replacing old radiators with modern ones
At this point, I have used several engineering textbooks on the topic and consulted with a number of engineers and plumbers, including you. There are a lot of reasons why systems are built less efficiently, and a lot has to do with cost and time to figure things out to design a robust and efficient system and then properly execute that design, and I can’t possibly cover it all here. There are definitely differences of opinion, and ideas that are good in theory don’t work that well in the field. These comment are a few of my general thoughts based on my own research, interviews, and experimentation in a brownstone. This is from the perspective of an owner, things like callback risk weren’t a primary design concern. But that said, I do actually recommend using an engineer to draw plans for the system and schedule the equipment. But that said, it may be too expensive to be practical. But the drawings make it much less likely a design or construction error will occur that reduces the performance.
hkapstein
in General Discussion 4 years and 4 months ago
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christinamove | 4 years and 4 months ago
Ooh. Ohh @Master Plvmber or @Urbandad. Do you (or anyone) have a good recommendation to replace baseboard (hydronic) heaters. We have probably the cheapest there are (from our flip). I’d like to upgrade to better efficiency and aesthetic. I’d been looking at the Runtals and the Hudson Reeds. It’s difficult to really get the clear data of their efficiency. Especially vis a vis what we already have (which i hate the way they look and the difficulties of cleaning them a couple times a year; fins and cheap covers at back breaking height). I’m trying to be smart about what we fix and don’t fix with the house (ie: see the return in efficiencies within our lifetime).
christinamove | 4 years and 4 months ago
Just to add (and be clear) it’s closed loop (water). Operating temps are set to 180. Getting radiators that run at lower temperatures would be amazing. But, can I replace them one by one? Or, would they all need to be replaced at once? Much thanks.
Master Plvmber | 4 years and 4 months ago
@christinamove First, the concept of efficiency doesn’t apply to radiators. All radiators are 100% “efficient” meaning that every single BTU of heat that is put into them is released to the room every time. You are right to question whether or not radiator types can be mixed since all materials of their construction both absorb and release heat at different rates at different water/steam temperatures. The answer is: you’ve got to do some math and figure out what you can get away with but generally speaking, mixing radiator types doesn’t work well. The quick answer to your question of what to replace baseboard heaters with is, in my opinion, is the Runtal UF series.
I wonder if Brownstoners would be into doing a Zoom call to answer some of these questions since they tend to lead to some in-depth conversations.
christinamove | 4 years and 4 months ago
Thanks @Master Plvmber I, for one, have tons of questions about my heating system. Mostly to do with how can I make it run more efficiently. And, where the best places to make capital investments into it and make it run using less natural gas.
christinamove | 4 years and 4 months ago
I know part of that answer is insulation, windows and overall air tightening. Which we are making progress with. But, I also wonder about the heating system itself. And, if there is equipment beyond what I already utilize to help it burn less gas for the same output. I have a whole theory about putting in a solar heated tempering tank to “heat assist” the gas furnace. I go back and forth with my logic and how to make it work/if it would work. Or, is an outdoor thermostat worth setting up? etc.
hkapstein | 4 years and 4 months ago
Hey Christina! I read an engineering textbook about hyronic heating design and talked to a number of plumbers and engineers before I did my project. Here are some takeaways.
1. Natural gas is the fuel source we are using for most systems in NYC. When you do your AC system, I’d strongly recommend you size it for a heat pump. I believe NY State wants to phase out natural gas and move towards renewables, and the heat pumps are now very efficient. I think they might be more efficient than natural gas when the temperature is over 40 degrees, and that’s a lot of the heating season here, and the balance will likely move toward electric heat pumps as energy policy evolves. (this is not based on engineers or textbooks, but just my opinion)
2. To maximum a natural gas hot water system, which is likely what you have if you have baseboard(and btw that means you have a boiler, not a furnace), you want to operate the system at as low a temperature as possible. There are several reasons why. If you have a condensing boiler, water will condense in the flu below about 130 degrees or so , and the more condensing, the more heat is retained. Also heating water to a higher temperatue will result in more jacket losses and piping losses in unconditioned spaces. But, the lower the temperature of the water, the less heat the radiators will put out. So the system will be more fuel efficient if the radiators are:
a) oversized for the space(more radiators that can meet the heating without their full output at 180 degrees on most days). More radiators will make your system more efficient, but they cost money and takeoff space, so you have to assess that tradeoff.
b) designed to output heat at lower water temps(probably low mass, like steel column radiators, panel rads, or convectors are better at this than heavy cast iron, but also the boiler should be low mass if this is the case).
3. Another issue to consider is setback recovery. A low mass system can become hot very fast, but a high mass system can take a while to get the radiators hot. With a smart thermostat, you can keep the house at a lower temperature at night, or while you’re out and have it heat back up quickly when you trigger a schedule or motion sensor. Under most conditions, the heat pump can probably help you recover temp even faster. So depending on your personal behavior, you can save fuel by optimizing this. I determined that it’s quite comfortable to sleep at temps as low as 62 degrees, whih saves a lot of fuel, but I wouldn’t do that while I had an infant.
4. TRVs or zones can help you save fuel and stay comfortable. A TRV(thermostatic radiator valve) will shut down radiators that are making the room hotter than the setpoint, and are easy to install without repiping the system which zone valves would require. A commmon waste of fuel is to have some rooms hotter than necessary while others are too cold resulting in cranking up the thermostat. There’s a lot to say about TRVs, but if you want to understand them, you can easily google it up.
5. You mention replacing baseboards. Most baseboards or convectors, not radiators(google for more explanation). Cast iron baseboards are very good and won’t get beat up like cheap slant fins you probably have, and are cheaper than Runtals. However being cast iron, they probably won’t perform well at low temps, although to be fair I’ve never tried it. I don’t know how a cast iron radiator or baseboard would do at 120 degrees for example. I think it would take a very long time to heat up. Maybe others would comment.
6. Yes an outdoor thermostat(ie an outdoor reset) is worth setting up if you have the a condensing boiler that can accomodate it. There’s a whole controversy about outdoor resets, and cycle times and modcon boilers you can learn about, but my intuition is it’s probably better to run longer cycles with a high turndown ratio and a lower water temperature than to short cycle the boiler at a high temp, so that’s what I’d shoot for.
I doubt the solar thermal is the best use of your resources. Solar for a heating system will perform the worst when it is needed the most, when it is cold and the solar gain is lower(ie it is grey or dark outside). I’d probably use my solar space for solar electric which can get watts in the summer when you’re using AC, and also run the heat pump in the winter. With a solar thermal you’ll also need antifreeze which can corrode the pipes and it’s a whole thing that you’ll get sick of fast, and frankly, it won’t produce enough hot water to make any difference in your heating system.
So good luck, and please keep us posted on what you learn, and what you decide to do and how it works out, so we can all save energy and maybe a few bucks!
Thanks,
Urbandad
BklnRefugee | 4 years and 4 months ago
I have solar thermal out at vacation place in Montana. You don’t need necessarily need glycol, if you have the right kind of drainback system. We don’t have glycol in ours, and obviously we are dealing with a place where you’ll have a week or two a year of -20F temps. It is true that the solar thermal does not help much in the dead of winter (covered in snow, not much sun), but then again our solar PV (we have both) does nothing in the dead of winter, either. The big thing for solar thermal is the relative cost of your heating fuel vs your electricity. Out where we are, electric power is cheap and our heat fuel source (propane, delivered by a truck) is relatively costly. If we were in a situation where we were using a heat pump rather than a condensing boiler, I think we’d probably have done solar PV only.
Master Plvmber | 4 years and 4 months ago
Urbandad, you might want to read, say, a second book before posting an 863-word opinion piece on hydronic design.