I’ve been tasked with replacing the old boiler in my in-law’s house, a 1920’s house that has cast iron radiators and questionable insulation. The current boiler is a 1960’s oil fired sears converted to nat gas some years ago.
What should I replace it with? I really like the idea of condensing boilers like the munchkin but I’m not sure if the modulating boiler works well with the old radiators. The established (old) contractors stay with the old tech around here (duluth,mn).
5 years ago we replaced our own boiler with a weil-mclain 80% efficiency because our heating contractor told us that was best. I can’t help thinking we should have gone for a higher efficiency unit, the prices aren’t that far apart.
Replies
You might want to post this over at http://www.heatinghelp.com
They specialize in hot water and steam heating systems.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
There way too many missing details to answer.
Is this a steam or a hot water system? One pipe system or two? How is it zoned?
What is the input of the boiler? What is the out put of the boiler?
What is the house's heating load requirement? What are the windows like? How much is the existing boiler over sized? Ever hear of EDR?
Whether or not the new boiler modulates will not affect the ability to heat using tihe old radiators (assuming this is NOT a steam system), but the temperature of the supply water will. What temp is supplied now?
The preices between a Weil-McLain cast iron (i.e. 80%) and a W-M modulating condensing boiler is not that far apart ? Not when I sold Weil-McClain boilers. The Ultra is an awesome machine. More expensive than a Munchkin, but way better, IMO.
<i>Is this a steam or a hot water system? One pipe system or two? How is it zoned? What is the input of the boiler? What is the out put of the boiler?What is the house's heating load requirement? What are the windows like? How much is the existing boiler over sized? Ever hear of EDR?</i>Thats a lot of questions. The system is hot water, two pipe single zoned. As to input, currently natural gas and DW to top up the system. The old boiler is a converted oil unit with the gas burner unlabled as to size. but sufficient for the last 40 or so years. I wasn't asking for a heat calc on the house or for boiler sizing. The house is OLD, leaky, and in northern minnesota. I hope a good contractor will size the system. Equivalent Direct Radiation? Yes, I've heard of it.My question was just about con-mod boilers. Can you take full advantage of the efficiency with the old cast iron radiators in an old house or will the you need so much more surface area to take advantage of the lower temperature? I think it's about 180 degrees now.The cost differential between the W-M and the Munchkin at the time was small compared to the heating costs in the great white north. Thanks for the input!I'm doing some research for my father-in-law, you answered a question about GSHP for me a couple weeks ago (BTU vs Ton) and I thank you. The house needs lots of updating (windows, insulation, paint, plumbing of both the water and walls, and a heat source) and so a heat calc for today isn't going to work tomorrow and he'll have an over-sized system. Thanks again, Ted
You're from Duluth huh? Me too. I have seen plenty of modulating boilers around here, though I'm not sure of the answer to your specific question. There are plumbers around who put them in. I do think they are quite a bit more money in the end. I would call the heating design guy at the plumbing wholesaler of your choice. My guess, just a guess, is that the modulating boiler is less of an advantage when coupled with old cast iron radiators.
The answer to your question concerning can take "full" advantage of the mod/con efficiency with old cast iran radiators is: no.
However, mod/con boilers, even when operating in the non-condensing ranges (i.e. with return water temperatures above 140 degF) still have AFUE values above 90% and considering that what you describe probably has an AFUE in the 60's, and given the location, ever increasing cost of petroleum products, etc., etc., a mod/con will pay for itself before the warranty expires.
As much as I can recall, a W-M Ultra (one of my favorite ng fired domestic boilers) was about 50 to 60% more costly the "gold". Not a fan of muchkins, though they are "cheaper" than the competition.
One thing to keep in mind is that the existing unit is probably no more than 60% efficient. Even if you replace it with only an 80% unit you'll save about 25% on heating costs.
Too much sanity may be madness. And maddest of all, to see life as it is and not as it should be! --Miguel de Cervantes
You won't be running 180 F water to the rads all year long, even in Minnesota. When you run lower water temperatures, you will save even more with a mod con boiler than with a cast iron non-condensing mid efficiency unit. And you'll save quite a bit relative to what you've got even at 180 F.
As to the Munchkin- so far, so good on my place, where the old rads are basically one zone and the addition is heated with in-floor radiant loops taken off the return line from the rads.
One really nice thing about rads: they respond FAST, so you can still do an evening temperature set-back and not need to wait forever for temperatures to recover in the morning (the mod con helps with that too- gives you full output when you need it without the worry of short-cycling when you're back up at temp). I've always found it more comfortable to sleep in cooler conditions. And under most circumstances it DOES save money to do so.
To All, thanks for the advice, the actual experience is good to hear. If I understand it right, the modulating boiler will perform at lower levels efficiently and avoid the short cycling problem of an over sized unit. So as the insulation, windows, etc are replaced the oversized boiler will be okay?
NRTRob will no doubt chime in shortly to give a more knowledgeable opinion than I can offer, but here's a few more cents worth from me. You're right that mod con is the way to go if you're planning to reduce the heat demand significantly by removation over time. But get an outdoor reset controller so the water temperature will decrease automatically as it warms up outside. Otherwise, if you don't adjust the recirc water temperature setpoint on the boiler based on the heat loss rate from teh house (ie. how cold it is outside), you'll end up with the same basic thing that you had with the old boiler: a very high water temperature setpoint for the very coldest day, such that on warmer days the rads get too hot and over-shoot. That leads to both discomfort and short-cycling of the boiler. Some benefit of the modulating function would be wasted if you operate this way.
I was too dumb (and too cheap) to go this route, so now I have to act as the reset controller myself. Fortunately it takes about 10 seconds on the Munchkin to set a new temperature setpoint. I find I only have to adjust it about once a month during the heating season to keep things comfortable and reasonably efficient, so I don't mind too much. But the system would have been more efficient and easier for my wife to use if I'd sprung for the auto outdoor reset controller. Unfortunately, the downside of the automatic outdoor reset controller is that it works best with a steady temperature setpoint in the house- no night-time setback which we like.
Weil McLain Ultra 3 series is just out I think - latest and greatest. Outdoor air reset kits available.
Jeff