Plannersteve
New Member
I have a 5 zone hydronic heating system. The tubing is installed in a 4 inch concrete slab. My boiler is a NTI Trinity TX 51 which has a minimum heat input of 7.1 MBH. I'm in north Idaho. My total Manual J heat loss is around 25,000 Btu/hr and the heat loss for the zone in question (bathrooms) is around 2,300 Btu/hr.
During the colder months, the bathroom zone seemed to be calling for heat most of the time. Usually there was another zone coming on so the boiler ran along at some reduced firing rate. However now that we are in our shoulder season, the bathroom is often the only zone that calls for heat. What I observe is when the bathroom zone calls for heat, the boiler will run at minimum firing rate for 20 to 40 minutes before the boiler setpoint is exceeded and it shuts down. If the zone is still calling for heat, the circulating and boiler pumps will continue to run until the return water temp drops and allows the boiler to fire again. This might take 15 to 25 minutes. Then if the zone is still calling for heat, the cycle repeats.
I'm guestimating that this cycle might occur 6 to 9 times a day during the shoulder season. Is that amount of cycling acceptable?
I believe the root cause is that the heat transfer surface from that zone is too small compared to minimum boiler fire rate. I've raised this as an issue with my installer. Obviously adding more tubing to the concrete is not an option. My thought is we would need to add some heat transfer in the bathroom. One idea is to add a large towel warmer. Or a radiant panel. My thought is to propose that my contractor share in the cost of this, but again I'd like some experienced folks opinion on whether or not this is really a problem.
I've set the CH setpoint differential at 14 degrees, so the boiler will operate longer before shutting down for high temp. I could go higher, but not sure of consequences other than reducing the boiler efficiency some. There may be other control solutions which I'd welcome.
During the colder months, the bathroom zone seemed to be calling for heat most of the time. Usually there was another zone coming on so the boiler ran along at some reduced firing rate. However now that we are in our shoulder season, the bathroom is often the only zone that calls for heat. What I observe is when the bathroom zone calls for heat, the boiler will run at minimum firing rate for 20 to 40 minutes before the boiler setpoint is exceeded and it shuts down. If the zone is still calling for heat, the circulating and boiler pumps will continue to run until the return water temp drops and allows the boiler to fire again. This might take 15 to 25 minutes. Then if the zone is still calling for heat, the cycle repeats.
I'm guestimating that this cycle might occur 6 to 9 times a day during the shoulder season. Is that amount of cycling acceptable?
I believe the root cause is that the heat transfer surface from that zone is too small compared to minimum boiler fire rate. I've raised this as an issue with my installer. Obviously adding more tubing to the concrete is not an option. My thought is we would need to add some heat transfer in the bathroom. One idea is to add a large towel warmer. Or a radiant panel. My thought is to propose that my contractor share in the cost of this, but again I'd like some experienced folks opinion on whether or not this is really a problem.
I've set the CH setpoint differential at 14 degrees, so the boiler will operate longer before shutting down for high temp. I could go higher, but not sure of consequences other than reducing the boiler efficiency some. There may be other control solutions which I'd welcome.
