Forced hot water system w/venturii

Old 12-21-06, 07:29 AM
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Talking Forced hot water system w/venturii

Good morning to all:
My current home heating system is forced hot water with veturii.The house is 1700 sq. ft with two floors, one heating zone, thermostat downstairs. All of the rooms have radiators except for the master bedroom upstairs which has baseboard. The masterbedroom is the coldest room in the house. I have talked with several heating companies and they have told me the usual to remedy this. I have bled the air out of the baseboard. I have "felt" both pipes going to the baseboard while the furnance is running and they both get too hot to touch, but the baseboard really does not put out that much heat. One company told me that this baseboard is probably the furthest from the furnace and thermostat and never gets a chance to properly heat up. What's funny about this is the radiator on the first floor, directly below this room and baseboard throws heat no problem. Does anyone have any ideas about what else could be happening? Also.....with venturi fittings.....should they be on the inlet pipe or outlet pipe of the radiator? Thank you to anyone who can help.
Old 12-21-06, 08:12 AM
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Cold Master Bedroom

Hard to exactly pinpoint the problem from here without looking at a number of possiblities, since you state the convector pipes are gettting hot on a call for heat.

If the bedroom has been cold since the convectors were originally installed, it may point to not enough baseboard installed, or inadequate wall insulation or drafty windows.

Baseboard won't put out as much heat (or for as long) as radiators will, & the heat dissipates more quickly from baseboard, but the room should get warm nevertheless; there is also a high output version that puts out ~800 btu/hr per ft. of baseboard (standard baseboard = ~560 btu/hr per ft.).

You would have to have a heat loss calculation done for the bedroom to determine how much heat the room needs to stay warm, & then calculate how many btu/hr the available baseboard can put out by multiplying the # of baseboard feet by 560.

Some heat loss calculation sites are below.

Another possibility is the piping loop that includes the bedroom is too long for the circulator pump to adequately circulate sufficient hot water to heat the baseboard elements.

Mixing baseboard & radiators in the same piping system can often cause a mismatch in water flow; the tendency is to make the baseboard loop too long & the venturi loop can't push enough water through.

The venturi valve should be on the return leg of the convector; but in the case of low flow or indadequate output, it is common to put a venturi on both the supply & return risers; this may be one solution to your problem.

Once the cause of the problem is isolated & definitely identified, a solution can be made.

Quite often upstairs & downstairs piping loops are put on separate zone valves, using either circulators or electric zone valves; a separate thermostat can then be installed for each zone; it's possible to put only the bedroom on a separate zone, as well.

There are balancing valves that are sometimes put on the return mains near the boiler, so that the hot water flow can be more accurately controlled.

It would help if you could provide additional info as to what the contractors have suggested so far, the length of supply piping, the btu output of the boiler, the heat loss calculation of the house, the brand/model # of the circulator pump, the insulation & windows in the bedroom, &, if you have the equipment, a diagram of the piping system.

Last edited by jack horner; 12-21-06 at 08:49 AM.
Old 12-21-06, 09:51 AM
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Jack is spot on. Another thing to consider is whether the cold room has a chance to heat at all, regardless of flow, baseboard output, etc. If the thermostat is in a "warm" room, then it is being satisfied early relative to the cold room so you don't have a sufficiently long heat call to warm up the room. This would pile on to the various possibilities Jack mentioned.

Probably splitting at least that room and perhaps the whole 1st/2nd floors into their own zones would address the myriad possible issues most effectively. And definitely insulate and seal the room to get the heat loss down so whatever heat you do put in there, lasts longer.
Old 12-22-06, 10:04 AM
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May I echo the others?

Can you get the old rad back? If not, you should do room by room heatloss calculations and find out what you need to be in balance with the other rooms at your given water temperature(s). Then you'll need that much baseboard. If the baseboard is much longer than it is now you'll either have to widen the spacing between the tees or get a second venturi tee as stated. Widening is best, but not always practical.

In the opportunity corner would be getting a nice panel rad for the previously calculated room BTU requirement - you could even put a TRV on it if you wanted a bit more control over the bedroom in case you ever end up being too warm instead of too cold. The odd TRV on a diverter tee system wouldn't obstruct the flow enough to lose velocity and balance. With the panel you wouldn't have to mess with the under floor piping.

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