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Help on New Boiler Size Please
My wife and I are going to install a new boiler in our home. We have a couple of quotes with very different BTU ratings. To figure out what to do I started searching the net. Mostly what I found out was that this is a complicated topic and I don't know anything and that installation is key. Seems like a lot of experts are here and I hoping for your advice.
The House and Current System
This year we moved into a new house. This house was build around 1904. It is stone and stucco. About 4500 square feet over three floors and a full basement . There are high ceilings all the way up and lots of large windows. The current boiler is 225K and was installed in the 1980s. I think the house used to be on gravity feed but we now have a pump on the return line. The house has old fashioned hot water radiators. Some really big ones. There are 4 inch pipes in the cellar part of the system. Most of the house is on one zone however there is a single large room that has its own manual thermostat. The first cold week of the year we found that the house does not get over 62 degrees F, and most of the time it got no higher than 60 degree with boiler going full blast. The water temp is set at 140 degrees. When we questioned one of the contractors on this he said it could go higher, but that we "shouldn't push this old system". The single room mentioned above does better but we do not use it much, so no help. House is in southern PA so it gets cold but rarely below zero.
The Issue
We had several contractors in to bid on a new boiler. We have two that seem reasonable, however, the proposed systems seem really different. Both contractors measured radiators and took into consideration the windows etc. This is not a price issue. Neither is cheap and I would rather pay a little more than get the wrong system. One contractor suggests two Weil-McLain ECO110Ns (95% efficient) with four system circulators for a primary/secondary system and two thermostats. So 220 total BTU I guess. The other bid is for one Lockinvar Knight 210 and one Lochinvar Knight 150 (360 BTU total?). TACO zone valve Grundfoss circulators plus outdoor sensors.
The Question
Obviously there is a big difference in capacity here. Seems like one of these is pretty far off. Anybody have an opinion? Anybody have a suggestion? What questions should I be asking? Anything else you notice? Any help appreciated.
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Harvey
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That said, you can "push" that system with higher temperatures, which will help with the heating issue. You may be pushing the boiler pretty hard, though, so that should be looked at. There are controls on the boiler for the temperature of the circulating water, and that's where I would start -- by raising that temperature. That may give you enough heat to be comfortable for enough time to do a proper job of choosing the boiler and the installer.
And a word on that: particularly on gravity systems, you aren't looking at plug and play. You need an installer who will take the time to understand the house and the system, and do it right the first time.
Such as, to go back to the beginning here, Harvey...
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
On a side note part of the issue is water temp to the rads.....maybe.
Could be air in the rads, or system.....maybe.
Could be a circulator sizing issue......maybe.
As you can see it really depends what can cause the lack of heating.
On a side note gravity systems can be really nice, and efficient IF PROPERLY done.
Has the envelope of the house been upgraded that you no of?
House is in Philadelphia so Harvey you seem pretty far away
I am probably wrong but I thought the presence of a pump meant that the house was no longer gravity feed. Is this true? All new systems suggest a pump.
We've bled the radiators a lot and they seem to be getting hot.
Outside of house is original except for storm widows on the large windows. Small windows (2 ft by 2 ft or less) do not have storms. House is reasonably tight for its age. Rear entry is unheated but we are going to add small cast iron radiator there no matter what. I doubt that insulation has been added to walls but there is some in attic.
Many thanks to all the folks who put in a good word for me!
A good question to ask your contractors is whether they are sizing the boiler based on the heat load of the house or whether they are sizing based on the amount of radiation. The proper way to do it is to size based on the heat load of the house. 100K BTU difference is to much. One, or both of them, did not do the calculations correctly. I know plenty of contractors around here size the boilers based on the radiation. Why I don't know. Maybe it's a left over product from the dead men doing steam systems?
As always, if you are getting a new high efficiency condensing boiler installed, make sure the boiler is protected from the debris in the old system. They make some nice dirt mags/seperators now to do the job.
I am curious about your current boiler? Is it a cast iron boiler? Perhaps a converted coal boiler? If it is cast iron, you need to run the system at a higher temp. If your only at 140° on the supply, your return water is likely cool enough to condense the flue gasses inside the boiler. Not only does this rust away the heat exchanger, it also creates an evaporative wall between the hot gasses and the heat exchanger, thus preventing a lot of needed BTU's from transferring into the system water in the normal fashion. I would set the system temp at 160° and see if that helps.
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Thanks for all the help I'm getting here. It is really appreciated.
You have a converted gravity. Agree with Harvey you need to get the temps back up around 180 to get the return temp up.
Bottom line you need a room by room heat loss. The btu output of the present radiators needs to be calculated to see how well they are matched to each room. If each room is over radiated that is good news for a condensing boiler. What it means is you can run lower water temps most of the heating seasons which helps up the efficiency with that type of boiler.
It would seem both contractors want to stage boilers that's good IF the heat loss dictates the need. I would favor the Lochinvar WHN Fire tube boiler over the WM Eco fire tube. The loch has a few more bells and whistles. In either case outdoor reset should be a part of the package
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Should I / Can I ask for a print out of how the estimate was calculated?
Is the burner firing the whole time?
If so is it reaching the high limit of 140 then shutting down, and relighting?
Or are you saying the boiler is running because the pump,is running?
Is the present boiler 225k input, or DOE?
To say the present boiler is to small If the high limit is still set to 140 is incorrect. Without more details on what is actually happening with the boiler.
Edit: we don't even know if the circ is the right size.
You have to ask has this always been this way. I would hardly think past owners would have settled for 62* is it..... Maybe. Usually boilers are predominantly oversized to begin with. No one ever gets a call for a heating system that heats.
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Are all radiators getting warm? All the way across the rad?
I also doubt that an underperforming boiler would have been in service for so long, so I would assume that it worked at some point. Maybe such a large circulator had been put in that the water races around unable to pick up the heat.--NBC
First, the boiler is a 1980 A. O. Smith, cooper. 225 input I think.
By going full blast what I meant was this. During cold days (10F) we can't get the house temperature above 60F no matter what the thermostat is set at. The system does seem to cycle in that the radiators get hot and then cold, then hot etc over time. I hope this clarifies things. If not I'll be happy to investigate if someone can tell me what to do.
All radiators get warm all the way across during heating. One radiator occasionally does not heat all the way across. We can fix this by bleeding it. We have had to do this maybe once a week. I don't know if this matters but, this radiator is the one highest in the house by about two feet.
I have a couple of specific questions.
We would like to try to increase the water temperature. Does anyone have an idea how this is done on this boiler? Just a rough idea would help. I'll do it myself but I want to be sure I'm not going to break something.
Nicholas B-C: My wife and I are just science nerds enough to try to do the heat loss calculations ourselves. Is the free version sufficient? Any suggestions for use?
Finally I would like to, again, express my thanks to this group for all the help.
Your boiler is cycling off the present High limit of 140 so the water is not warm enough to sufficiently heat the structure. By being at 140 on the aquastat the boiler reaches that temp the burner shuts off, and then relights at about 130.
Check system pressure on the boilers Tridictator. Should be a gauge that shows pressure, and temperature. Pressure should be 15 psi.
See how that works.
Thanks
PS I've never dreamed of 70F. We'd be all giddy with 65F
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ramermechanical.com
To learn more about this professional, click here to visit their ad in Find A Contractor.
If it does not work ( I think it will) then the heat exchanger condition would be the next step.
The unknown is how long, and or how much the boiler has been condensing with the low aquastat setting. We will talk you through that one if your game.
If it does not work then the next thing would be checking how plugged the HX is.
What have learned is that over radiation is not there. Unless we have some other unknowns like faulty aquastat, temp gauge etc. maybe 140 is not even happening. Maybe over pumping.