Hydro-Coil off of Steam Boiler

andrewd33

I am a forced air / a/c guy here and I am doing a/c in an old 3 story house with steam heat.  The house has a 250,000 BTU Weil McLain Boiler with cast iron radiators.  1 Zone.  While I am adding the a/c. (multiple systems) I recommended that we add a hydro coil to the first floor air handler so the steam would heat the 2 upper floors of the house and the condensate would heat the lower level.  His wife was thrilled because of furniture and layout etc. I am not a hydronic genious and I told the homeowner that I would provide the coil upstream of my AHU and could make the blower come on with either a time delay or an aquastat on a call for W.  Piping and all the other stuff is all to be completed by the plumber.  Currently there are only 4 radiators on the first floor that would most likely be eliminated.  Was this a good recommendation?  Any input would be appreciated since I haven't installed yet!

Dave in QCA

Horrible Idea

Here's why.  A steam boiler is carefully sized to the connected radiators.  If it is oversized, it will cause all kinds of problems and inefficiencies with the remaining steam radiators.  The pressure will build to fast, vents will sputter and spit, the burner will short cycle on pressure, etc.  The load that the hydro coild would put in the boiler would probably be about the same as the rads you plan to remove, but they probably won't run at the same time.  Plus, why would anyone want to remove comfortable radiant heat to put in drafty forced air.



The customer will NOT be happy with the finished product and you will be building a bad reputation for yourself.

gerry gill

I'm not 100% sure of what your doing,

but since you said that the first floor would now be heated by condensate, i assume that your taking a water loop off the steam boilers water chest..that could work for you if you put the rooms in question on their own zone..otherwise you will probably have wide temperature swings compared to the steam heated rooms..you'll also have to wire things so that the boiler can make hot water without steaming..this alone can be at times interesting if a drop header is not installed as that hot water in the boiler can act like gravity hot air and via convected air still heat some radiators even tho the steam t-stat isn't calling..that service call will mess with your head..another plus for drop headers..then of course like Dave said, your steam boiler will in essence be to big..

andrewd33

Okay so I got 1 for and 1 against!!!

I appreciate everyones response so far but now I have one person for and one person against the conversion.  Here is my reasoning.  We have a 3 story house here with a single zone steam boiler.  So all three levels are being controlled by one thermostat in the foyer.  My reasoning is that the first floor is going to call and end up overheating the second and third floors.  The hydro coil zone will provide a seperate zone for the first floor and let the upper floor call for steam when they need heat.  The boiler will have to be controlled with an aquastat that will call the pump to circ water on the call for heat from the hydro coil zone.  The call for W1 on the hydro coil zone will need to open the gas valve to heat the water to a max of 180 degrees.  The Aquastat on the coil will sense when the water reaches 140 and bring on the blower in the AHU.  If the upper tstat calls for heat the boiler will be allowed to make steam. 

Since I don't want to install something that will screw up the dead mens original system engineering I will write my quote to include an "optional hydro coil" .  Feasibility to be confirmed by the plumber doing the piping and water side controls.  My part will only include installing the hydro coil on the ahu and telling the blower to run when the aquastat senses heat.  If the plumber feels that this will work it is up to him to make sure the steam system will operate properly.  I don't know about this, and I am not an expert at steam and or condensate loop heating.  Thanks for your responses.

Steamhead

Now 2 against

Besides the issues already mentioned, the first floor will not be nearly as comfortable as the rest of the house. Forced-air can never equal the comfort of a well-functioning steam system. So no one will want to come downstairs.



Leave the radiators as they are. Or, you might be able to move them to accommodate the furniture.

Mike Kusiak_2

Three against

If you presently have a well running steam system, why would you want to remove the first floor radiators for other than cosmetic reasons? When the system was installed it heated the three floors evenly as one zone, so why would it not continue to do so?



If the upper floors were to overheat, you could always install TRV's on those radiators to provide individual control.



Forced air heat just doesn't provide comfort in old, poorly insulated  houses. Stick with the steam and use the forced air for a/c only.

crash2009

Lets make it four

I've read about this kind of nightmare before.  Acme Heating and Air Conditioning designs the overall project.  Farms out the steam work to Acme Plumbing instead of Acme Steam.  Acme Heating's contract says:  if anything goes wrong, blame it on Acme Plumbing.  The customer ends up here on The Wall saying "Why isn't this working?"  



Don't let the customer lead you down the garden path.  Sometimes they don't know what's good for them.  Tell the Mrs to move the furniture not the radiators.  Design the kitchen around the steam.  Move the thermostat away from the front door.