Homeowner with boiler problem

John_69

So here’s the story…

3000 sf house in northeast Pennsylvania. I had a 350k btu natural gas hot water boiler that was about 60 years old with cast iron radiators on 2 of the 3 floors. Heat was relatively comfortable. The boiler had problems with the safety circuit, was inefficient and I stayed up at night worrying whether or not it would leave us stranded without heat.

We replaced the boiler with a Burnham 198K btu boiler. Removed some of the radiators on the first floor and replaced with ductwork (zone 1). Some of the first floor (zone 2) and all of the second floor (zone 3) still has radiators.

We installed a Bryant variable speed air handler (slightly oversized) with a hot water coil to make hot air.

Unfortunately, we only say a 1% decrease in fuel usage. HVAC guy says “Gee, I guess the old boiler was not as inefficient as we all thought”. Not sure what to do about this problem yet.

The problem that we have been having is that the first floor is cold. We started to run the ahu fan 24 hours a day to help but that seemed to make it worse. The HVAC tech originally set the aquastat at 140 degrees. This seems a bit low to me but I figured that we would try it. Last week I bumped it up to 160 degrees hoping to get more heat gain across the coil if the water temp is hotter.

Lat night the t-stat was set for 68 for first floor radiators and 72 for first floor air handler. I got up this morning to 68 in the area served by the air handler. Boiler was running and rads were hot. Air handler was not running. (maybe on delay). I checked the boiler and it shut off at 170. Should that limit be set hotter? Even so with the aquastat at 160 shouldn’t the ahu have been running?

Any thoughts?

I have a call into the hvac company but I am beginning to trust you all more than them.

Sorry for such a long post.

Mitch_4

If your 1st floor

is cold, I would say that you AH is running at too high a speed, The air flow must be slow enough to actually pick up the heat.

I would measure the incomming and outgoing water temperatures and chack against the owners manual (they should state the output at a given temp with a specific delta T)

.I would also check the temperature rise of the air through the AH there should be a chart for that as well. Remember that a 20° difference in water temp does NOT equate to a 20° rise in air temp.

If neccessary, slow the fan down.

As to the efficiency.. you should be LIGHTYEARS ahead. something isn't jiving with this.

Hope this helps.Good luck.

Mitch

John_69

The ahu is running at about 700cfm. The unit is slightly oversized for a future addition.

I haven't check discharge air temp yet.

What else can I check for the effeciency? We checked gas pressure and it is in line.

Mitch_4

what is

your boiler water temp set to? The AH will have information as to what water temp you need to produce "X" BTU/hr. This needs to be checked against your first floor heat loss.

If at say 130° boiler water, the AH will emit 20,000 btu/hr, and the heat loss is 30,000. It will always feel cold, the boiler will run more than required because the AH is calling for heat, and it will use a ton of fuel trying to keep up with your heat loss.

M

John_69

Mitch,

That was my thought. The Boiler high limit is set at 170. I thought that this was too low.

I just talked the the HVAC guy. He agreed that the boiler water is too low.

The aquastat for the ahu was set at 140 and last week i bumped it to 160. The hvac guy is not sure but thinks that they may have wired the ahu aquastat to shut the ahu down is the water temp is below the aquastat temp. so by raising the aquastat temp to 160, I was working the other way. They are going to check with the tech who installed it.

But you may be onto something with the lower boiler water temp and excessive fuel consumption. The boiler is rated at about 83% and has been measured at 79% effeciency. This could explain why I have only seen a 1% savings.

Mitch_4

even then

your old boiler would be way less than 79. Did you, when comparing consumption, do $2$ vs last year? or was it calculated against degree days used?

unless your conditins are exactly the same, $2$ is not the way to check savings.

Mitch

hr

Still sounds like a lot

of boiler for 3000 square feet? 198,000 would be about 168,000 output or about 56 BTU/ square foot of home. That is a BIG number!

Was a heatloss calc done to size the replacment equipment? Could be a short cycling boiler consuming a lot of fuel?

Did the AH get installed with insulated duct work, if it runs through unheated spaces?

A heatloss calc is always needed when replacing old equipment, especially if upgrades have been made to the building efficiency, windows, insulation, etc. As such the current load could be a lot less than before improvements were made. Just some thoughts.

hot rod

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John_69

The heat loss calcs were done and ranged from 99k-200k depending on the different contractors that I talked to. We are planning on an small addition in a few years so we wanted to keep that in mind. The boiler that we took out was rated at 350k.

I haven't really observed any short cycling.

The ductwork was installed in the basement. There is on rad down there that helps out a bit but it is still cold. All the ductwork has been well insulated.

In calculating the savings, I did not look at the degrees days. The average temp is provided by the utility on the bill. The average daily temp was 33 degree for both years. I was also using the ccf of gas rather than just the $ value of the bill (of course gas has gone up). While this may not be 100% accurate, I figured that it would get me into the ballparck of savings.

The house is 135 years old. There have been vinyl replacement windows added so there is no draft. We have begun our renovations and are installing better windows and insulating exterior walls. That being said, the renovations that we have completed this year did not have any effect on the tightness of the house (it was a non-productive year.) So our comparrison to last year should be pretty good.

Mitch_4

so you

had a lot of variation na what I assume was a shell heat loss.

Because you were retro fitting a new (hydroair) system for some parts, was the heat loss broken down to determine what the loss was for the new system? A room by room should have been done to determine the requirements for the ducting design to get proper air distribution where you need it. and to properly size the air handler.

If you did not get this done, everything you have is based on GUESS WORK!, it may be an educated guess, but its still guessing. Also sounds like they did a like for like boiler choice, albeit they at least did it on output. If your old beast was 350,000 @50%, you had 175,000 output. your new one is 168,000 out as Hot Rod pointed out.

Get the free heat loss program available here and play with it, and see what you need. You know the construction of the house, and you will be able to do a room by room, then total up the new parts to see if the AH is sized right.

Mitch

Big Ed

Good Man

Sounds like a lot of guess work . Look up Mike Kraft . He is the man to call in NE Pa

John_69

So where do I find Mike Kraft? He is not listed in hte find a professional.

John_69

So where do I find Mike Kraft? He is not listed in the find a professional.

Unknown

Use the search feature

Look for the word "cheese"

Noel







I'm serious.

Jeff Lawrence_24

Try here

You'll have to Copy and Paste


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