Fan in a can

foresthillsjd

Currently, the boiler and the hot water heater are in a boiler room In my basement, with an open window.  It’s getting cold, and even thought I have heat trace in the pipes most at risk for freezing, I’d like to install a fan in a can kind of setup.  It looks like I need the CAS-4 model, plus the control for the gas water heater.  Is there any way to introduce a powered damper that is wired into everything and only opens when needed?  

Also, will any old plumber know how to install this?  I 200% prefer to have a professional do it. 

Thanks in advance!

Zman

You are going to want a boiler technician. The boiler should be easy. Tell us more about the water heater, they can be more challenging.

jhewings

A damper on the boiler flue is very common and a good thing because less heat escapes from the boiler water after the boiler cycle is complete. Then water stays warmer and the on next cycle the water reaches a boil faster so less fuel consumption. There will also be less warm air from the basement going up the chimney. A powdered damper for make up air is also a good thing but can be a big job to cut a hole in your exterior wall to install the damper especially if it is a brick wall.. Both dampers should be automatically controlled when the Tstat calls for heat so the wiring must be correct. You probably don't need a "steam" guy to install these dampers. A good HVAC guy can do it. For the boiler flue damper, I suggest you check with your boiler manufacturer and buy the recommended damper and the wiring cable that comes with it. I have the 2 dampers mentioned but nothing on the atmospheric water heater.

I have also seen just an open pipe to the outside, 4" or 6" or bigger for make up air. With no damper.

EdTheHeaterMan

I can think of 2 methods to control your damper on an atmospheric water heater.
1. Pressure switch added to the gas outlet of the thermostat valve. 
2. Temperature sensor on the flue pipe connector 

ratio

The hard part will be disabling the water heater burner until the combustion air damper proves open. I don't think it can be done without some kind of non-standing pilot water heater.

EdTheHeaterMan

ratio said:

The hard part will be disabling the water heater burner until the combustion air damper proves open. I don't think it can be done without some kind of non-standing pilot water heater.

 There should be sufficient air for combustion in the room until the damper opens. This is not rocket surgery!  Use your brain science.  How much time does it take to open a damper once a pressure switch is engaged?   The problem is how to shut off the burner if the damper fails to open

maybe an end-switch connected to a time delay circuit that will interrupt the pilot thermocouple circuit in 30 seconds.  No end switch activation = pilot interruption in 30 seconds.  1 minute later the main burner closes

Same concept was approved for power vent kit that operates Field SWG series for water heaters in the 1980s. Still available today

PS

no offense intended @ratio. The brain science thing just worked well with Rocket Surgery 

ratio

EdTheHeaterMan said:

no offense intended @ratio. The brain science thing just worked well with Rocket Surgery

None taken, @EdTheHeaterMan. Like I said in a different thread, I leave my feeling at home most days. It just doesn't pay to take it along any more.

Sometimes I have a hard time picking Good Enough over Just Right. It's a personal failing, I don't let it bother me much.

dopey27177

Why all the dampers and controls.

Te burners for both units need a certain amount of cubic feet of air hour.
calculate the cfh. that will translate the size of the opening needed to supply all the cubic feet of air.
Next Make the window smaller. In the space that is left over install a fabricated elbow and driop a duct to the floor.

The cold air entering the boiler room will not cause any thing to freeze, primarily because the amount of air entering the boiler room is far less than an open window, also the combustion air is delivered to the floor.

jake

JUGHNE

In the boiler I&O manual, there will be a requirement formula for cubic feet of air available for combustion.
You would add the input of the boiler and water heater for that basis.

Often the entire basement cubic area can be used if there is a louvered door on the boiler room allowing the entire basement air to be part of the calculation.

Codes vary, but some times here, if there is a louvered door at the top of the stairs than that air also contributes of the volume of air.

I had a commercial boiler change out job. The existing louver to the outdoors was just a little short of meeting the requirements. So the boiler room volume plus the entire volume of the 4 x 4 pipe tunnel was calculated and provided the additional capacity. That was with the 2 fire doors shut to the boiler room as required (school house).....actually they are usually left open....but closed when the inspection was done.

The Fan in a Can is a noise nuisance with more devices to fail causing shut down.
If actual outside air is needed, often a piece of insulated flex duct, from exterior hood, brought down to the floor and hanging in a bucket for condensation dripping and room air mixing.
This may supplement the basement volume if it is permitted.

Corktown

@foresthillsjd, I’m curious. When you asked about a damper, did you mean for the boiler and water heater, or for the CA-4 itself? ....

EdTheHeaterMan

I’m talking about combustion air inlet.  The “Fan in a Can” the OP referenced is to provide combustion air. To keep the free air “always open” vent from letting very cold air into the boiler room and causing a pipe to freeze.  That is what the discussion started as

Corktown

Thank you for your response, @EdTheHeaterMan Turns out I was on the same page as you. I just wanted to make sure I was understanding what was being asked…

rick in Alaska

I have taken a piece of 6" pipe and brought it down to the floor, and then back up a ways to give it sort of a p-trap effect, and it seems to work well to keep the cold air from just leaking in when things are off. Also very cheap to do.
Rick

Bob Harper

ASHRAE conducted a study overwhelmingly proving passive MUA systems are wholly unreliable while mechanical MUA systems are. You are trusting the inlet is located in zone that will always be higher pressure than the CAZ. A wind shift will change this. You are also assuming the CAZ is under negative pressure. If it is, then you may get venting failure.
The passive MUA ducts with traps do work to an extent but will always be flowing cold air if the delta P is in its favor. This, as noted, can lead to freezing pipes or excess heat load.
An interlocked mechanical system is reliable and only runs on a call for heat. It will not be introducing warm moist air in summer if you forget to close the damper.