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I have a hot water system with no circulator pump


Its a 110 year old house, attached brick in Brooklyn NY. 2 stories. 20x55. 11 rooms, 10 radiators. Gas fired furnace. Used to be a steam system, but was converted to hot water, probably about 25 years ago, and supply and return lines are I think 3 inches. 2 separate closed loops, (one with the front radiators and one with the back radiators). Furnace towards the front in the basement.

This system has no circulator pump to move the hot water around, and thus the radiators on the rear loop, especially on the 2nd floor, tend not to get hot so easily, or stay hot for very long. I am sure a circulator pump will address this problem, but I still have a couple questions:
1 - At over $1000 installation, is it really worth it to install? I spend maybe about $1000 +/- all winter heating my house; If I want this investment to pay for itself in about 5 years or so, it would need to increase my efficiency a good 20%, no? Can I expect that?

2 - Contractor also offered to connect the 2 loops, so the pump would circulate through both of them. Do you think this is a good idea? We have no issues at all with the front loop, on either floor, so my feeling is that having the pump address BOTH loops would decrease its effectiveness.

Any insight appreciated, and many thanks

Re: I have a hot water system with no circulator pump

You are right to have misgivings about adding a circulator to your present system, as there are a number of issues involved that have to be addressed before you do.

Most people in the heating industry regard a HW gravity system as a dinosaur & recommend scrapping the entire piping distribution system in favor of small diameter pipes that deliver pumped FHW to the rads efficiently---an exception is perhaps Dan Holohan, the owner of the "heating help" site, listed below.

First, read up on gravity systems with Holohan's article; once at the site, click onto "systems", then onto "hot water" then onto "gravity hot water heating"----the article is long & intricate, has a lot of ideas about troubleshooting the system to get a better performance before deciding if a circulator is the best way to go.

The first step is to review how gravity heat delivers the heat to the rads by lightening the density of heated water, which allows it to rise in the piping system to the very top.

Very important, is to follow the instructions in the article to bleed the rads, starting at the bottom floor & work your way up to the top floor, so that all the air is removed---the uneven heat you are experiencing may simply be air trapped in some of the rads.

I would say that if you have 2200 sq.ft. to heat & you are paying only $1k in gas expense per season, you are doing well---you have a boiler there, not a furnace; what size is the boiler & how old is it??? ---there is usually a nameplate somewhere on there that has the output listed in thousands of BTUs/hour.

Do you have adequate insulation in the exterior walls & attic (R19 and R40 recommended); since there is between 50 to 100 gallons of water in a gravity system (modern FHW systems have 14 gal)---heating this amount of water is often very costly; a bypass pipe at the boiler piping is almost always recommended for these systems if a circulator is installed to prevent thermal shock by introducing cold water into the combustion chamber metal parts.

Gravity systems are typically hard to balance for even heat; this is often due to pitting on the interior walls of the piping, & iron oxide sludge (black gooey stuff) that can block water flow at the fittings, as well as air entrapment, as noted above.

If troubleshooting methods don't work, Holohan offers some suggestions for modifying the near-boiler piping by reducing its diameter, and adding a series 100 circulator by B&G (Bell & Gossett) to get high water flow with relatively low head pressure.

Also important to get the right people in there to work on your system---very few heating techs have ever even heard of or seen a gravity system & can make matters a lot worse by randomly adding a circulator without making the additional changes recommended by Holohan.

Check the Yellow Pages under "Heating Equipment" and go to your local heating parts supply house & ask the counterman to recommend a hydronic tech who is familiar with gravity HW systems, and has been around for a long time & knows his stuff---usually, the older the guy is, the better---these heating supply houses usually know most of the hydronic techs & deal with them on a daily basis.

Holohan, btw, is based on L.I. at Bethpage; it's a good idea to also enter your request for info at his forum (called "The Wall", or "The Main Wall"); click onto "Ask Questions" when you get to the site, then onto the "Main Wall"---this site is dedicated almost exclusively to HW heating & is frequented by numerous hydronic techs throughout the U.S., mostly the Northeast.

At the Old House Journal site, click onto "Archives", then onto "HVAC & Insulation" then onto "Cool Ways to Heat Old House" for an article by Holohan on adding a circulator for constant circulation during the heating season, adding outdoor thermostat reset (ODR), & running the system as a radiant heat source with a Mod-Com boiler---these are interesting concepts; since radiant heat is based on injecting large quantities of heat BTUs into objects, the idea is to inject lge quantities of heat BTUs into the lge number of gallons of water in a gravity system & release them constantly at lower temperatures (120 degrees) than the standard 180 degrees used in older HW systems.

If you want to check additional resources, click onto my name & leave a PM with a web-site address.


Re: I have a hot water system with no circulator pump

Nashua, Thanks for a great link to gravity systems.

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