Help w/ piping to hyrdoheat hydronic aquatherm First Co combo heater

[ITSec]

I had an Apollo water heater that died on me over the holiday. The Apollo water heater had 4 ports, 2 for domestic water and 2 for the air handler in the attic. I assumed the only way to heat my house was to purchase another Apollo water heater, but I was wrong. In a earlier thread I noticied a regular water heater connected to the First Company AquaTherm heating system by "T" fittings on the vertical hot and cold water supply lines at the water heater. So it looks like I can regain the central heating in the house. This is where I need the help:

How should I pipe to the air handler?

Can I use PEX, CPVC, gatorbite/sharkbite?

Thanks in advance for your help!

Picture of flex lines going into water heater


Picture of lines going to air handler


The return line from air handler


Check valve that was on the supply line to air handler

[Dana]

PEX would be fine- most is rated up to 180F (and can actually tolerate extended use at 200F, but nobody rates it there.)

Even though your new burner is lower output than the previous version it should still work OK with the air handler. Start by setting up the tank for 140F and measure the temp of the return water. As long as it's above 125F it probably won't be condensing (much), but you may need to bump the tank temp even further to achieve that.

If the coil in the air handler proves to be so big that even at 150F storage temp the return water temps are too low, plumb in a "boiler bypass" loop with a ball valve on it to mix in some water from the hot supply into the return water from the air handler before it goes back into the HW tank. You can then adjust the temp of the water entering the tank by the amount of bypass flow. Whether the pump is driving toward the air handler or whether it's driving toward the water heater, as long as it isn't between the bypass loop and the air handler coil you'll still be able to get the full output of the burner into the coil. (If the pump is internal to the air handler unit, as is likely, there may be some dissection involved.)

[ITSec]

The original water heater was rated at 65,000 BTUs, the new one is 40,000 BTUs, it should still be enough to heat the house. I did a rough calculation for heat loss and multiplied it by 1.58 and it was under 40k BTUs. The calculation was from the first co website.

I'm thinking about returning the WH if I can, and purchase the ao smith with the ports on the side. It's becoming a PITA trying to figure out how to connect everything using t fittings. Gator bites aren't cheap, neither is pex and I think I need a crimper. Might have to get some scrap pieces of copper tubes and practice how to solder.

[Dana]

My antique ~2200' + 1500' semi-conditioned basement house in central MA is under 40K for a heat load @ 0F outdoor temps, so the odds you'd just fine with 40K of burner, but going with the condensing Vertex with the 76K burner would be a big step up in efficiency, and the lower the return water temps, the better the efficiency. They're a hunk of change (~$1.5KUSD), but the better efficiency should pay for the difference over a handful of heating seasons, after which it's all gravy.

[ITSec]

Thanks for all your help Dana! I finally have heat in the house, not fun getting ready for work when the temp in the house is 58F. From the vents I'm getting 109F, but when the shower was running dropped to 88F so I turned off the central heat until the water heater could catch up. I have attached a pic of the slice and dice of the copper lines with shark bites and CPVC. I know if a pro plumber sees this, they are going to say WTF.

My butcher job of the copper pipes.

[ITSec]

Dana,

Will an aquastat help in my situation, since it's getting colder outside the air handler and water heater runs 8-9 hours a day. When the heat for the house kicks on, the air coming through the vents is hot for about 30-45 mins then the air begins to cool down to a point where it doesn't seem to heat the house anymore. When this happens I turn off the heat and wait for the burner in the water heater to turn off, then I turn the heat to the house back on. I think I'm going to kill the water heater since it seems like it's running all day long. I currently have the water temp set at 140 F.


A quote from Dana in another thread.
By setting the tank temp high and using an aquastat on the air handler to cut power the blower whenever the exit temp drops below 125F you can save the HW heater, and keep the air handler from robbing too much from the showering performance.

[Dana]

"65,000 BTUs, the new one is 40,000 BTU".

It's no longer balanced as a system they way it was originally designed, now that the heat input has dropped ~40%. It's enough burner to heat the house, but the coil in the air handler gets ahead of the burner, and the temperature of the tank drops. Installing an aquastat that cuts out the power to the blower (but not the pump) when the return water coming back from the coil is under 125F would cycle the air handler on & off with some hysteresis while the burner runs continuously. If the burner is perfectly-sized for the heating load it SHOULD be running a high duty cycle during the colder hours. It's fine for the burner to run all day long, as long as it's not condensing in the flue (which WILL happen if you run it when the tank runs cold.)

Some First air handler blower motors have strappable windings for different blower speed (mine does). If yours can be wired to run at a slower speed it'll blow warmer but more gently, and will likely work better with the lower-output burner.

[ITSec]

I actually have a video of what you described, water droplets were falling onto the burner from the flue. This only happened once when I first installed the water heater, it was probably 50F outside when this happened. It's been 30-40F lately and I haven't seen this problem come back.

[Dana]

The outdoor temp doesn't much affect the problem- it's the tank temperature that counts. When the tank is stone-cold (<<100F) on startup this condition is "normal" until the tank gets closer to domestic hot water temp.

If you let the air handler run until the tank drops to well under 110F it could actively drip like that. But corrosive condensation can occur at higher temps even without it dripping at the burner. Exactly where the crossover temp is will depend on the particular tank design and the pumping-rate/turbulence in the tank, the return water temps, etc. With return water at 120-125F it should be pretty safe from condensation. At 100F not so much. The delta-T on the coil is likely to be something like 20F (140F in, 120F out) or even 25F, and it may be worth bumping the temp (and installing an aquastat with ~10F of hysteresis to cut out the blower at temps in the 120-125F range, turning it on when return temps hit 130F+) if return water temps are much lower than 120. You'll have to play around with it and measure the actual temps to tweak it in.

With tight, insulated ducts and 130F entering water at the coil the exit air at the registers will still feel warm (higher than body temperature), but even with 120F water and a tepid 95F exit air it'll still be heating the house, but won't feel so cozy in the draft next to the register, but the return water temps will likely be a condensing 110F or lower when that's happening.

As a strategy to keep that from happening before adding aquastat controls, bump the tank temp up to 145-150F, and keep the room thermostats constant (no setback), so there are no long recovery ramps from setback. Odds are that most of the time with normal thermostat hyseresis it won't have to run more than 15 minutes before the thermostat turns off the air handler & pump. At 140F entering water temp the air handler is probably taking ~45-50KBTU/hr out of the tank, but the burner is only supplying (0.8 x 40K=) 32K/hr, or about a 12-15K shortfall. A 40 gallon (335lbs of water) tank dropping 20F degrees is 335 x 20 = 6700 BTUs of heat stored in the water, which at a 15KBTU/hr shortfall would take (6700/15000=) 0.45 hours, or 27 minutes.

If you add an aquastat with ~10F of hysteresis to interrupt the blower it will be cycling the air handler something like ~12 minutes on, ~5 minutes off until the thermostat is satisfied during situations like setback recovery or design-condition outdoor temps. Something like the ~ $50-60 Johnson Controls A19DAC1C available from multiple web vendors should get you there with a simple strap-on connection to the return line from the coil (no plumbing required), with current ratings appropriate for air handler motors. (Be sure to wire it for make-on-rise.)

In the longer term when it's time to replace the tank, a condensing tank with a bit more burner behind it would make the whole headache go away, and you can run the tank at a lower temp for higher condensing efficiency and lower standby loss. The 76K burner on the Vertex would deliver ~68K or more in condensing mode, whereas the original 65K burner was only delivering 52K. If you set the tank to 125-130F the return water would always be in the condensing range for 90%+ efficiency, but the exit air temps will be lower at the registers. If the exit air temp is uncomfortably low you can bump up the temp of the tank a few degrees at a time, but know that the combustion efficiency will be dropping and standby loss increasing with higher temp.

[ITSec]

I just had an idea! I was thinking of a way to make my system more efficient since the return water from the air handler is coming back cooler. So here's my idea: I was thinking of a way to wrap the copper line from the air handler around the flue. In theory when the water heater is on, the heat from the flue will heat the return water a few degrees warmer. The IR thermometer showed 120 - 140F on the outside of flue and over 200+F on the inside. This idea is similiar to the Shower Drain Water Heat Recovery. Any thoughts?

[jadnashua]

You'd probably not get great heat transfer, but keep in mind that if you cool the flue gasses off too much, you get condensation and rust the flue out very quickly.

[ITSec]

Water going to the air handler is about 140F the return water I estimate 120F.

Nevermind, in my brain I thought this was a good idea. Guess I need to take off my plumber's hat and put my IT hat back on.

[Dana]

Stack economizers take real design- hacks are always expensive underperformers. An already-engineered condensing HW heater would be cheaper & more reliable (and comes with a warranty.)