Hydronic Furnace

I ran into a Hydronic furnace system the other day that had been designed for use with a 40 gal LP gas water heater. The owner had removed the LP gas heater and replaced it with a 40 gal electric(in order to save money). The new system had not yet been used through an entire winter. I admit to being weak in my knowledge of this type of system.
I expressed concerns that the new system might not operate as designed knowing that an electric heater does not have the recovery rate of an LP heater. Of course, I defaulted to the experts and recommended they bring in a Heat/Air guy qualified in this type of system for his advise. I did also advise the Realtor(verbally) to google it for general info and to call the factory and talk to the experts, since he expressed to me a complete lack of knowledge in this area.
I am aware now that this killed the deal.
Anyone have any thoughts on my call?

I too would have been concerned enough about the systems recovery rate to have recommended that the buyer get specialist advise.



Sounds like referring it out was the prudent thing to do because the owner modified the system without knowing what he was doing apparently or whether it would work properly after the modification.

The owner killed his own deal you just reported the system. I wonder if he is happy with the money he saved?

Ya, a 40 gallon electric will not put out near as much heat as the 40 gallon gas.

You did the right thing.

It’s all about the recovery rate and a standard electric 40 gallon just can’t keep up with a 40 gallon LP unit.

I am not a hydronics expert but, as an engineer, I have often had to calculate differences among available energy sources to determine which energy source would be the most economical. Every situation is different but electrical hydronic systems are often the most economical.

As for the question of recovery time, it is not likely that recovery time is going to be much of a challenge to any heating system. Assuming a municipal water temperature of approximately 50°-55°F, a general purpose water heater typically needs to raise the temperature 65°-85°F. The water enters the system, is heated, used (shower, laundry, etc) then goes down the drain. The water in a hydronic system is heated typically to 150°-200°F then circulates with a temperature drop of approximately 25°-35°. The heat dissipation (transfer) is very steady. Therefore, the recovery demand on a hydronic system is very significantly less than the demand on a general purpose water heater. Both instantaneous demand and overall demand are less on a hydronic system than on a general purpose water heater.

Aside, from recovery time, it is much easier to transfer electrically generated thermal energy than combustion generated thermal energy. Gas systems of all types have become much more efficient in recent years than in the past. In that respect manufacturers have narrowed the gap between electricity and combustible gases but electricity is still more efficient.

Thanks for the analysis George.

I think which is more cost effective would depend on the cost of gas and electricity in your area.

That’s right. Fluctuating energy costs make it difficult to pin down exactly which energy source would be the better choice. The best choice today may be the worst choice six months or a year from now. I was trying to stay more with the technical part in my answer; mainly to explain why recovery time is not usually a problem.

For what it is worth (and for anyone who might be interested), gases are the most complicated when doing financial analysis. The gas is often owned by produced or extracted fro the ground by one company, distributed on the network by another company, stored by another, and delivered to the consumer by still another. It is so complicated that gas brokerage (consulting) is a big business.

The quality of gas varies also. Some companies sell gas by the cubic foot and others by therms. Big consumers of gas prefer to buy by the therm because it is easier to calculate real energy costs than by the cubic foot. Terms that are often used in the gas industry “are at the gate” and “delivered to the gate”. A consumer may buy the gas by the therm but it can be commingled with gas having a energy value. It is then the gas utility’s responsibility to make sure you get the energy value that you paid for.

As the inspector, I have no concern which is the most economical. My concern is for the operability of the system on the coldest days of the winter. I am not a mechanical nor hydraulic engineer but I know that a 40 gal electric water heater is minimal for the hot water needs of a family of three. Add to that the ability to heat the entire living space of the home (1700 sqft) on the coldest days of the year and I have concerns.
I’ve been around 62 years and I have long since learned to listen to my concerns. Are they always well founded…NO. Are they correct enough to recommend an expert… Absolutely!

I think you made the right call Larry. Don’t get agitated. You asked what we thought.