Hydronic Unit heater motor question.

[Mark]

Hoping someone can offer some guidance. I do want to state that I will not be doing the work myself but will have a licensed electrician replace the motor in my unit heater if it is a good option. I am asking here instead of playing phone tag with the electrician and waiting two weeks for a call back plus I know there are a lot of experienced folks here that can tell me if I'm thinking in the right direction.

Here's the question:

I have a Reznor vertical hydronic unit heater model hh-175. It's currently used for on-demand heating of a garage. The heater has a 1/30 hp motor that turns at 1550 rpm's. Problem I'm having is that the heater puts out some decent heat and raises the temp of the room but not quite enough to overcome the drafts in the old building when it's really cold out. The hot water to the heater is about 190 degrees which according the heater manual produces about 60k btus at about 550 cfm. The hot water return on the heater is still extremely hot so it appears that the heater does not deplete the heat from the coils all that much. What I'd like to do is put a larger motor on it to try and increase the cfm's to use more of the heat that appears to be available. Doing the also may increase air circulation in the room to spread the heat around a bit more also. Does this sound like a good or a bad idea ?

Thanks,

Mark

[Edwin Pawlowski]

Not hard to do for a DIY. I used to run the assembly line for unit heaters that compete with Reznor.

I am asking here instead of

Bad idea.

Changing the motor is not going to give more CFM unless it turns at a higher rpm. A 1/30 hp motor at 1550 will give the same volume of air as a 1/2 hp motor at 1550 with the same fan blade. I cannot speak for Reznor, but we used to offer two fans on a given model, one had a higher output. There were still limits as to the amount of heat that a given coil will produce.

Increasing the flow of air over the coil is not necessarily going to extract more heat. You need a certain amount of "residence time" for the moving air to pick up the heat from the surface area of the coil/fins. It may move it to other sections of the room, but it is not going to give off more heat. You can get the same result by putting a secondary fan to help move the air to where it is needed.

In truth, you can get more heat from the coil with lesser air flow. That gives the air more time to pick up the heat. What it also does is reduce the circulation. It will be much hotter at the heater, but much cooler in the far areas of the room.

When I worked for the Nesbitt Company years ago, we had some pretty smart engineers trying to wring out as much heat as possible from a given heater design. You need some balance between air flow and temperature. I'm sure Reznor did the same.

If you want to get more heat out of the water line in the room, add more surface area. After the heater add sections of finned tube. Or add a second heater with blower. Ed [e-mail]

[CBHvac]

First, I would not hire an electrican to do a HVAC techs work.

Bad. The other post repeats about what I was going to say..

[CLSSM00X7]

Hi,

190 degrees is very hot. Most hydronic heating systems are run about 140 degrees. Make sure your fan coils are clean also. I like your idea. You should have a ten degree difference in the temp of the incoming and outgoing water in the loop. I would increase the flow and drop the temp if it were me. This can be done with a higher horse motor and a fan with a higher flow rate of air. The pitch on the blades can increase the ccf. You'll need a different motor of the same rpm with at least a 1/15 hp.

candice

[CBHvac]

Wrong. Try 190 is about right...res units run between 180-195F

What drugs and or thought of simple thermodynamics are you on? You should stop trying to answer questions that you have no clue about. One day, its gonna bite you on the ass.

[Stormin Mormonn]

1/30 is a pretty small motor. You can either try and get a larger motor for that one. Another thing that sometimes helps is to put a fan blowign towards the heater. Circulate the newly heated air into the room.

Yes, I said "towards" the heater. Seems to work better than blowing from the heater towards the room.

[Edwin Pawlowski]

Thanks for the information. I had not realized they changed the law of physics and how they affect thermodynamics. I'll pick up a new book. Ed

[Mark]

Thanks everyone for the informative answers. I do have another one of these heaters that I can hook up but was hoping to take the cheap way out and avoid chopping into the pipes since the system is all winterized.

Mark

[POPPYPLANK]

Mark

Before you start hackin and whacking

One question

Are the fins on the coil clean...you never indicated how old or how long this unit had been in service.

If the fan is running with your really low delta t between supply and return and lack of heat from the heater; a good cleaning may be in order

Or it could be one of maybe 48,345 things but have fun

Vic Plank Lancaster PA

First snow of season tomorrow

[Mark]

Vic, It's actually a new unit heater, only been in use for about 2 weeks, coil looks good and clean. The heater seems to push out a good amount of heat but not quite enough to overcome the heat loss from the building..

Mark

[HvacTech2]

Hi CLSSM00X7, hope you are having a nice day

On 02-Dec-03 At About 02:01:07, CLSSM00X7 wrote to All Subject: Re: Hydronic Unit heater motor question.

C> From: [e-mail] (CLSSM00X7)

C> Hi,

C> 190 degrees is very hot. Most hydronic heating systems are run about C> 140 degrees.

Wrong as usual. most residential systems run at about 180 degrees.

C> Make sure your fan coils are clean also. I like your C> idea. You should have a ten degree difference in the temp of the C> incoming and outgoing water in the loop. I would increase the flow C> and drop the temp if it were me. This can be done with a higher C> horse motor and a fan with a higher flow rate of air. The pitch C> on the blades can increase the ccf. You'll need a different motor C> of the same rpm with at least a 1/15 hp.

All wrong. you really need to stop trying to answer these questions.

-=> HvacTech2

[Dollar_Jim]

responding to

Dollar_Jim wrote: Mark has a great point. You should have more surface area of the radiators to extract the heat. Putting a fan to distribute the heat defeats the purpose of hydronic heating system. These types of heating systems are draft free and no filters to change. Perhaps it's possible to find additional fin units.

These are easy to sweat >>

-------------------------------------

[bud--]

Mark has a great point.

Nope. Ed had a great point.

The heating unit that is the subject of the thread is a forced fan unit. Without a fan you will get minimal heat from the unit.

Your post is useless - the latest idiot from homeowners hub. And it responds to a thread that is over 7 years old. Where does homeowners hub find people so stupid?

And you are not responding to a homeowners hub thread. The thread is from a usenet newsgroup - alt.home.repair (and probably another usenet newsgroup.) Maybe you could find out what usenet is.

Homeowners' hub is a parasite that steals our work. It doesn't even attribute the source.

If you don't want to figure out usenet, I suggest using google-groups.