Greetings folks... We have a lovely two-story brick house in Central Illinois, built in 1923. It has an Ideal #7 cast iron boiler, originally coal (I still have a few bushels in the cellar if anyone needs some!) and converted to natural gas at some point. It's a two-pipe steam system. The footprint of the house is 25ft x 33ft. The basement is unheated... so heated sq footage is about 1650. The attic is insulated with 6-8" of cellulose, but I don't think there's anything in the walls except plaster, lath, and 4" of brick. We've upgraded the upstairs windows with high efficiency marvin inserts, and intend to do the downstairs as soon as we can. They're original single pane w/ storms now.
As you can imagine, the bills this year have just about killed us... so I don't think I can put off the upgrade any longer. Something more efficient is going in as soon as the heating season is over... the only questions are 1) what and 2) how big.
I'm trying to do my homework in advance of talking to a bunch of contractors, to make sure we make the best decision possible. First things I've been trying to do are to ballpark the heat loss of the house, and the installed radiation. That will (hopefully) help me to decide how large of a boiler to put in, and whether to convert from steam to hot water.
I met with one contractor today, who took a look at the system and rec'd a boiler "sized the same" as what we have now. He took his figures from the plate on the gas burner, which is spec'd at min=60,000 Btu/h, max=200,000 Btu/h. So he's thinking our house needs 200,000 Btu/h.
That seemed way oversized to me. According to my math, we have no more than 120,000 btu/hour of installed radiation. (I can write up the size and style of our 9 radiators if anyone's interested in double-checking this.)
I've run through heat loss calcs with the SlantFin Hydronic Explorer software, and several other ballpark estimates, and by some gas bill shenanigans, and I can't get any estimate above 70,000 Btu/hour.
So my thought has been that we should convert the system to hot water, reducing the installed radiation to a max output of 75,000 Btu/hour.
So I guess the main questions are
1) Am I nuts to think 200,000 Btu/hour is waaaay oversized for our house?
2) Do you agree that converting to hot water would be a good idea? I know it's going to cost a little bit more to do the conversion, but I'm willing to wait 10-15 years for a payoff. We're not going anywhere -- we love the house, and they're going to bury us in the back yard.
Thanks for the help!
Its hard to say from here if your boiler is oversized or not but 200,000 does seem excessive. Staying with the steam may not be a bad idea and an afordable one. A steam boiler must be sized of of the existing radiation NOT the heat loss of the home. Chances are the pressure is way too high on your boiler. This will cause excessive gas use. my suggestion would be to find a contractor in you area who is experienced with steam heat and get his opinion. If you do convert to hot water the boiler then must be sized to the heat loss of the home NOT the radiation. However this option as you seem to know may be expensive. The existing radiators may or may not be able to be used. They may not have leaked with steam (1 or 2 psi) but they may leak with hot water (12- 18 Psi). If you go with hot water look into an outdoor reset system. This is expensive but could be very effiecient. Hot water is also a little easier to zone ( differant t-stats for differant areas of the house)
The options are endless depending on your budget. Good luck with whatever you choose. If hot air or heat pumps are not in mind check out ( http://www.heatinghelp.com) There is alot of steam and hydronic info there. this site is mainly ducted systems.
Those gas conversion burners are about 50% to 60% efficient. For steam you have to go by the net for the radiation not the input. Also you have to add 30% more btuh for the piping loss. That is if the piping is properly insulated. If it isn't insulated at all then it needs to be. Then you can deterine what size steam boiler at which efficiency you will get. The other option of converting to hot water is just plain foolish talk. Not only is the initial cost going to be rediculously high, the water parts that need servicing over the years and the labor involved is going to be a lot more than with steam.
Also keeping that large mass of water in radiators will cost you. If you convert to baseboard you may not have room for it all. And if you do you will have to make sure furniture will not block it. Then there is also the cost to install all that baseboard and related piping.
Regardless of what you do, make sure the old piping is thoroughly flushed out before the new boiler is installed.
One other comment:
If you go with hot water boiler and can't use the radiators and don't want baseboard, you can go with fan convectors. They have a lot less water in them and they are fin coils. They stand in place where the old radiators sit but are pretty expensive.
On keeping it steam....
Are you near Amboy?
I know a guy that is one of the sharpest guys I know at restoring and downsizing antique vapor systems, using all of the equipment that is in place (beyond the boiler)by orificing and resizing the boiler smaller.
That means, no renovation and repair of the finish on the building.
The things he adds are increased comfort and balance, and decreased fuel costs.
Call Dave Boilerpro Bunnell at 815 857 2339.
As said, the current rads might not be usable. You could put in some panel rads. A hot water conversion will allow you to easily heat the basement and offer you more control with zoning. It will be an expensive conversion but you'll save a great deal of fuel if you can use a smaller 70K boiler and run with cooler water temps. Modulating/condensing boilers love cooler return water temps so the extra water volume would not be a problem.
Wow, lots to respond to. Thanks guys, for taking the time.
Noel Murdough: I'm in Champaign, about two hours drive from Amboy... I'm guessing that's too far.
Foolish talk, yah I specialize in that sometimes. We won't do a conversion if it requires replacing any significant number of radiators... maybe if one or two prove unsuitable, we could get cheap replacements from the local preservation society's warehouse.
All of our existing radiators are connected at the top, and three of 'em have what look to be usable air vents. The other six would need to be drilled/tapped to put in new air vents. Most of them would need new supply valves, since the old ones leak a little steam and I can imagine would leak a lot of water. I understand there's a risk that the radiator sections will leak under the higher pressure of a hot water system. I don't know how much of a risk there really is, however. If one or two leak, we can just get salvage yard replacements. If all of them leak, it'll be no fun.
The main steam runs in the basement are insulated... The asbestos was removed years ago, and they're wrapped in about 3" of fiberglass now. The drain piping is good sized.. 1" or so at the radiators, and the same size as the supply runs when it gets near-boiler.
Is the 30% transmission loss on top of the 40-50% loss from the boiler stage (AFUE efficiency)? If so, I don't see how our system works at all, unless I'm miscalculating our installed radiation.
120,000 Btu/hour of installed radiation
*1.30 = 156,000 btu/hour output of the boiler
/0.55 = 285,000 btu/hour input to the boiler
... the burner's model plate says it maxes out at 200,000 btu/hour.
Johnsp: that's exactly what I was hoping to do. Run a smaller 70-90K condensing modulating boiler, so it runs cooler water temperatures most of the time. In central Illinois, we have about two weeks of bitter cold a year, and most of the other cold days are 30s or 40s. I'm guessing we could heat the house on much cooler water most of the time...
Given that I have to replace the boiler with something now anyway, I'm wondering whether the extra cost to switch to a high efficiency hot water system makes sense.
So many of the payoff estimates I've found for 90%+ high efficiency boilers assume you're going from a perfectly working (but 75-80% efficient) hot water boiler, to a 90% efficient boiler. So they assume you're trying to recover the whole cost of installing a new boiler over some period of time, in energy savings/cheaper gas bills.
Our situation is a little different... I'm going to be putting at least a steam boiler in... that's a given. So, making up numbers, if a steam boiler costs $6000, and a CM boiler + extra conversion expenses costs $9500, the extra efficiency of the CM boiler only has to recover $3500 relatively quickly to make sense.
Now, I understand that steam boilers are available that are 85% efficient, and CM boilers are 90-95% efficient. So 5-10% doesn't seem like much. But correct me if I'm wrong, a CM boiler makes the whole system more efficient by running lower water temperatures when it can. Somewhere I read estimates that CM versus standard hot water is about 30% more efficient, for the same AFUE. If that's the case, given our $1000 a month gas bills, I can justify the extra cost in just a few years.
Of course, this is all dependent on being able to re-use as much of the existing system as possible... if we get into installing new radiators or baseboards, it might take 100 years to pay off.
Personally, I would stick with steam. The BTU rating on that old burner meant that it could be set up to fire anywhere between 60K and 200K BTU depending on the orifice installed and the air settings.
To stay with steam, count and measure your radiators and then size the boiler accordingly. If it's two pipe, you're also going to want to replace/rework your traps to insure that they work. I would also replace the main line vents on the returns.
Avoid the guy sizing your boiler by the old burner plate. It may cost more, but definitely get yourself a company that specializes in boilers. I would skip the hot water conversion, there's too much to go wrong and you may be (unpleasantly) surprised when you pressurize it.
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Statements made by me are strictly my opinions and do not reflect the opinions of my employer. I am not authorized to make any official statements on behalf of my employer.
Any technical advice offered by me is for educational purposes only, all HVAC related repairs should only be attempted by qualified personnel.