Steam to Water Conversion

Converting Steam Systems to Hot Water Systems

There are a lot of homeowners thinking of converting their old steam system to a hot water system. There are many old steam systems which are very inefficient due to lack of maintenance through the years and an old oversized inefficient boiler. It can be very costly to convert a steam system to hot water and may create many problems. 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 just improve the existing steam system?

It has been estimated that by converting from an old steam system to a high efficiency hot water system could save you between 15% and 60%. They usually average this around 25%. I personally 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 is a good system for the newer boilers running in the mid to high 90% range. 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 while cooler water returns to the boiler. The steam to water conversions usually operates at a greatly reduced water temperature. To address the second question, it could cost as high as $15,000 to $20,000 or more to convert to a hot water system. It all depends on where you are located and what needs done for the conversion. Is there a pay back or breakeven point at these costs? You need to decide that for yourself. How long are you going to live there? How high are your fuel bills? What can be done to update your current system and at what cost to savings ratio. Look at the cost and the fuel usage. Calculate a savings and look at pay back.

We will look at this from a few different angles. The first will be what to look for in a steam system before thinking too hard about converting it, how to size the new hot water boiler, what we need to do before we convert to hot water, and how to convert it.

1. What to look for before you get too involved in this project.

Let's look at the radiators first. If you look at the bottom of the radiators you will see all the vertical sections are all connected (touching) at the bottom. Are they the same at the top? If not, you may want to avoid this conversion. It will add anywhere from $2000 to $10,000 more. Do the radiators have two pipes connected to them or just one? In only one you will pay more for all the return piping to be installed and run back to the new hot water boiler. Next do a heat loss for the water boiler. A heat loss will tell you what size boiler to install and also you can determine if you will have enough radiation. You more than likely will but do the heat loss and measure the radiation to verify. The radiation heated with steam puts out 240 Btu’s per square foot of radiation. When heating with hot water the radiation will only put out 150 Btu’s per square foot of radiation. Do the heat loss and measure the radiation. Divide the heat loss by the total square feet of radiation and verify the answer is equal to 150 or less. If so, you have enough radiation for the conversion. Size the new boiler off the heat loss not the radiation. If you size the boiler off the radiation you will put in a bigger boiler than needed and it will short cycle costing you more in fuel and maintenance.

Do not get rid of the cast iron radiation! Cast iron radiation has a big percentage of heat output is 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 radiation produces less air currents than any other heat including copper tube aluminum baseboard except radiant infloor heat.

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 on replacing them. 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 do they offer a conversion control kit.
5. Determine the water pressure you will need to be operating at. 
6. How many zones you want. Is it doable? Be careful here. Many times, the mistake made here is over zoning and causing the boiler to short cycle.

3. How to Convert your system

1. Pay special attention to piping. I suggest the use of primary/secondary piping. There will be way too much water in the system for all the flow through the boiler. It will work better to mix the water from the boiler to that water volume rather than send all the water through the boiler.
2. Size your circulator to the heat loss. If doing multiple zones size the zone circulators (if used) for the heat loss of that zone. If using zone valves size the circulator for the total heat loss and use a differential bypass valve.
3. Size the piping properly. See pipe chart
4. Size the expansion tank according to water volume and water temperature. 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, than 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. What to expect when conversion is completed.

1. Good even heat throughout the entire zone or system if not zoned. Make sure 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 the radiation in your system.
2. Noise free operation. There should be no expansion noises. The steam to water system should always have an outdoor reset control installed so we do not overheat the systems.
3. Very little, if any pressure fluctuation on the pressure gauge.
4. Increased comfort levels 5. Substantial fuel savings.

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, installations should be reviewed on a per job situation. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or it's 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.