is to monitor that return temperature at the boiler connection and have a valve, or devise, that can respond. Even a simple aquastat like Viessmann includes is better than a "dumb" bypass pipe.

If you in fact have a reset device that modulates your supply water it may have a return sensor option built in. It may in fact be connected and working whereas it drops the boiler circ off when the temperature drops too low. Is a sensor fastened near the boiler return piping?

Or you could use a Burnham Revolution which, conviently, has this protection built in, under the hood.

I'm a little surprised dropping the input BTU that much will still allow that low temperature supply to accomplish the task. Of course only a heat loss calc could help determine this.

Have improvements been made to the insulation, windows, etc or any other heat loss areas?

hot rod

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Mike M.

There is no outdoor reset or any other type of fancy control. It's strictly thermostat on, thermostat off. Heat loss calc came in at about 32,000 btu (yes, the original boiler was WAY oversized) but the plumber suggested I go one size above that "just to be safe." I looked at the Taco I series mixing valve on their web site. That may be the way to go. But I'm certainly open to further suggestions.

Mike

hr

Something's not adding

up? You said on the coldest days the boiler reaches 160- 170 and shuts down?

On mild days it shuts down at 120? This is ususlly what a reset control allows a boiler to do, run cooler temperatures on lower heat loss days. This if fine for condensing boilers but not cast iron.

You may see that temperature on start up for a period of time, but it should still reach the aquastat setting, or a temperature above condensing range, before it kicks off. You need to run that HX up to a temperature above the condensing temperature. Never want to put it to bed wet. If you watch it run for a few hours or more and it never exceeds 120, that's not good.

Ideally on a design day, a perfectly sized boiler would run non stop. And steady state running is more efficient than on off cycles. Does the boiler reach temperatures and shut down in worse case cold design days, frequently? If so, it is still oversized. If it cycles a lot on design days you may be able to derate it. With the boiler manufactures permission, of course.

Long hot burn cycles are going to be the best place to run that cast iron. Knowing there is a fudge factor in heat load calc programs it is best to size tothe load or a tad below. boilers come in a lot of BTU sizes as you look across the brands.

You may chose a mixing/ reset device to adjust the temperature to the BB, but you still need to see about 140 return temperature to that boiler after around a 10 minute run time.

If it is rusting and dripping on the burner, good chance you have flue gas condensation in the vent system. You really don't want condensation in either place.

Trade in for a modulating condensing boiler and all these issues go away and you keep more heating dollars in you pocket

Or have a control added and piping modified to protect your investment and reduce operating temperatures.

The tekmar webpage has some good explanations on how and why reset and boiler protection works for you. www.tekmar.com

hot rod

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Unknown

Sounds like.....

you also have a gross overabundance of baseboard that probably went along with the originally oversized boiler. Based on the temperatures you are stating you are seeing during the various parts of the heating season, this is what it sounds like. Just out of curiousity, how many lineal feet of element do you have in your house?

Glenn Stanton

Manager of Training

Burnham Hydronics

www.burnham.com

Mike M.

Yep, even on the coldest days last winter (-15) it didn't run for more than about 10 minutes at a time before the thermostat stopped calling for heat, then off maybe 15 minutes before the next heat call. In looking at the Burnham literature the next size down from a 203 is the 202X and the only difference I can see is that the 202X uses a smaller orifice. Glenn Stanton whaddya think?

I hope I didn't waste $3K on this installation. I'm thinking maybe I should have spent a little more and got a Vitodens.

Mike

Mike M.

It's 68 total feet of Edwards brand 3/4" copper finned tube baseboard, circa 1964.

Mike

tim smith

Baseboard output

I would estimate that at 180 degrees the baseboard you have would require about 40,000 btus. That's a pretty close matchup to your boiler I think. Good luck. Tim

John Cockerill

boiler temp agj.


There is a way to control boiler temps from the thrmostat.
check it out.

John Cockerill Exquisite Heat
www.Exqheat.com

.

Ron Schroeder

Need more info

Hi Mike,

It looks like you have excess baseboard for your heat load. A thermostatic bypass valve might be your most cost effective solution?

Is your system all one zone?
What model aquastat do you have?
What are it's settings?
Are you running natural gas or propane?
How are you heating you domestic hot water?

Ron

Mike M.

Ron,

One zone in a split loop.* The boiler does not have an aquastat, just your basic Honeywell high limit which is set at 180 (the boiler never reaches high limit). Natural gas. Separate gas water heater.

Mike

*1" copper feeds the system to the point of the split. Then it's 3/4" baseboard around the perimeter of the house back to the boiler where it's joined up again into 1" just past 2 globe type balancing valves.

Steve Ebels_3

Shoulda had a condenser

Vito or Munchkin or Ultra, OH MY!

One of them would have been perfect for your house. Alas, your obviously rowing the same boat as I am. Wherein, hindsight is always 20/20.

Let's see, a 1,000 sq ft home with an average heat loss of 25 btu/sq ft would be a load of 25,000. (There are a LOT of if's in that #) But let's just assume that's the case because it sounds like it is. If your boiler is 80% efficient that still leaves it with double the output that you need. So, you have a problem...............but there are a few solutions, some of which have been suggested. Some not.

One would be to add on to the house...............forgive me, I'm making light of your predicament. But, it would be a possible solution.

Or you could add an indirect to provide at least an intermittent heavy load.

Or you could use an indirect as a buffer tank to provide something the boiler can chew on for a while. The indirect aquastat could call on the boiler. Keep the tank running between 150 on and 170 off. Then use the coil in the indirect to supply your baseboard via another circ and thermostat relay. The boiler would see temps that it likes and a 30 gallon indirect should provide nice long run times for the boiler. Your BB temps will probably run about 10* less than the water temp in the indirect so you'd have plenty of heat from what I'm reading in your first post.

A return aquastat like Hot Rod suggested would also work. What it does is kill your circ until the boier reaches a given setpoint allowing it to get up to temp before hitting the baseboards. Think lot's of expansion noises from the BB with this approach though. Especially with old BB.

In the end the cheapest solution would be to play with your bypass until you get to the point where the boiler does get up to temp.

Your system is automatically Outdoor Resetting itself, much like many an old gravity system. I don't see where just adding a reset control would help. You have to allow that boiler to get over 140* to stay happy.

Ron Schroeder

Hi Mike,

With that much baseboard, I don't think that outdoor reset would do much good since your house would hardly ever need water above about 145 degrees, and you don't want to run the boiler much below that or you will get condensation.

The absolute cheapest way to set up your system would be to change it to stay hot all the time with the high limit controling the boiler temperature and the thermostat only controling the circ. If that high limit has adjustable differential, I would set it for 15 degrees and the temperature dial to 145. The burner would then fire until the boiler reaches 145 degrees and then the burner will go off until the boiler drops to the limit controls setting minus the differential or 130 degrees (which is the lowest you boiler should go if fired with natural gas). You would wire the thermostat thru the switching relay to the circ. only instead of both the circ. and the burner and just turn the whole thing off when it is not the heating season.

What is the exact model of your high limit (single aquastat)?

Considering the (way oversized) amount of baseboard and the size of your house, I don't think any fancy controls would really save you much if any fuel or give you more comfort unless you went to multiple zones (unless your heat loss is a lot more than I am guessing).

If you find the house doesn't stay warm enough on the coldest days, just bump up the aquastat setting a little. Remember that the aquastat setting minus the differential must be equal to or greater than 130.

Personally, I would also add a (preferably manually reset) auxiliary safety high limit set at 190 degrees.

Ron

Mike M.

Ron,

The high limit is a Honeywell L4080D-1036.

Mike

Ron Schroeder

Unfortunatly, that aquastat has a fixed differential of 15 degrees but you could still wire it up as I have mentioned to keep your boiler warm all of the time and prevent condensation.

Ron

John Cockerill

Exquisite heat

Take another look. What about the variation in weather from noon to 4am That is about 20 degrees, with all different factors of wind, sunlight, temperature. Wouldn't it be simpler to control the boiler temperature with the thermostat. What if your not home. It would sure be better if Honeywell made a user friendly aquastat as user friendly as a clothes washer. Besides the aquastat is not a true indicator of the boiler side temperature for consensation. By the time the boiler cools down from the last firing the exhaust gases will have gone up the flue. What is the temperature of the fire. Condensation? If condensation does not form on the wall of your basement at 70 degrees, how can condensation form on the wall of your furnace at 130. Hot air rizes, unless you are one of those with a closing damper trapping the exhaust gasses in the chiminey.
John Cockerill Exquisite Heat
www.Exqheat.com

Ron Schroeder

Hi John,

It's all a matter of dewpoint. The air in the basement has a dewpoint of less than 70 degrees so there would be no condensation but the dewpoint of the products of combustion is much higher since one of the products is H2O. The dewpoint will also depend on the percentage of excess air in the combustion process but with natural gas, it is typically around 130 degrees and with oil it is around 113 degrees.

So to prevent corrosion of the inside of the boiler, it needs to get above that temperature long enough to evaporate off the condensation on each burn cycle.

Ron

bob_34

how about the anticipator?

are we working with an old thermostat with a mismatched heat anticipator setting causing short cycling here? bob.

Mitch_4

best guess is

that the boiler is operating perfectly, but is so WAY oversized, it never runs long enoug to reach 180° except on the coldest days.

Was a heat loss done? for 1000 sq.ft. your boiler is probably 2x bigger if not 3 that required, While you have the baseboard to support it, you probably don't need it either.

The combination baseboard length and sixe of the boiler is too close to be happenstance, and I would say your installer sized it by measuring how many you feet you had, and picked a boiler to match it.

a smaller boiler to me is the only solution. Get a proper heat loss, and contact the manufacturer to see if they have a de rate kit.

Good luck

Mitch

Mike M.

It's a brand new Honeywell Focus Pro 5000 digital thermostat, no anticipator, set to 3 cycles per hour.

Mike

John Cockerill

thermostat location

It the thermostat at the beginning of the loop . It may be satisfied with the hot water direct from the boiler.

John Cockerill Exquisite Heat
www.Exqheat.com

John Cockerill

dew point


If the boiler does not have the damper closing after fire ( condensate heaven) the draft of hot air will suck the condensate up the chiminey. by the time the boiler wall cools down to 130 the exhaust will be gone. So you will be ableto go lower before condensate. It is my opinion that the condensate and low boler fire side temperatures is over exadurated. I would agree to run temps lower than 130 at the aquastat can have risk. With the low delta T ( difference between supply and return water) achieved with high circulation rates the cooling process is less likely to create boiler fire side condensation. If you have high aquastat settings, low circulation run times and cold return water the condensation risk is higher.
John Cockerill Exquisite Heat
www.Exqheat.com

Ron Schroeder

Hi John,

I think Mikes problem is not condensation on cool down rather a problem that in most winter days, as he states, it never gets up above 130-140 degrees DURRING the burn so he has condensation risk even before it cools down after the burn. I have seen a lot of rotted out boilers that are hooked up to over sized hot water coils in air handlers that never get hot enough too.

Ron

John Cockerill

3 cycles per hour??

For hot water heat? How long does the circulator run. Why start up the boiler for a small house three times per hour. How long does the boiler fire each cycle? Re read the thermostat instructions for hot water. Are all the radiators the same temp throughout the house? If not you need longer circulation. If they are too hot turn aquastat to 145. Set differential to 15 degrees. You may need a bypass pipe from supply to base of return with adjustable valve, to keep the heat in the boiler at 145. You may wish to ad a mixing valve for mixing return water to supply water to cool down radiator water. Where do you live?

John Cockerill Exquisite Heat
www.Exqheat.com

Trevor Baptista

Primary/Secondary Piping

Is the attached schedule a good primary/secondary scheme?

RoosterBoy

Trevor that is a condensing boiler with series circuits

Trevor Baptista

So it should be fine then...

Trevor Baptista

So it should be fine then...