Cruise control for your hot-water heating system

Last week I talked about how sustained flue-gas condensation can shorten the useful life of a cast-iron hot water boiler. Today I’d like to share with you my favorite method for preventing flue-gas condensation while making your home more efficient and comfortable.

The goal of any control and/or piping strategy designed to eliminate sustained flue-gas condensation in a cast-iron boiler is to maintain the return water temperature above the dew point of the flue gasses. With natural gas this dew point is typically 130˚ - 140˚F. There are several variables that contribute to the returning water temperature and to the flue-gas temperatures. These include the type of room heat emitter, the volume of water in the system, the size of the boiler (as compared to the heat load) and the ambient combustion air temperature, to name just a few. All of these variables are unique from system to system. They can also change from cycle to cycle in the same system.

Here’s an example: Let’s say you have a system with cast-iron radiators and large distribution piping. This may originally have been a gravity hot water system from the early 20th century. There’s lots of water and metal to heat up in a system like this. Let’s also imagine it's a been a sunny but cool day so your home has benefited from solar gain during the day and the boiler hasn't fired for hours because the thermostat is in that south- or west-facing dining room. The sun goes down, the dining room cools, the thermostat calls for heat and your boiler fires up.

Now think about the water inside your heating system. It’s been sitting there all day in the cold pipes and radiators. It can’t be any warmer than the air in your house or basement — probably 60˚ - 70˚F. It starts to circulate through the boiler, the piping and the radiators. Maybe it runs for a half hour or so, and the boiler manages to heat the water up to about 80˚ or 90˚F. (Remember, flue gasses are condensing this whole time.) Then the thermostat becomes satisfied and the boiler shuts off.

An hour later the thermostat calls for heat again. This time the system warms the water a little more — but still not to the point where condensation is eliminated.

These cycles continue throughout night with each subsequent cycle warming the water a little more, until finally it reaches a point where the return water temperature rises above the flue gas dew-point. Most of the cycles in this particular (but very common) example share the fact that they’re producing low return-water temperatures. It’s the temperature of the returning water that changes from cycle to cycle.

What’s needed to prevent this condensing condition is a control and piping arrangement that can adjust itself dynamically to the changing system conditions. I’ve found that a variable-speed injection-mixing system works perfectly in this situation.

Injection mixing controller

It involves some piping changes near your boiler and the addition of a small, electronic controller to manage the temperatures and control a mixing circulator. The system piping is separated into two loops — a primary loop out of the boiler and back in, and a secondary loop that just circulates water out to the radiators and back. Then I connect those two loops with a piping “bridge,” and hot water from the primary (boiler) loop is “injected” into the secondary (distribution) loop. The controller monitors the temperatures of both loops and adjusts the rate of injection in order to maintain a minimum boiler-loop temperature. It does this by speeding up or slowing down the circulator in the “bridge” to let the boiler catch up to the distribution system’s ability to take the heat away. The beauty of this system is that it can automatically adjust for varying system conditions and provide continuous boiler protection.

Another feature of the electronic controller is its ability to adjust the boiler and the system water temperature in relation to the outdoor temperature. This is called outdoor-reset control. A sensor reads the outdoor temperature and feeds that information back to the controller which then determines the temperature water needed to heat your house at that moment. It can allow the secondary (distribution) water temperature to modulate between, say, 70˚ on a warm day and 160˚ on a cold night. It will also modulate the boiler’s set-point temperature while never letting it drop below its condensing temperature. It’s like cruise control for your heating system — just the right amount of heat at the right time with long, low-temperature cycles.

Outdoor-reset control can save a significant amount of fuel, especially in the “shoulder” seasons when your boiler’s full output isn’t needed.  It will also make your home more comfortable. By lowering the distribution water temperature, each heating cycle is longer and the room temperature swings are minimal, making you more comfortable.

If you have a home that’s heated by a cast-iron boiler and has a high-mass distribution system (such as cast-iron radiators or radiant heat in a concrete floor), you will benefit from this control strategy. Longer boiler life, lower fuel cost and more comfort is a win, win, win!

Heidronically yours,

Wayne

How to kill a workhorse

The vast majority of residential hot water boilers in service today are cast-iron mid-efficiency boilers. These are the workhorses of the hydronic industry and have been for many years. Installed and maintained properly, they can provide reliable service for 30 years or more. They typically have efficiency ratings in the low 80% range, meaning about 80 cents of every fuel dollar spent is converted to useable heat. The rest is lost up the chimney.

Older cast-iron water boilers from the early part of the 1900s were larger and held more water volume than today’s models. While this larger volume of water acted as a buffer and helped to smooth out some of the variability in water temperatures, it was at the expense of some efficiency. Today’s cast-iron boilers are smaller, and consequentially more efficient, but are less forgiving when it comes to handling low water temperatures.

Sustained low water temperatures can cause flue gasses inside the boiler to cool to the point that they condense on the relatively cool cast-iron heat-exchanger surfaces. This condensate is corrosive and will attack the bare metal surfaces of the boiler, creating rust and scale that can plug flue passageways and interfere with the operation of the burner. At its worst, this condition will allow dangerous products of combustion to enter your home. But at a minimum, it will shorten the useful life of your boiler. Today’s cast-iron boilers need to maintain water temperatures above the 130° - 140°F temperature range to prevent flue gas condensation.

The key to maintaining these safe water temperatures lies in your boiler's ability to produce heat at a faster rate than your house can use it.

Copper finned-tube baseboard

An example of a system that would work well is a home with copper finned-tube baseboard and small copper distribution piping. Many homes built in the 50s and 60s fit this description. Considered a “low-mass” distribution system, its copper tubing and light-weight baseboard emitters heat up quickly. These systems are usually designed for fairly high operating temperatures—typically 180°F. Assuming the boiler is sized properly to the home’s heat loss, it can come up to temperature quickly and has no trouble staying ahead of the home’s heating load. Water returning to the boiler will remain above the 130° - 140°F range for most of each heating cycle.

Where flue gas condensation problems start to develop are in high-temperature/high-mass systems, or low-temperature/high- or low-mass systems.

Cast-iron radiator.

A very common high-temperature/high-mass system where sustained flue gas condensation needs to be considered is an older (early 1900s) home with cast-iron radiators and large steel distribution piping. There are literally tons of cast iron and steel, and hundreds of gallons of cold water that need to come up to temperature before the radiators can start heating your rooms. This can easily overwhelm a properly sized boiler and cause it to run at sub-130° temperatures for long periods of time.

Another type of system that can overwhelm a boiler is a radiant in-floor system of tubes in concrete. This one is a one-two punch for your boiler. Not only are these systems designed to run at low water temperatures (110°F is typical) but the entire concrete slab must be heated before it can start delivering room heat. Some of these systems take days to recover from set-back. And the flue gasses are condensing the whole time. It’s a recipe for disaster.

One recent trend I’ve been seeing is for radiant in-floor tubes to be stapled to the underside of the subfloor and connected directly to a cast-iron boiler. This type of installation would typically run at 100° - 130°F water temperatures. The installer simply turns the boiler aquastat, or temperature setting, down to 120° and walks away. This system will likely condense for its entire—albeit short—life.

The effects of flue-gas condensation.

I’ve serviced boilers subjected to these conditions, and believe me, they’re not pretty. Sometimes there are piles of rust on top of the burners.

The good news is there are ways to protect your cast-iron boiler from low return water temperatures, extend its life, improve comfort and reduce your fuel consumption. Next week, I'll tell you my favorite solution to this problem.

Heidronically yours,

Wayne

What every boiler owner should know about indirect water heaters

Indirect water heaters have been around since the 1970’s in this country, but somehow, even after all this time, they don’t seem to be very well understood. They get their name from the fact that they’re heated “indirectly” by your boiler. They’re connected via piping to your boiler and circulate relatively hot (usually 180 to 200°F) water from your boiler to a heat exchanger within the water heater. The water surrounds the coils of the heat exchanger to produce your domestic hot water. This is in contrast to the typical gas- or oil-fired water heater that heats water through the use of a “direct” flame or heat source within the water heater.

If your home is heated by a boiler — any boiler (hot water or steam, oil or gas, mid- or high-efficiency) — you have every reason to heat your domestic hot water with an indirect water heater. Some of the benefits include:

• High efficiency — When you use your boiler as a heat source to produce your hot water, the water is heated at the same efficiency as your boiler. Some high-efficiency boilers reach 96%. The average gas water heater is about 60 - 70% efficient.
• Reduced heat loss — An indirect water heater is very well insulated and loses very little heat during long stand-by periods (at night or while you’re away). A gas water heater is always losing energy up the chimney.
• High performance — The performance of an indirect water heater is a direct result of the boiler it’s connected to. Given the size of most residential boilers, it’s not unusual for an indirect water heater to produce two to three times the amount of hot water as a standard gas water heater.
• Longer life — Most indirect water heaters have a lifetime tank warranty. It will likely be the last water heater you’ll ever need. The manufacturers can offer this warranty because their tanks are not subject to the abuses that a direct-fired gas water heater is. And many of them are made from stainless steel to prevent corrosion.
• Hot water storage. Available in sizes ranging from 30 - 200 gallons or more, hot water can be stored for high-volume flow-rate usage when you need it.

 The photo at right shows a cut-away view of a typical indirect water heater, with the coil located at the bottom. Boiler water is circulated through the coil and surrounded by the domestic hot water in the tank.

“But Wayne,” you may ask, “doesn’t this mean I need to run my boiler all summer now, too? Won’t that cost me a bundle?” Au contraire, my energy-conscious friend. The only time the boiler fires is when you need hot water. And when it does fire, it’s producing hot water at a higher efficiency rate than a typical water heater. Other than that, it sits quietly and waits. The belief that the boiler is running all summer may be a throw-back to the days of tankless coils in older boilers. They had no storage capacity, so the boiler needed to stay hot all the time to produce hot water on demand.

“This is all well and good,” says the the intrepid Internet traveler, “but I’ve been hearing that the new tankless heaters are the greatest thing since Apple went public. Can’t I save a lot more money with one of those?”

Well, speaking of apples, this is really an apples vs. oranges comparison. A tankless heater usually has little or no storage capacity, meaning it needs to heat the water instantaneously. And it can do that — with some limitations. Older tankless heaters drop the temperature at high flow rates (two fixtures running). Newer models limit the flow rate to maintain the delivery temperature. An indirect heater can handle that high flow rate without reducing the temperature or flow. And, depending on the size of your boiler, it can do it while delivering almost limitless hot water.

Better tankless heaters have efficiency ratings in the 80 - 95% range but typically last just 15 - 20 years. An indirect water heater connected to a 15-year-old cast-iron boiler will deliver hot water at 80 - 82% efficiency. And one connected to a modern modulating/condensing boiler can deliver 96% efficiency. So while tankless water heaters are efficient, they can't beat indirect water heaters.

Indirect water heaters can also reduce your maintenance costs. Having only one gas- or oil-fired appliance means less service. A tankless heater needs to be serviced every year. If not, you can count on reduced hot water production, possible heat exchanger failure and loss of warranty coverage. An indirect water heater requires little additional maintenance beyond your annual boiler safety and performance check-up.

The next time you’re in the basement, take a look at your existing standard water heater. If it's a little worse for wear, you may want to remember that the typical water heater life is 12 years. Wouldn't it be nice to replace it — once and for all?

Heidronically yours,

Wayne

# 7 — Humidity: Why a hydronic heating system is better for your home’s comfort level than forced air

And finally we're at number seven of the Top 7 reasons why a hydronic heating system is a better choice than forced air — humidity.

If you’ve lived with a forced air heating system for any amount of time, you’re quite aware of the drawbacks associated with managing your home's winter humidity levels. You’ve experienced the static shocks, the dry throat and skin, the stuffy nose and even nosebleeds. You might even have grown to accept it as a normal part of the winter heating season. Or maybe you invested in a humidifier to add moisture back into your home.

I’m here to tell you it’s not normal. It’s your heating system working against you by drying out the air as it’s being blown throughout your house. Your furnace acts like a wringer to squeeze the moisture out of the air. The air dries up as it’s repeatedly heated up and cooled down. The furnace blower also pressurizes your house — it forces conditioned (heated and humidified) air out of any little cracks or crevices and draws cold, dry air in to make up for the warm, moist air you’ve lost. Then your humidifier kicks on to add that moisture back in. And the cycle repeats nonstop, every time your heat is on.

A hydronic heating system is better for you (and for your home) because it never dries the air out in the first place. A well-designed hydronic heating system generally operates at a much lower temperature than a furnace,  producing much longer and gentler heating cycles. The lower water temperatures keep the relative humidity at a comfortable level. There's also no blower, so there’s less air infiltration, meaning less of your conditioned air (that you're paying to heat) goes out the doors, windows and cracks throughout your house.

Most experts agree that a comfortable range of winter indoor humidity is 25% - 50%. Below 25% and you begin to experience the uncomfortable effects of a dry environment. Above 50% is concern for mold growth. Most of the homes in our area (upstate New York) outfitted with hydronic heating systems have no need for added moisture to the indoor air. There’s usually enough humidity added through showers and cooking that a supplemental humidifier isn’t necessary. Bathroom exhaust fans and kitchen range hoods help to keep the humidity below the high end of the comfort range. (Some very tight, well-sealed homes may require supplemental ventilation to maintain a healthy indoor environment but these are more the exception than the rule.)

Now that we've come to the end of this series on why a hydronic heating system is a better choice than forced air, I'm sure you can see that there are major advantages — not only in comfort, but also in long-term efficiency. And don’t forget the rest of these advantages:

• Reliability
• Versatility
• Quiet
• Cleanliness

I hope you’ve enjoyed reading this information as much as I’ve enjoyed writing it. And please — feel free to comment. I’d love to hear what you have to say. And let me know if you have a particular question or topic of interest you’d like to see discussed here in the future.

 

For next week, I’ll discuss what every boiler owner should know about indirect water heaters. (Also known as, why a boiler owner should never consider a tankless water heater!)

Heidronically yours,

Wayne

# 6 — Cleanliness: Why a hydronic heating system is cleaner than a forced air system

We've made it to installment #6 of the Top 7 reasons why a hydronic heating system is a better choice than forced air — Cleanliness. I hope you're still with me.

A forced air furnace with its blower and duct system will stir up and move dust, pollen and other impurities throughout your home. Some will remain airborne and inhaled while others will land on surfaces and leave a layer of dust that can again become airborne during cleaning. Then the cycle continues. Some of those impurities come to rest and cling to the inside of your air ducts.

Whole industries have sprung up to prevent and remediate the issues created by the "burner and blower" concept of heating. The sale and installation of HEPA filters, UV lights and electronic air cleaners have produced plenty of revenue enhancement for the furnace guys. And it seems duct cleaning services are being offered by everyone with a shop vac — from handy men to furnace guys to cleaning outfits. You gotta admire them, though — invent and sell a heating system that pushes dirt and allergens around your house, then offer add-on solutions to fix it. Hmmm.

As we've discussed in previous installments of Heidronics, your hydronic heating system uses a completely different heat delivery method. Pipes and tubing deliver heat from your boiler to your rooms without stirring up a trace of dust. The radiators, panels and convectors deliver their gentle heat without blowers or fans. The result is a cleaner indoor air environment with less airborne dust and allergens. You'll also find you need to dust less. And, of course, you'll avoid the added expense of replacement filters and duct cleaning.

Another hydronic advantage, especially for low-temperature radiant systems like in-floor or ceiling radiant, is a reduction in dust mite concentrations. Studies have shown that dust mite populations are significantly lower in homes equipped with low-temperature radiant heating. They've also shown a lower incidence of allergic reactions to dust inhalation. You'll find more detailed information at environmental ergonomics expert Robert Bean's website healthyheating.com.

Next week I'll wrap things up (and maybe dispel a myth) with a discussion about humidity. You may be surprised.

Heidronically yours,

Wayne

# 5 - Quiet: Why a hydronic heating system is quieter than forced air

This week's entry in the Heidronics blog is installment # 4 of the top 7 reasons why a hydronic heating system is a better choice than forced air — quiet operation.

Any well-designed, installed and maintained hydronic heating system will be virtually silent. This is true of hot water baseboard, in-floor radiant and even a steam heating system. If there's noise, your system's telling you it needs attention. These are not normal sounds.

A forced air furnace is inherently noisy compared to a hydronic system. Blower noise is the most common complaint. The mechanical whirring of the blower and the velocity noise of the air moving through ducts and across register grills are quite noticeable in most homes. Furnaces marketed as "high-performance" equipment are an attempt to minimize this noise by using variable speed blower motors that keep blower speeds as slow as possible — but the only way a furnace can match the silence of a hydronic system is when the furnace is off.

The ducts of a forced air heating system can also be noisy. The ducts will expand as they heat up and "balloon" as they're pressurized by the blower. This can create the popping or creaking sounds you've heard when the furnace starts up. At its worst, it can be like living in a tin can.

I've also seen forced air systems actually blow doors closed, move curtains and rattle blinds on windows.

Not convinced? Oh — there's more. Electronic air cleaners snap away. Humidifiers hum, hiss and rattle. Dampers shake. I think you get the idea.

Because a hydronic heating system uses a completely different distribution method, you don't get the "side effects" of hot air moving around your home. Water or steam move gently throughout your home via small tubing or piping. Water and steam can do their jobs silently, going unnoticed for months and years at a time.

The bottom line: Silence is golden, especially when it comes to your heating system!

Stay tuned  – next week's topic is cleanliness.

Heidronically yours,

Wayne

# 4 - Versatility: Why a hydronic heating system is more versatile than forced air

In previous blog posts I've talked about how a hydronic heating system is more comfortable, more efficient and more reliable than a forced air system. Today's topic is versatility and this is where hydronics really shines.

There's no more versatile means of heat production, distribution or delivery than hydronics. This may be a bold statement considering all of the heating system choices available today, but let me offer this list as proof positive.

Heat production:

• Traditional cast iron boiler (gas, propane, and oil fired)
• Condensing boiler (gas, propane, and oil fired)
• Modulating/condensing boiler (gas and propane fired)
• Electric boiler
• Tankless combi-boiler (gas, propane and electric)
• Traditional tank-type water heater
• Biofuel boiler (wood, pellets, coal and other solid fuels)
• Solar thermal
• Ground source heat pump (geothermal)

Heat distribution:

• Adaptable to existing steel piping (such as an old gravity heating system)
• Copper tubing
• Pex or pex-al-pex tubing (types of cross-linked polyethylene tubing)
• Series loop, direct return and indirect return systems
• Manifold header system (fed from common source point)
• Home-run system (individual delivery to rooms or emitters)
• Unlimited zoning (zone valves or thermostatic radiator valves)
• Mini-tube (ability to supply heat to remote areas or outbuildings)

 Heat delivery:

• Cast iron standing radiators
• Cast iron baseboard radiators
• Copper finned-tube baseboard radiation
• Steel panel radiators
• Aluminum radiant panels
• Towel radiators
• In-floor radiant heating (tube and plate staple-up, above-floor panels, thin-floor pour (gypsum overpour) and slab radiant (concrete)
• Radiant ceilings and walls
• Hydro-air
• Domestic hot water production
• Snowmelt (for driveways and walkways)
• Pool and hot-tub heating

Hydronics can provide all of this versatility from a single heat source. There's no need to have multiple fuel-burning appliances to perform all of your heating needs. That can simplify the fuel supply, electrical supply, and flue gas venting (chimney) requirements for the entire system. And fewer appliances means less maintenance.

These are just some of the many ways hydronics can be used to make our homes (and lives) more comfortable, efficient and convenient. (I'll go into more detail about some of them in future blog posts.)

Next week I'll write about why a well-designed hydronic system is so quiet, compared to forced air heating.

Hydronically yours,

Wayne

# 3 - Reliability: Why a hydronic heating system is more reliable than forced air

The reliability of your heating system is something you may take for granted – until it's not working. But  hydronics has a long history of reliable service – even when neglected.

The traditional workhorse of hydronics is the cast-iron boiler. You know – like the one in grandma's basement that's been feeding those big 'ol cast iron radiators you used to put your mittens on after coming inside from a sledding excursion. It you go down there today you may find that same boiler just purring along some 30, 40 or 50 years later. With its massive cast-iron heat exchanger sections, it may still be some time before a leak forces her replacement. (I'm still talking about the boiler here!)

Compare that to the sheet-metal heat exchanger of a forced air furnace and there's not much debate. The heat exchanger of any heating equipment goes through thousands of heat-up and cool-down cycles in its lifetime. Each of these cycles starts to fatigue the metal and bring the furnace one step closer to failure. Compare 1/8" (at most) of a furnace sheet-metal heat exchanger to a 1/2" (or more) of cast iron and you begin to see why grandma's old boiler is still kicking while her neighbor, Myrtle, has had the furnace guys replace a couple of "slip unders" in the same amount of time.

Now, I'm not going to tell you that grandma's 40-year-old boiler is as efficient as a modern replacement boiler, but then she's probably thinking, "If it ain't broke, don't fix it", and, with proper maintenance, that can be good strategy.

But another way a hydronic heating system has it all over forced air is in the reliability of its distribution system. Over time, a furnace duct system can develop leaks and build dust and contaminants that blow throughout your home. A hydronic heating system has a network of pipe or tubing that distributes the heat throughout your home with the same reliability and efficiency today as it did the day it was installed. (I've seen systems installed in the 1920's and even earlier, still moving water from the boiler to the radiators.) The pipes can last this long because, after a few days, all of the oxygen is "boiled" out of the distribution water and it no longer has the capability to corrode the piping's internal walls. And leaking pipes just cry out "fix me!" while a leaking duct can go on leaking energy for years.

Many hydronic system owners also choose to heat their domestic hot water (for showers, clothes washing, etc.) with an indirect water heater. (I'll discuss the many advantages of an indirect water heater in a future installment of Heidronics.) It uses the boiler's capacity to heat hot water for domestic use in a separate tank. Many of these have a lifetime warranty and will be the last water heater you'll ever buy. Compare that to the 12 year national average life span of a traditional gas hot water heater. Now that's reliability!

Even though I've seen plenty of older hydronic systems continue to work for years without regular maintenance it's been my experience that any system will work longer (and more reliably) with scheduled, thorough maintenance performed by a competent service technician.

If you're considering hydronics for your home, be sure to ask the designer and installer what provisions they've included in the design and installation to maximize your new system's reliability.

Next week I'll talk about how versatile a hydronics system is – and how that compares to what a forced air system can (and can't) do.

Hydronically yours,

Wayne

# 2 - Efficiency: Why a hydronic heating system is more efficient than forced air

When most people think about their heating system's efficiency they think of that yellow sticker on the side of their boiler that shows the annual fuel utilization efficiency (AFUE) rating issued by the U.S. Department of Energy. It's an attempt by the DOE to express fuel efficiency in annual or seasonal terms. Its accuracy has been debated by much smarter people than me, and could be the subject of a future installment of Heidronics. But for now, at least, I'll spare you the mundane details concerning lab analysis of combustion performance.

In my opinion, AFUE is a convenient, high-level measure of efficiency between "like" equipment — for instance, to compare one cast-iron mid-efficiency boiler to another, or one modulating-condensing boiler to another. In real-world terms, AFUE is not a fair way to compare different heat sources like a high-efficiency, condensing furnace to a condensing boiler. There are just too many differences in how these appliances are built, used and applied to make any kind of useful comparison.

What the AFUE ratings will tell you is how much of the fuel you've purchased is converted to useful energy, and how much is wasted up the chimney. A 90% efficient boiler will (theoretically) waste 10% of its energy, or 10 cents of every dollar, up the chimney. What the AFUE ratings don't (and can't) measure is how efficiently that useful energy is delivered to the rooms in your home.

When a boiler produces heat, it transfers that heat to water and delivers it through piping to the rooms in your home. Once in the room, the water's heat is delivered through a radiator or convector to heat the people, objects and air in the room. Water is a great conductor of heat and radiation is an excellent means to deliver that heat where it's needed. (You may recall that in last week's blog post, I discussed the various ways that hydronic systems make you feel comfortable.) Very little of the heat produced by your boiler is lost in the process of delivering it to your home.

When a forced air furnace produces heat, it transfers that heat to air and delivers it through ducts to the rooms in your home. Once in the room, the air needs to move through the room to heat the people and objects. This delivery system is ripe with opportunities for inefficiency. For starters, air is a poor conductor of heat and ducts are notorious for leakage. Because heat needs to move through the room to do its work, it creates air movement across your skin, which has a natural cooling effect. The furnace's blower also pressurizes the room, forcing heated air out of any crack or seam in the walls, floors and ceilings.

A furnace may be able to produce heat with efficiencies that rival a boiler, but it just can't compete with the distribution efficiency of a well-designed and installed hydronic heating system.

Next week I'll talk about the reliability advantages of hydronic heating systems.

Heidronically yours,

Wayne

# 1 – Comfort: Why a hydronic heating system is more comfortable than forced air

To answer this question, if helps to first understand how your body reacts to a room environment and how you know when you're comfortable.

A common misconception is that the way to make your home comfortable is to provide enough heat to keep your body warm. In fact, your body loses heat to its surroundings and the rate of that heat loss is what makes us comfortable – or not. You may remember from science class that heat always travels to cold because the environment is always trying to achieve thermal balance. Your body reacts the same way to its environment – giving off heat to the surrounding air and surfaces. The rate at which your body gives off that heat determines your comfort level. The slower your body gives up its heat, the more comfortable you feel. The job of your heating system is to slow the body's rate of heat lost to the environment.

Your body loses heat four ways:

• Radiation (heat lost to cooler surfaces in the room)
• Convection (heat lost to the air around you)
• Conduction (direct contact with cooler surfaces)
• Evaporation (from your skin)

About half of this lost body heat is through radiation, with another third through convection, and smaller amounts to conduction and evaporation.

Of these four, a hydronic heating system uses radiation as a large component of its heat-delivery method – which means it heats the objects in the room rather than just the air. Your body senses these warmer surfaces and gives off less heat to them. A forced air furnace delivers warm air to the room and heats the room surfaces through conduction, resulting in cooler surfaces and a less comfortable environment.

A hydronic system also delivers heat through convection. This creates a gentle, natural air flow as cooler room air flows across the radiator and is warmed by conduction. This air flow is imperceptible to your body but acts like a blanket of warmth. By contrast, a forced air furnace creates air flow using a blower, causing a cooling effect when that air contacts your skin. It's the same feeling you get when standing outside on a sunny but breezy day. The thermometer may indicate that the air temperature is warm, but the sensation on your body is that it's cooler.

Because the surfaces in a hydronically heated room are warmer to the touch, you lose less body heat and feel more comfortable when you touch other things or surfaces in the room. A great example is a radiantly heated floor. Your feet lose no heat to the floor, so your body feels more comfortable – even at a lower room air temperature. A conventional, forced air heated room will often have a “comfortable” air temperature but you'll feel cold because your feet are in contact with a floor that is several degrees cooler than the air, and much cooler than your body.

The last way your body loses heat is through evaporation. Your skin cools as its moisture is lost to the surrounding air. A hydronic heating system doesn't dry out the air as a forced air system will. This reduces the evaporative effect on your skin and leaves you feeling more comfortable.

When it comes to comfort, hydronic heat offers clear advantages over forced air.

Next week I'll discuss how hydronic heating systems are more efficient than forced air.

Heidronically yours,

Wayne

Top 7 reasons why a hydronic heating system is a better choice than forced air

1. Comfort – Your body naturally loses heat to the cooler surfaces in a room (windows, walls, floors and furniture). When those surfaces are warmer, you feel more comfortable. No system is more comfortable than a hydronic system, because it heats the objects and surfaces in the room. But because a forced air furnace heats the air, you only feel comfortable when the furnace blower is on.
2. Efficiency – There's more to heating efficiency than just the AFUE (annual fuel utilization efficiency) rating of a boiler or furnace. For example, a furnace blower can pressurize the room and force heated air out through small cracks in a building's walls, roof and floors (also called the “building envelope”). Hydronic heating systems don't pressurize the room during heating cycles, so there's less heat loss.
3. Reliability – It's not unusual to find well-installed 30- or 40-year-old cast-iron boiler still providing reliable service. Forced air furnaces have a typical lifespan of 15 - 20 years.
4. Versatility – The design flexibility of a hydronic system makes it exceptionally versatile. Systems can be configured to provide independent heating zones, domestic hot water or snowmelt, as just a few examples. A hydronic system is also a perfect complement to a ground-source heat pump (geo-thermal). A forced air system can't begin to compete in this category.
5. Quiet – There is no quieter heating system than a well-installed hydronic system. (If you hear a lot of noise in the pipes, something needs fixing!) Compared to forced air's noisy blower and frequent on-off cycles, there's just no contest.
6. Cleanliness -- With no blowers or leaky ducts, there's no dust blowing through the house. That means there's less housecleaning plus a healthier indoor environment, especially for people with allergies.
7. No need for humidification – A hydronic system doesn't dry out the indoor air because its water temperatures are usually much lower than the air temperatures of a forced air furnace. Because forced air makes indoor air so dry, most people need additional equipment (such as a humidifier) to add moisture back into the air to feel more comfortable.

Stay tuned. Starting next week, I'll expand on each of these seven advantages in more detail.

Heidronically yours,

Wayne

What is a hydronic heating system?

Webster's defines hydronics as “of, relating to, or being a system of heating or cooling that involves transfer of heat by a circulating fluid (as water or vapor) in a closed system of pipes”.

If you live with a hydronic heating system, you might define it as comfortable or efficient, or quiet, or all three.

It can be as simple as a 1950's system consisting of a cast iron water boiler and simple finned tube baseboard radiators. It can be “old school” hydronics like a 1920's one-pipe steam system with cast iron standing radiators. Or it can be a modern, state-of-the art high-efficiency system consisting of a modulating, condensing boiler and radiant panels.

It's luxurious comfort. But if you've ever lived with a hydronic heating system, you already know that.

Using water or steam as the medium to transfer heat from the source (boiler) to the living space is an incredibly efficient and versatile system. Unlike forced air heating systems, very little heat is lost in the delivery process. And with a radiant hydronic system, that heat is delivered directly to the objects and occupants in the room.

Hydronic heat can be used with traditional cast iron radiators or copper finned tube baseboard, modern panel radiators, radiant floors, radiant ceilings (yes, ceilings!) and walls, towel warmers, and much more. Modern controls provide energy conservation through zoning and outdoor reset control and added comfort with indoor reset and floor sensors. It can also provide almost unlimited quantities of domestic hot water for showers, laundry, and other household uses.

While the official definition is all about water, I think it's really all about comfort.