Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Gravity Conversion Questions

First I want to thank everyone for the help you gave me getting my steam system in VT running smoothly. I got it working on 1/2 psi. I've moved south and now have a project in a house that has a large gravity hot water system converted in the 1960s with a 1991, 180k Smith boiler. The house is 1902 vintage approx 4000 sq feet with standing radiators and indirect radiator in entry/stair hall, 3 floors plus basement. There is a sunroom with copper fin that is being replaced by CI baseboard. The third floor is currently heated by electric baseboard. Original gauges and 1888 powers damper control ( inactive) still in place. B&G 100 circ. No bypass, 6" diameter mains near boiler. There is a existing staple up radiant zone in the kitchen and that is largely ineffective. Location is in KY, but we have a relatively high local power rate of 15 cents kilowatt/hr. The current control strategy is Honeywell round thermostat starts pump and burner. The limit switch control failed and I want to upgrade controls. Additionally I would to add heating to the third floor in the future--possibly using the fin tube removed from the sun room. There are very few wet heads here that can assist.

1. What would the best control strategy given the cost of electricity and multiple temp zones?

2. Would it be simpler to use CI base on third floor.

3. The radiant zone uses a modular zone control panel and mixing valve connected to 3/4" pex tubing in joist bay with foil wrap insulation below. It diverts water off the stub outs to the original kitchen radiator. Kitchen cannot maintain 63 degrees on most winter days, could this have ever worked? Installed by previous owner (along with the fin tube).

4. The sun room is the main entrance from garage, has two exposed sides (9540 btu heat loss) and is open to kitchen and a stair hall, would it be better on its own zone?

Thanks in advance. Chris in Kentucky.


  • SWEI
    SWEI Member Posts: 7,356
    As per usual, start with a room-by-room heat loss calculation and radiation survey. Once you have that, you can choose new emitters which most closely match the performance of the existing ones. In the event that is not practical, you can create a new zone with its own ODR curve. Individual overheated rooms (especially those with winter solar gain, solid fuel stoves, or cook heat) will benefit from TRV's.

    One ODR curve comes for free with every mod/con boiler. Current Viessmann boilers manage two. There's an add-on module for three from Lochinvar. Taco iSeries-R valves can be added to anything.
  • Ironman
    Ironman Member Posts: 6,686
    As SWEI pointed out, you need to use emitters that match the performance of the existing CI rads. That means high mass. The fin tube is low mass and even though you may size it large enough to match the heat loss, it will not perform like the CI rads and you'll have a large temp swing wherever you try to use it. The same goes for the radiant floor which was incorrectly done.
    I don't know if you're trying to keep the existing boiler or if you're open to installing a mod/con, but you'll need to create at least two, maybe three, temp zones as SWEI has said. It don't think that's very practical, though it can be done, with your 23 year old boiler.
    Installing a mod/con that can do multiple temp zones would be your best investment if you can afford to do so.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • ChristopherJ
    ChristopherJ Member Posts: 6
    Thanks everyone,
    I've ordered cast iron baseboard for the missing sun room radiators, so that the mass is closer to the existing radiators. I'm trying to keep the boiler running until it can be replaced, but need to replace the boiler control as it has quit working. I would like outdoor reset to save energy. In trying to hedge my bets, would something like a Tekmar House Control be an appropriate replacement control, and should i investigate repiping the existing boiler to p/s or injection mixing? The radiant floor zone was done by a previous Owner and may not be worth salvaging. The third floor is one large open room that is not used continuously and my thought was to give it its oven zone and circulator so that the lighter mass copper fin tube would not be on the same zone as the cast Iron. I'll post pictures this afternoon.

  • Paul48
    Paul48 Member Posts: 4,470
    What wass the result of the heat loss for the sunroom?
  • icesailor
    icesailor Member Posts: 7,265
    I'd really look at a Taco "I" Series 4 way valve for the gravity part. You get all that you want. The I Series valve takes the place of a partial P/S system, and you maintain the higher temperature on the primary side, the ODR controlled on the secondary side. You can do whatever you want on the other sides. You'll need hotter temperatures on the radiant mixer to get it to work. You will still have your high mass boiler. If you go to a beer cooler boiler on the wall, you will run into all kinds of unintended consequences from a lack of available hot water. Those "I" Series 4-ways really are the nuts in a situation like yours.