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The house needed a mod/con boiler, domestic hot water, a hot water air handler with A/C and a couple of zones of in-floor heating. There are two temperatures required for the in-floor heating, one for the air handler and one for the indirect water heater. The house is about 4,000 sq. ft., and there are four bathrooms. The master bath has a multi-head shower (6.5 gpm) plus an 80 gallon soaker tub. The other three bathrooms have a standard tub and shower combo (1.75 gpm each). The heat loss for the house is about 118,000 BTUH.

You choose a mod/con boiler with a net output of 146,000 BTUH and a 40 gallon indirect water heater. You opt to build the primary loop. Since the boiler has 1” connections you make the primary loop with 1” connections and start adding the four zones required. You decide on a manufacturer-built P/S “T” to make the install faster. Once up and running, the owner says the in-floor is not working properly and the DHW doesn’t recover as fast as he expected.

BASED ON THIS INFORMATION:

1. Based on the net input of the boiler and assuming a 20°F delta T, the primary loop should be:

1. 1” just like the boiler connections.
2. After “doing the math” you should have used 1-1/4”.
3. 1-1/2” worked on the last job, should have used it here.
4. It doesn’t matter because it is a modulating boiler, and the boiler will adjust the flow internally, right

2. You are not sure why the DHW can’t keep up. The literature says you get 132 gallons per hour. That should be more than enough hot water. You used a priority zoning panel and the boiler goes to high-fire for domestic hot water calls. The indirect connections are 3/4” and that is what you used to connect from the primary loop. You “do the math” and discover that the total flow could be:

1. 5 gpm
2. About 12 gpm
3. It doesn’t matter, I have used this system on lots of jobs and it always works.
4. You must have a bad indirect. Take it back to the wholesaler and get a new one.
5. I will just put a flow restrictor on the roman tub filler, and slow the flow down.

3. The owner complains that sometimes the air handler blows cooler air. Not all the time, just when it starts to get much colder. You look at the piping and decide you should have:

1. Prioritized the air handler so the in-floor shuts off when the air handler is running.
2. Just turned the system temperature up when it got cold.
3. Put the high temperature load first.
4. Walked away. You can’t help this customer, he is just a complainer.

4. The proper way to do this job would be to:

1. Take some basic hydronic training from manufacturers or trade associations.
2. Use a pre-built hydronic system using a low-loss header with pumping modules so that it is just plug and play and repeatable.
3. Follow the instructions.
4. All of the above!