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Converting Steam Systems to Hot Water Systems
Are you thinking of converting an old steam system to a hot water system? Many steam systems are very inefficient due to a lack of maintenance over the years and an old, oversized, inefficient boiler. Converting a steam system to a hot water system can be very costly and may create some issues. There have also been many steam systems converted with no problems. We must ask ourselves these questions.
Why do you want to convert it?
Is it worth the investment to convert it?
Should I improve the existing steam system?
It has been estimated that converting from an old steam system to a more efficient hot water system could save you between 15% and 60%. They usually average this around 35%. I think this should be closer to the high side with the products on the market today. That is, of course, if the new boiler is properly sized and properly piped. This system is suitable for newer boilers operating in the mid-to-high efficiency range of 86% to 95%. This is a more expensive boiler, which requires more maintenance, but is an excellent choice for this type of application. The mod/con boilers are more efficient when cooler water returns to the boiler. Steam-to-water conversions typically operate at a significantly reduced water temperature. The installation costs vary depending on your location and the specific requirements for the conversion.
Is there a payback or breakeven point at these costs? You need to decide that for yourself. How long will you be living there? How high are your fuel bills? What can be done to update your current system, and at what cost-to-savings ratio? Consider the cost and fuel usage. Calculate the savings and look at the payback.
We will examine this from several angles. The first will be what to look for in a steam system before considering a conversion, how to size the new hot water boiler, what needs to be done before converting to hot water, and how to make the conversion.
Surveying the System Systems
2. Do the radiators have one or two pipes connected to them? In only one case will you pay more for all the return piping to be installed and run back to the new hot water boiler.
3. Do a room-by-room heat loss for the building. A heat loss calculation will provide the heat lost per room and the total building loss, allowing you to size the boiler properly. Check the heat output of each room radiator and compare it to the radiator's rated output. You will likely do this, but it's necessary to verify that the radiation can heat the room.
Steam radiators heated with steam put out 240 Btu per square foot of radiation. When heating with hot water, the radiation will only put out 150 Btu per square foot of radiation. Do the heat loss and measure the radiation. Divide the heat loss by 150, and the answer should be equal to or less than the radiator square feet in that room.
Example.
A heat loss for a room is 6200 BTUs. The radiator is 45 square feet in area.
6200/150 = 41.3 sq. ft. This room will heat fine. If the radiator had been less than 41 sq. ft., it would have been a problem.
Size the new boiler per the heat loss, not the radiation. If you size the boiler based on radiation, you will install a larger boiler than needed, which will result in short cycling and higher fuel and maintenance costs.
4.Do not get rid of the cast iron radiation! Cast iron radiators have a significant percentage of their heat output as radiant heat. Radiant heat does not create air currents. Air currents increase heat loss. This is not a huge difference, but every little bit of savings helps. Cast iron radiators produce fewer drafts than almost any other type of heat, including copper tube and aluminum baseboard. Radiant in-floor heat is the only heating style that surpasses cast-iron radiators. The cast iron radiators will create a more comfortable home utilizing less fuel.
2. What to do before we start?
1.First, run the steam pressure up to 10 psi and check for leaks. I usually do this with a flashlight, as it will reflect off the steam. Some people use a mirror to see if it steams up.
2. If there are return lines on the radiators, are they big enough to carry the water back to the boiler?
3. Determine if you have wet or dry returns. If you have wet returns, plan to replace them or, at the very least, the first 10 feet or more from the boiler. They have collected a lot of dirt through the years.
4. If using the same boiler due to not being very old, verify with the manufacturer if it can be converted to water and if they offer a conversion control kit.
5. Determine the water pressure you will need to be operating at.
6. How many zones do you want? Is it doable? Be careful here. Often, the mistake made here is over-zoning, which causes the boiler to short-cycle.
3. How to Convert your system
1. Pay special attention to piping. I suggest using primary/secondary piping at the boiler or utilizing a buffer tank. There will be too much water in the system for all the water to flow through the boiler, maintaining a good delta-T through the boiler.
2. Size your circulator to the heat loss of the system, which is doing a single zone. If you are working with multiple zones, size the zone circulators according to the heat loss in each zone.
4.Size the expansion tank according to water volume and water temperature rise. Do not use the manufacturer's charts for these installations. The charts do not work well with steam-to-water conversions and gravity hot water installations.
You can determine the system piping water volume here, add in the radiation, then add the boiler water volume to the total gallons of the system.
5. Set the heating curve to match the system load as compared to the heat loss.
4. Boiler information, piping andf what to expect upon completion
1. Choose the boiler design of choice. You can use a cast-iron boiler or a high-efficiency boiler with an efficiency rating of 95% or higher. If this is a larger system, you may want to consider using multiple boilers. It is imperative that, when leaving any old iron pipes, a magnetic strainer be installed on the return side of the boiler(s) to protect the boilers and circulators.
2. Good even heat throughout zones or entire system. Ensure the thermostat cycle rate per hour is set to 'Gravity Hot Water' or 'Steam'. One may be better than the other depending on the amount of radiation in your system.
3. Noise-free operation. There should be no expansion noises. The steam-to-water system should always have an outdoor reset control installed to maximize comfort and minimize fuel bills.
4 Little, if any, pressure fluctuation on the pressure gauge.
5. Increased comfort levels
6. Substantial fuel savings.
We have a seminar for more in-depth information that you can view for a small fee. Don't hesitate to get in touch with us to view it or have me do it for your group.
Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, and installations should be reviewed on a per-job basis. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or its personnel accepts no responsibility for improper information, application, damage to property, or bodily injury from applied information found on this website, as it should be reviewed by a professional.