Is oversizing heat circulator pump ok?
Hi,
I have a 2400sf house that is heated by forced hot water, 2 zones. I want to change the setup such that the family room on the back side of the house is on its own zone since it tends to be cooler than the rest of the house due to air infiltration and the massive fireplace. Since we spend the most amount of time here, it make sense to have it on its own zone.
The company who installed my AC system wants ~$1400 to do this. I hoping to save some of the cost by buying some of the parts (e.g, new Taco zone control relay, heat circulator pump, thermostat) myself, doing the electrical work, and then having my plumber do the piping work.
The system currently has 2 Taco 007 F5 pumps. My thought was to just buy another one of those. Is this ok? Or should I let my plumber do the sizing calculations and get the right sized pump which would likely be smaller. I understand that you don’t want to undersize the pump but is oversizing an issue?
Replies
yes, turn on your vacuum cleaner, restrict the flow and listen to the motor start to strain. The pump should be right sized to avoid premature failure and to operate at peak efficiency.
The motor actually uses less current with the flow restricted than it does full open. It's doing less work with the flow restricted. What you are hearing is the change in air flow, not the motor. A dead headed circulator will draw minimal current. Both the vacuum and the circulator might overheat eventually but that's a different problem.
Oversizing a circulator is just a waste of power, which adds up.
"With every mistake we must surely be learning"
Oversizing the pump will erode the pipe if its metallic
Oversizing the pump is not good. One, you pay (most likely) more for the pump than you need to, and two, you have the great potential of creating a noisy cluster. Sizing the pump is one, and only one, part of the equation.
I would recommend you do some research to find out how your system is piped, how it is zoned and how the zones are controlled and/or actuated, how big is the zone that presently heats the room you want to zone separately, how much heat does that room, how big will the remaining zone be when this alteration is complete, how will that affect its operation and/or control, how is the boiler protected from shock and condensation, how is the water temperature controlled, etc., and a few dozen more questions you need to answer. If you really want to DIY this, you have some reading and learning to do. It is not rocket science and is easily a DIY project for a lot of competent non-tradespeople.
OTH, you may want to consider just hiring a hydronic heating professional to do the whole job. That may or may not be the people that installed your AC (most likley not) and it may or may not be your plumber. There are lots of knowledgable hydronics pro's in your area. Check out HeatingHelp.com
Edited 7/24/2006 2:06 pm by Tim
Hi Tim,
Thanks for the response. The reason for my asking the question was to see if I could save a few bucks by ordering some of the parts myself (e.g, zone controller & circulator pump), doing the electrical work myself (e.g, zone controller & thermostat) and having my plumber do the rest. The AC vendor is an hvac shop and will do boiler installations, etc so they are qualified to do the work. But they're a larger shop and have more overhead. I don't think their price ($1400) is outrageous based on the work that needs to be done (change zone controller from 2 zone to 4 or more zones, wire thermostat, new circulator pump, labor, etc).
From my perspective, $1400 is a lot of dough just to make one room a bit more comfortable. If I could bring that cost down closer to $700, it would be more appealing to me. I was thinking of getting the zone controller (6 zone) and the pump on Ebay but now, I think I will just get the zone controller and let my plumber deal with the pump.
It's difficult to figure out the heating pipe arrangement on my system because the basement ceiling is all plastered. The boiler is a Weil-McLain CGA-5 Gold. It has 2 zones, 1" supply/return pipes, 3/4" pipes to all base board radiators. I believe it's a split system in that it splits off into 2 loops for the downstairs and probably 2 loops for the upstairs. Last winter, I had the downstairs heating pipe freeze because it was a very cold day and we were using the woodstove thereby causing the heating loop to not circulate for a long time. The entire downstairs was not getting heat except for the living room. So it seems that the living room is on one loop and the rest of the downstairs (hallway, dining room, kitchen, and family room) were on the other loop.
How does one figure out the system is piped if they're all hidden?
I spent some time last night perusing heatinghelp.com. I had seen this site before but didn't really browse it much. There's definitely a wealth of information, especially under "Hot Tech Topics".
There's one that's a bullseye for me. "How to size Circulators" http://www.heatinghelp.com/newsletter.cfm?Id=161
It describes a simple formula for determining the flow rate and head pressure for a pump based on the pipe size & length. Cool stuff.
A Weil-McLain CGA is a cast iron gravity vented natural gas boiler. Pretty vanilla, so we can make some safe assumptions: The system is probably designed for 180 degree supply and 20 degree temperature drop, or something very close to this. It doesn't really matter, so long as the heat emitter you select is big enough for 180 degree inlet. If its hotter than that, that's ok.
Where the pipes are exposed, like as in the basement where the boiler is located, you can tell if it is piped in a primary/secondary, a series or an injection type of configuration (or possible some combination of various types). If there is a complete loop out of the boiler, including an air separator/expansion tank/boiler feed-prv assemby, then a circulator pump and branch connections for each of the zones, and back into the boiler, then it has a primary/secondary loop. If it has this type of arrangement, but with supply and return tees right next to each other (i.e. closely spaced) and maybe local zone circulator out in the house, then it is what I call an "injection" arrangement. If one pie goes out and goes into and out of every radiator/baseboard in the house, then it is a simple series arrangement, even if it is split between two floors. These are very simplistic explanations, but hit the basics. Based on what you've describe so far, I don't think that you have a series type of system.
Zoning with circulators is pretty simple. The boiler is set to maintain a supply temp and controlled internally, and either "always on" with the boiler circ running constantly or fires and circulates on a "call for heat" from the zone control panel(s). I always keep all pumps and panels near the boiler in plain sight, but not all are done that way.
To add a pumped zone, you need three things, other than a heat emitter (radiator, basboard, convector, etc) and pipes to and fro; a pump, a thermostat and a means to start the pump (AND the boiler if necessary).
For the pump, I would recommend the Grundfos 120v UPS15-58FC. This is a 3 speed pump with a built-in check valve. The 3-speeds give you the flexibility of one a single pump that will match a fair amount of residential zones, and then selecting the correct pump is easy. BTW, it cost the same withing a few$ as a single speed cast iron circulator.
The thermostat can be line (120 VAC)) voltage or low (24 VAC), depending on other controls. With a control panel or switching relay, you use low voltage and let the relay(s) start the zone circulator and if necessary, send an isolated call for heat (TT terminal on the switching/zone relay) to the boiler. If the boiler is "always on" you can go line voltage and let the t-stat start and stop the pump as the space demands, a very simle arrangement, except you have to run the hot leg for the pump power to and fro the t-stat. I prefer the switching relay option except for the simplest, single zone systems. Whether you have an integrated panel that combines many switching relays into one box or not, does not matter, they all work the same.
IF you need to signal the boiler and start the pump as well as provide a 24VAC signal to the t-stat, then the switching relay and/or zone (circ) panel is the way to go. The pump and the panel are all wired locally (in the boiler area) ad only a 2-wire thermostat wire has to be run to the t-stat. For the relay, I like the Honeywell R8845U http://customer.honeywell.com/honeywell/ProductInfo.aspx/R8845U1003
If the boiler is piped with a main loop and closely spaced tees, then your new zone will duplicate that piping arrangement. If there is a supply "header" and a return "header" then you will duplicate that arrangement. If you can sweat pipe you can add a zone.
Edited 7/26/2006 12:52 pm by Tim
I had my plumber stop by last week to look over the job and to give me an estimate. He spent about 3 hours looking over a few things that I wanted to do as well as talking about his work which I always find fascinating.
He discovered that there is a T in the supply line to the family room and recommends that we use zone valves instead of adding another circulator line. This would minimize the amount of additional piping that would need to be done thereby reducing the overall cost.
Sounds like a good plan. Now I just have to wait for him to call back with the estimate.
Adding zone valves to areas of different use will certainly benefit you in that a more custom level of comfort can be maintabed and in not heating areas used infrequently, have the potential to save some (but not much realistically) energy.
Hope that it all works out the way you hope.