Heating options for radiant flooring
Michigankayaker
| Posted in Energy, Heating & Insulation on
I have a 7 year old house with a radiant heating system on the lower level (forced air throughout). My 75 gallon closed system water heater, which supplies hot water for the entire house and the hot water for the radiant floor has been a disaster; the gas valve and blower need to be replaced and I am currently without hot water. The plumber has indicated that there have been constant problems with this particular AO Smith GPDX water heater. I am faced with repairing it for $600. – $800. with no guarantees that more problems won’t occur, replacing it for approximately $3500 – $4,000, or installing a boiler system for $7000. – $9,000. I would like some advice on these options or any thoughts on options I may have overlooked.
Replies
Why does
replacing it cost $3500--4000? That sounds like a helluva water heater.
Assuming that you have natural gas and it's cheaper per BTU than electric, a gas boiler is the usual choice for running a radiant floor. You can use the same boiler for indirectly heating your hot water, without mixing the floor water and the drinking water.
If you really want to go for it, you can install an air-to-water heat pump like a Daikin Altherma. That will be more than the boiler cost, but it will use a lot less energy to produce the same amount of heat. They work great in our moderate climate, but you would have to find out what works in yours.
radiant floor heating
Thanks for your reply. In regard to the replacement cost of the water heater, the unit itself is a dual unit 75 gallon heater direct vent which costs around $2500. I'm not sure what explains the difference between the unit cost and the plumber's original estimate. He may have thought we needed to replumb the system for this water heater. Beyond cost, an issue is reliability. We have consistently heard that the newer water heaters are not holding up over time due to all the new federal requirements that have resulted in redesigns.
We have friends who have put in two separate gas water heaters: one to heat their regular house water and the other for the radiant flooring. Our plumber has said that using a water heater that is not specifically rated for radiant heating would void the warranty. However, this seems to be the least expensive option. Both friends have had their systems for 10 years without problems.
Our plumber has recommended a Knight boiler as the most trouble-free, long-term solution. However, the initial cost and the ongoing maintenance costs seem extremely high. We only have the radiant heat in the lower level of our house which we use occasionally and could supplement or replace the heat with our whole house forced air system. (We put the radiant heat in for additional comfort.) We obviously still want to use the system, but don't want to invest a fortune in it.
I'd appreciate any added insight on this problem. For the short term we had the plumber install a used electric water unit to take care of our house needs (the radiant heating is disconnected).
Water heaters
Due to fuel costs here, electric heat and hot water are usually the best choice. In rare occasions when I have to deal with a gas water heater, I don't want to install a natural draft unit UNLESS the location it's in has plenty of combustion air. If your install location is a closet or small room inside the house, I would probably invest in a direct vent unit. If your install location is a large, semi-conditioned basement or better yet a garage, it might be OK to go with a natural draft unit. Whoever is installing it needs to understand combustion air. Best case, you install 1-2 low priced gas heaters ($300-500 each), worst case you need a boiler with indirect water heating, or even a boiler and a separate water heater. If you get a boiler, choice is usually driven by your choice of installer/service tech. The guy I hire, he has 30 years experience and installs what he wants to.
Hard to say what a boiler should cost you. Only way to find out is get bids. My guy changed out a funky older unit for a new Triangle Tube unit with indirect hot water, including a bunch of repiping in the boiler room, new flue, etc. etc., about $9000. Ongoing costs expected to be extremely low. On another job, replace old gas water heaters with one electric boiler and one electric heater, $4500.
Options
First, I recommend paying a reputable AO Smith dealer/installer to repair the unit. By reputable, I mean one that will guaranteee their work. By the numbers you posted, you could pay for 10 or more repairs before you approach the cost of replacing the entire system. This would be the best use of you cash, given the situation as it is.
IF this doesn't work, I recommend separating the DHW from the supplemental space heating (this for a basement only, correct?). Two smaller units should provide all you'll need at a fraction of the cost of the whamadyne-combo-cluster thing installed.