Air Handling Unit

dbrewer

I have a residential air handling unit that provides home heat and hot water. In the spring, we noticed that our air conditioning in the house was not functioning properly. An expert adjusted the speed of the Handling unit. Now that it is winter, we have noticed that the home heat works, but the hot water will not work unless the air handling unit is running. If I turn up the thermostat and the unit turns on, the water will go from cold to hot. Do I need to adjust the speed setting of the air handling unit in different seasons? Thank you.

dbrewer

Any help would be much appreciated

pecmsg

A/C requires 1 speed.....Heating another. There are ways of doing this automatically. Get the expert back to fix it!

dbrewer

I will. do you know if heat or a/c requires being at a higher or lower speed? ie. in winter, should i be reducing or increasing the speed. Are hvac people quite familiar with air handler/hot water systems? I'd never heard of it, but bought a new house with it already installed.

pecmsg

Heating lower speed. A/C higher

He needs to measure the static pressure and temperature rise / fall

dbrewer

thank you so much.

Jolly Bodger

@dbrewer Can you post some pictures of the system? What make and model is it? Did the hot water work over the summer? If I am reading this correctly you said that you only have hot water when the unit is heating the house. And cold water when the unit is not heating the house?
pecmsg is right about the speeds, but if that was causing the cold water seems to me like it should be the other way around. Cold water when the unit is heating the house.

dbrewer

Yes the hot water worked fine. We moved into the home in February 2019. All was fine in the cold weather from feb to May. Then when the a/c kicked in in June, we noticed the house was not cooling(the hot water was fine all through the summer). When the hvac guy adjusted the speed to fix the air, everything worked fine until about 3 weeks ago(I assume this is when more heating was being used in the house). At this point the hot water stopped working, but only when the air handler unit is not running. As soon as we turn up the house thermostat to kick in the heating, the water goes hot. So, it seems that when the home heating isn’t running, the hot water no longer kicks in.

pecmsg

Are you heating and cooling with the water or is it part of a water cooled system?

dbrewer

It’s an air handler connected to the tankless water heater.

Jolly Bodger

It is not the speed of the air handler. There is some other failure. Your tankless unit is not seeing flow unless the pump for the air handler is running. We will need to see pictures of the setup to tell what is going on.

dbrewer

This is how the settings were during the summer when everything worked fine. Any idea how they should be adjusted. There appears to be 3 adjustments. One for heat, one for cool and one for fan.

dbrewer

These r photos from the tankless to the air handler unit

Jolly Bodger

I suspect there is a check valve stuck open between the air handler and the water heater. it could be in the air handler, or in the pump in the air handler, or in the mess of PEX near the access hatch. It is hard to see what is there. What is likely happening is when you open the hot water tap the water flows backward from the cold line through the air handler and back to the hot lines to the house. A good HVAC guy will be able to find the short circuit.
It's a new issue. Not the fan speed. Don't touch that fan speed.

dbrewer

Ok sounds good. I’ll bring the pro back in. I get the impression these aren’t very common systems. It’s hard to find much info online.

Jolly Bodger

I wouldn't call it main stream. I have mostly seen them in condos.