Hot Water - Are the wall hung models really better

john_170

Homeowner here. I would really apprecate any advice on whether the wall hung model is the way to go and the best way to vent. They say they are the most efficient but I heard there were problems with some a few years back and do they really last as long as the floor cast iron models or are they just easier to install? We are in the process of trying to decide which hot water boiler to go with and do we go with a flue up the house or vent out the side of the house. Each professional has a different opinion. Any advice would really help. Thanks.

Al Letellier_9

which is better

they all have their pluses and minuses. You didn't mention what flue you are using. Wall hung boilers are dedicated to gas only. Floor mount cast iron boilers are durable but can be less efficient overall. Gas fired wall hung boilers are usually vented side wall and can be of higher efficiency that anything else, but the BTU value of gas is lower that oil. A good pro will help you decide what is best for your application.

Glenn Sossin_2

Popular applicance outside the US.

Many other countries are using wall hungs. They take up less space, use less energy, can be vented right out through the wall or up a chimney, or even installed outside, and can be easily installed by 1 mechanic.

The two main problems that occur most often, undersized gas lines, and improper flue connections.

These types of units don't store water, they make it as you use it so the btu requirements can be several times higher than conventional water heating equiptment. Depending on the model and manufacturer, they usually are rated somewhere between 145,000 and 250,000 btu's or more.

As a quick estimate, each 40,000 btu's will create a 1 gpm flowrate where the water is raised approx 65 degrees. An example would be, your starting water temp is 50F and you raise it 65F - you end up with 115F discharge water.

So if you had a unit with a btu rating of 240,000 btu's, it would produce approximately 6 gpm at a 65F rise. This should be enough to comfortably handle 2 showers at the same time. A unit rated at 199,000 would make just under 5 gpm at a 65F rise. This is about as low as I would go if you want 2 showers at the same time.


There 2 basic venting scenarios, a single vent and double vent system. The single vent basically is a single exhaust connection. You need lots of free air for combustion - keep in mind, what ever air is being pushed out the vent, is being sucked in from somewhere else.

In the winter time, this can create a negative suction in your home increasing infiltration losses. Depending on the enviornment, it can also plug up your heat exchager and foul up sensors - especially if there is wood working or drywall sanding nearby.

The best setup is a double vent - one for intake air and one for exhaust - also known as sealed combustion. This does not drag dirt and dust into the heat exchanger and does not create a negative pressure situation increasing your heat loss in the winter.

I would suggest you look for a company that has several factory authorized agents in your area so if something does happen, you have someone to call for servicing.

The main drawbacks are they require a minimum flow rate to turn on usually around .65 - .75 gpm and they have a fine filter that can easily plug up with sediment and cause the unit to not fire do to insufficient water flow. Usually, this is a very easy filter to access and clean. They also usually require SS venting and a dedicated flue pipe - they usually can't share the same vent pipe with another appliance such as a boiler.

Recirc lines for this type of product can be a bit tricky but you can be a bit creative with the installation. Say you have a 2 story home, 21/2 baths. 2 baths are back to back on the second floor and the kitchen is relatively close by on the first floor. Why not install the unit in a closet close to the bathrooms or laundry area. This potentially eliminates the need for a recirc line and some hot water piping. You would need to bring a cold water feed line and gas to the heater upstairs, and from that point, branch out with the hot water feed line.

Theres my .02

ScottMP

.02

Glenn, great information, but I belive he was looking for info on Boilers, Not domestic hot water heaters. I thought the same thing untill I re-read his post.

MY two cents on wall hung Boilers , much higher effeciency all around and fuel is only going in one direction. Also less green house gas emmesions.

Win/Win

Scott

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Unknown

not to mention silent!!!

as the reluctant owner of a power vented oil boiler (man, I can't wait to leave it behind) I dream of the day that I have to walk up to the boiler to see if it's firing...

Glenn Sossin_2

Re read

Scott
Your right, isn't the first time, and I'm sure it won't be the last.

I believe most of my comments above would apply but there are a few more to add.

With a few exceptions, most wall hung boilers that I've come across are condensing. The heat exchangers are designed to extract heat energy from the flue gasses to bring them below their dew point. This causes the condensate. When this happens, the boiler is probably operating between 88% - 95% efficiency. The lower the return temp coming into the return of the boiler, the higher the efficiency of the boiler. The exchangers are desiigned/made to withstand the corrosive effectives of the condensate. I would recommend S/S over the aluminum block boilers. The aluminum is more likely to corrode and plug up much faster than any s/s exchanger.

Besides the increased efficiencies, most of these boilers come with indoor/outdoor reset controls and modulating gas burners. In effect, this is like outfitting the boiler with a gear shift and accelerator pedal as opposed to an on/off switch.

An ideal situation for a boiler system is to create/inject heat energy into the buidling envelope = to the amount of heat it loses to the atmosphere. The modulating burner and indoor/outdoor reset, together with a properly designed heating system virtually allow you to reach this goal.

The boilers can be typically installed by a single mechanic. You are not hauling around 400 - 500lbs of iron. They can be installed virtually anywhere - ene an attic. As Bob said, they are very quiet. If your not within 10-15 ft of the unit, you probably won't know its on. I've attached a photo of an attic installation with a wall hung heater.

The can be installed so you are using outside air for combustion. This simply means that you are not drawing air from within the building structure to burn/exhaust the fuel. The volume of exhausted flue gasses for an atmospheric boiler typically comes from within the house. You are creating a negative pressure zone and outside (cold air) is drawn into the house so you can have flue gasses to exhaust.

The boilers themselves are 1/3 the size and weight of the conventional boiler - and occupy less space. This typically allows the homeowner more living/storage space.

Drawbacks are similar to those of the wall hung heater. These products typically have to be vented in their own flue passage - not combined with another appliance like a water heater. They typically cost more. The higher potential energy savings come at a cost - the are more intricate in design, which is why I said you need to be sure there are several factory trained/authorized mechanics in the event you need service. Most these boilers - especially the mod-cons, require yearly inspection/service/cleaning. Not doing this may lead to warranty issues down the line.

The gas pipe sizing for a wall hung boiler will be the same or less than a conventional atmosperic boiler, but you now have to be concerned with proper piping methods. It is very important that the installing mechanic has read/followed the piping methods and venting sections of the manual. Other than simple component failure, this is where most other problems will stem from.

Glenn Sossin_2

Re read

Scott

Your right, isn't the first time, and I'm sure it won't be the last.

I believe most of my comments above would apply but there are a few more to add.

With a few exceptions, most wall hung boilers that I've come across are condensing. The heat exchangers are designed to extract heat energy from the flue gasses to bring the exhaust flue temperature below the dew point. This causes the condensate to form. When this happens, the boiler is probably operating between 88% - 95% efficiency. The lower the water temp coming into the return of the boiler, the higher the efficiency.

It's actually a pretty easy concept. In simple terms, if you send water out of the boiler at say 155F, and it comes back at 125F, that indicates you dropped 30 degrees worth of heat energy out there somewhere. The wider/lower the return temp is, the more heat you delivered into the heating system.

The exchangers are designed/made to withstand the corrosive effectives of the condensate. I would recommend S/S over the aluminum block boilers. The aluminum is more likely to corrode and plug up much faster than any s/s exchanger.

Besides their increased efficiencies, most of these boilers come with indoor/outdoor reset controls and modulating gas burners. In effect, this is like outfitting the boiler with a gear shift and accelerator pedal as opposed to just an on/off switch.

An ideal situation for a heating system is to create/inject heat energy into the building envelope = to the amount of heat it loses to the atmosphere. The modulating burner and indoor/outdoor reset, together with a properly designed heating system allow you to reach this goal.

The boilers can be typically installed by a single mechanic - the installation labor is likely to be less. You are not hauling around 400 - 500lbs of iron. They can be installed virtually anywhere - even an attic. As Bob said, they are very quiet. If your not within 10-15 ft of the unit, you probably won't know its on.

Like the water heater, they typically can be installed so you are using outside air for combustion. This simply means that you are not drawing air from within the building structure to burn/exhaust the fuel. The volume of exhausted flue gasses for an atmospheric boiler typically come from within the building structure. You are creating a negative pressure zone inside which causes outside (cold air) to be drawn in to replace the vented flue exhaust.

The boilers themselves are 1/3 the size and weight of the conventional boiler - and occupy less space. This typically allows the homeowner for a little more living/storage space.

Drawbacks are similar to those of the wall hung heater. These products typically have to be vented in their own flue passage - not combined with another appliance like a water heater. They typically cost more - 25% - 50% or more. The higher potential energy savings come at a cost - they are more intricate in design & control, which is why I said you need to be sure there are several factory trained/authorized mechanics in your area in the event you need emergency service. Most of these boilers - especially the mod-cons, require yearly inspection/service/cleaning. Not doing this may lead to warranty issues down the line.

The gas pipe sizing for a wall hung boiler will be the same or less than a conventional atmospheric boiler, but you now have to be concerned with proper piping methods. It is very important that the installing mechanic has read/familiarized himself with the piping methods and venting sections of the manual. Other than simple component failure, this is where most other system problems will arise from.

I think I have $.03 credit now.

Dave_4

THE DECISION IS SIMPLE....

In Europe – gas and electric is more than twice what it is here and they are using wall hungs en-mass – were you expecting gas and power to buck the upward trend ????

True the technology in the usa is new – but a lot of it is imported, so it’s mature and reliable!!!

ps: i include all modulating-condensing (MODCON) boiler under this catchphrase