Typical Boiler Circ. Time On/Off

Joe G.

First-time home owner - First winter!

My gas bill is ridiculously high! $350 for the previous month, and the true cold of winter hasn't really set in yet!

In my 100yr old two-story brick duplex with a hot-water radiator system, my gas boiler is heating/circulating two times as long as it is idle. (8-9min on, 4-5min off).

Recently, it has been in the 20's and 30's outside.

The boiler is in the uninsulated basement, and my ~1200sqft apartment is on the second floor. Each floor has its own boiler system.

Above me is an unheated attic and below me is a (currently) unheated apartment, which is currently at a temp of 55-60F. The attic has mineral wool insulation and is about 6in deep. My walls are plaster, but probably uninsulated. I have 17 windows in the apartment, some of which are plastic covered now. I also have minimally insulated hardwood floors.

I keep the thermostat at about 69-70F, and I have the boiler high temp at 200. I also set the resistor in the thermostat according to the engineering drawings for my particular boiler (0.4)

Also, there are a few radiators that have been removed. I currently have six radiators, but as far as i can see, there used to be three more. previous owners must have removed them. I'm thinking that this could be part of the problem - not enough heat for the amount of space in the apartment.

I am about to start major insulation projects for the pipes, the attic, the rest of the windows, doors, baseboards, elec outlets, and anything I can think of.

Is there a typical or ballpark value for the boiler on/off time?

Any other ideas for me? I would appreciate any help I could get.

Help!

Joe

Big Ed

Cycle

The on off cycle depends on constant and changing factors.Idealy the system will run constant ,maintain desired room temperature on the coldest day of the year. To determine if your short somewhere a heat loss calulation needs to be done on the dwelling first.Check the needed btus to the out put of the system.A good local heating pro can proform the calulations...

p.s. All the work your planning would save you fuel...

Joe G.

I used the Slant/Fin Heat Loss program and got about 79,000 BTU for my apartment. The only thing I wasn't sure about was the "Cold Partition" value. What is that? IFor that, Ijust used the same numbers as I did for the outsde wall values.

For the Boiler BTU/efficiency, which number should I be looking for? Where could I find this? Or, is it a function of the entire system?

So, to find out is there is a short, I need find the Heat Loss (79,000) and then the input. Then, is the difference the lost energy? If there is a big difference between the two, does that mean that there is some other source of heat loss?

Thanks,
Joe

Uni R

Apt Heat

I'd try and find out if the lower apartment is even using any energy to maintain itself at 55. It could be that it gets enough heat just through your floor and from the boiler being underneath it. If so, I'd try and get that better balanced by your landlord. Did you factor in the floor losses in the heat loss calculations?

I think a cold partition wall is for situations where you have a joined garage. The interior wall that shares with the garage is typically insulated as well as an outside wall but has less heat loss because the closed garage isn't exposed to wind.

R. Kalia_8

The circ on/off time is not a useful standard measure of anything (properly set up systems should run 100% of the time), and how much you are paying is not a very useful figure either because the cost of gas varies.

How many therms did you use in the billing cycle (this is on your gas bill)? Hw many degree-days were there in the cycle (this could be on your gas bill)? With these numbers people couldn tell you if your gas usage is in the ballpark or not.

PS The "unheated" apartment is actually using a good bit of heat, through your floor, which is why it's so much warmer than the outside temperature. So in effect you have a 2400 sq ft building.

Yes, the removal of radiators could be part of the problem, and could mean that the boiler (however big it is) will not be able to heat the house in the coldest weather, because the radiator capacity is a bottleneck---the circ can't run more than 100% of the time. But while removing radiators will cause the boiler to run longer, it will not cause the gas usage to be higher.

Joe G.

OK. I found the boiler info.
105,000 BTUh input
88,000 BTUh output

With the corrected cold partition info, my house has a heat loss of:
76,000BTUh

It seems the that boiler is sized correctly, because pros installed it. I just wanted to check.

Yes, you are probably right about the basement boiler and the floor loss from my apartment heating the apartment below.

I will look up the "Therm" and "degree-day" info on the gas bill.

I am the landlord (only for about three months, though). There isn't much I can cheaply do with the floor insulation though - original hardwood floors and plaster ceilings. Tenants will be moving in in a month or so, which will hopefully turn the tide my way, I hope.


Also, I am surprised to hear that a properly designed boiler should run 100% of the time. Is that because it is more efficient to maintain a set temperature that to raise the temperature by a few degrees?

This seems a little contradictory to me because having the boiler run all the time seems like it would be using a lot of gas. I understand the BTU (energy conservation) issue, but I don't quite get how it uses less gas if the boiler's running.

Learning a lot here. I appreciate the help.

Thanks,
Joe

R. Kalia_8

System running all the time doesn't mean boiler running all the time, even in your current system. When the water heats to the set point, the flame goes off, just like your oven goes on and off the hold the cooking temp.

A modern system will vary the water temperature based on outdoor temperature, such that the water circulates all the time to heat the house. The boiler burners will still go on and off to hold that water temp. It's called "outdoor reset".

Anyway, I would guess that the radiators were removed when people lived downstairs and so there was enough heat upstairs. Now that the downstairs boiler is not running, and the whole house is heated from upstairs, there may not be enough radiators upstairs.

Joe G.

OK.. I understand that much better now. My boiler IS always running then.

However, it seems like my circulator is only running when the boiler is fired. The only noise I hear is the faint sound of the pilot when the burners aren't on.

As far as I can tell, when the system is signaled by my thermostat, the burners fire, the exhaust fan kicks on, and the ciculator runs. The thermostat's electical leads look like they are shared between the circ and the exhaust fan.

That would be an incorrect set-up, if that's the case, right?

I'll have to check more closely on that.

Thanks.

Joe

R. Kalia_8

No, your boiler is not always running.

The circulator runs continuously when there is a call for heat from the thermostat. The boiler also starts when the circulator starts, but it does not run all the time---it goes on and off as needed to keep the water at the set temperature. When the call for heat from the thermostat stops, everything stops.

It's a chain of events: the boiler gnerates the heat, the water carries the heat; the radiators release the heat. If there aren't enough radiators, they can't release the heat fast enough, so there's a bottleneck, so the water has to circulate longer (circs run longer). But the boiler doesn't run longer, it idles a lot because it can generate heat faster than the radiators can release the heat.

Mike T., Swampeast MO

You say the system is heating/circulating for about 9 minutes with 4-5 minute "off" intervals.

Is the boiler firing for the entire heating/circulating interval?

BTW, natural gas is priced insanely this season and you likely have the worst possible situation with the downstairs unoccupied, [probably] solid brick walls without insulation, [sounds like] an abundance of leaky windows without storms, and removed radiators.

Joe G.

I'm 99.9% sure that the burners are firing the whole time when the circ is running. I have never seen it do otherwise. I have sat in the basement watching it, too.

In answer to your question, the circ and burners both run for 8-9 minutes, and nothing for about 4-5 minutes.

I don't think I have that outdoor reset you mentioned. Is that something that shold be added?

Also, the highest boiler water temp that I have seen is about 130-140. I have the high limit set at 190, but it's never come close to that.

Based on everythign else, does it seem as though the boiler is running fairly normal?

I still need to check the therms from the gas bill.