Hydronic heat distribution question

danskiz

Hi all,

I searched the forums but didn't find much on this. I am in the process of gut renovating my home. It is a late 60's split level with hot water baseboard. I've done a new heat loss calculation room by room, but I've run into a question I can't find much information on. Being a split level, there are basically 4 floors separated by a 1/2 story connected by 3 staircases. First is an unheated garage, then a finished basement, then living room level, and bedroom level at the top. The top floor (bedroom level) currently has all the radiators unhooked (it was the first level to get renovated). Between being significantly better insulated, and the original system oversized to begin with, It hasn't been a problem keeping the house heated, even with over a third of the original slantfin radiators unhooked. This brings me to the question.

The top floor (bedroom level) is currently staying at room temperature, or maybe just below. That is with no heaters on that level. Based on my current heat loss calculations, the Living room level has about 45% more radiation than it needs, and the Basement level has around 15% LESS than it needs.

It seems to me that since heat rises, that should factor into the distribution. Basically having the heat loss calculation for the entire house being covered, but a higher percentage of the heaters being on lower floors relative to each levels heat loss. Everything I have found on sizing heaters for a given room is based solely off the heat loss calculation for that room.

Is it not a common thing to factor in heat rising in a multi-level house when planning your heater distribution?

mattmia2

if you do the heat loss calculation correctly you are accounting for what is on the other side of the floor/ceiling/wall of that room. if the same temp is in the floor below the room there is little to no loss in that direction. the heat loss calculation is the worst case so it is likely with different weather conditions the loss on each floor will be different relative to the other floors at different times. you could calculate the ideal amount of heat to make everything even under one condition but the balance will likely change under different weather conditions. Each floor should be its own zone if you want it to be even.

danskiz

Point taken about the changing weather conditions. During the coldest winter days here, the upper level did drop in to the low 60's. The heat loss calculation is accounting for what is on the other side every wall, floor, and ceiling. It doesn't account for the chimney that is the open stairwell though. Each floor is its own zone currently. So if I'm understanding correctly, you still design room by room, but just expect that the lower floor zones are going to call for heat much more often when you are in moderate weather conditions.

HomerJSmith

@danskiz, Point of clarification, "…heat rises…". Hot air rises, heat energy travels in a straight line to what ever is coldest. Up, down, or sideways, no matter. But I know what you mean.

What is really important, I think, is that your layout is zoned and a thermostat for each zone. Then it isn't so much a problem if one zone is more or less than it needs. If you run new thermostat wire, run 3 or more 18ga conductors in a cable from the boiler to the thermostats.

EBEBRATT-Ed

Yes the "chimney effect" can't really be accounted for. I live in a small condo with baseboard. Unless the temp outside drops below 20 or so we very seldom turn on the heat upstairs (2 bedrooms and a bath). We are not up their much during the day and it seldom drops below 64 with the FF heated to 70-72.

Large open stairway between the 2 floors.

Some forget the difference between an outside wall (exposed to the outdoors) a cold partition (exposed to an unheated garage) or a warm partition, floor, ceiling or wall which is heated on the other size.

mattmia2

in theory there should be little stack effect if both levels are heated to the same temp. in practice there is infiltration out of the ceiling that pulls air through any structure, that is part of the infiltration number in the calculation. generally a different number isn't applied to different areas but i suppose you cold distribute more of it to the lower floor where air is being pulled in and less to the upper floor where already heated air is being pushed out.

danskiz

Thanks for the input. I appreciate it a lot. My plan is to keep the basement and living room level on their own zones, and split the bedroom level into two zones. The solar gain on the south side of that floor is significant in the winter so if the sun is out, it's 10 plus degrees warmer then the north side. I enjoy geeking out calculating everything out so its going to be a fun project. It looks like there's a lot of good information here.

mattmia2

be careful not to make the zones so small that they make the boiler short cycle

danskiz

I knew that could be a concern, but I honestly haven't made it to that point to research it yet (I'm learning primarily from caleffi's Idronics publications). I'm not a HVAC pro… The heat loss for that floor came in at about 16700 BTU's. If splitting that in half would cause the boiler to short cycle, maybe I could put the south side at the end of the zone to minimize the issue.